package healthcheck

import (
	"bufio"
	"context"
	"crypto/x509"
	"errors"
	"fmt"
	"io"
	"sort"
	"strings"
	"time"

	"github.com/linkerd/linkerd2/controller/api/public"
	healthcheckPb "github.com/linkerd/linkerd2/controller/gen/common/healthcheck"
	configPb "github.com/linkerd/linkerd2/controller/gen/config"
	pb "github.com/linkerd/linkerd2/controller/gen/public"
	l5dcharts "github.com/linkerd/linkerd2/pkg/charts/linkerd2"
	"github.com/linkerd/linkerd2/pkg/config"
	"github.com/linkerd/linkerd2/pkg/identity"
	"github.com/linkerd/linkerd2/pkg/issuercerts"
	"github.com/linkerd/linkerd2/pkg/k8s"
	"github.com/linkerd/linkerd2/pkg/multicluster"
	"github.com/linkerd/linkerd2/pkg/tls"
	"github.com/linkerd/linkerd2/pkg/version"
	log "github.com/sirupsen/logrus"
	admissionRegistration "k8s.io/api/admissionregistration/v1beta1"
	appsv1 "k8s.io/api/apps/v1"
	corev1 "k8s.io/api/core/v1"
	kerrors "k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apimachinery/pkg/api/meta"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	yamlDecoder "k8s.io/apimachinery/pkg/util/yaml"
	k8sVersion "k8s.io/apimachinery/pkg/version"
	"k8s.io/client-go/kubernetes"
	apiregistrationv1client "k8s.io/kube-aggregator/pkg/client/clientset_generated/clientset/typed/apiregistration/v1"
	"sigs.k8s.io/yaml"
)

// CategoryID is an identifier for the types of health checks.
type CategoryID string

const (
	// KubernetesAPIChecks adds a series of checks to validate that the caller is
	// configured to interact with a working Kubernetes cluster.
	KubernetesAPIChecks CategoryID = "kubernetes-api"

	// KubernetesVersionChecks validate that the cluster meets the minimum version
	// requirements.
	KubernetesVersionChecks CategoryID = "kubernetes-version"

	// LinkerdPreInstall* checks enabled by `linkerd check --pre`

	// LinkerdPreInstallChecks adds checks to validate that the control plane
	// namespace does not already exist, and that the user can create cluster-wide
	// resources, including ClusterRole, ClusterRoleBinding, and
	// CustomResourceDefinition, as well as namespace-wide resources, including
	// Service, Deployment, and ConfigMap. This check only runs as part of the set
	// of pre-install checks.
	// This check is dependent on the output of KubernetesAPIChecks, so those
	// checks must be added first.
	LinkerdPreInstallChecks CategoryID = "pre-kubernetes-setup"

	// LinkerdPreInstallCapabilityChecks adds a check to validate the user has the
	// capabilities necessary to deploy Linkerd. For example, the NET_ADMIN and
	// NET_RAW capabilities are required by the `linkerd-init` container to modify
	// IP tables. These checks are not run when the `--linkerd-cni-enabled` flag
	// is set.
	LinkerdPreInstallCapabilityChecks CategoryID = "pre-kubernetes-capability"

	// LinkerdPreInstallGlobalResourcesChecks adds a series of checks to determine
	// the existence of the global resources like cluster roles, cluster role
	// bindings, mutating webhook configuration validating webhook configuration
	// and pod security policies during the pre-install phase. This check is used
	// to determine if a control plane is already installed.
	LinkerdPreInstallGlobalResourcesChecks CategoryID = "pre-linkerd-global-resources"

	// LinkerdConfigChecks enabled by `linkerd check config`

	// LinkerdConfigChecks adds a series of checks to validate that the Linkerd
	// namespace, RBAC, ServiceAccounts, and CRDs were successfully created.
	// These checks specifically validate that the `linkerd install config`
	// command succeeded in a multi-stage install, but also applies to a default
	// `linkerd install`.
	// These checks are dependent on the output of KubernetesAPIChecks, so those
	// checks must be added first.
	LinkerdConfigChecks CategoryID = "linkerd-config"

	// LinkerdIdentity Checks the integrity of the mTLS certificates
	// that the control plane is configured with
	LinkerdIdentity CategoryID = "linkerd-identity"

	// LinkerdWebhooksAndAPISvcTLS the integrity of the mTLS certificates
	// that of the for the injector and sp webhooks and the tap api svc
	LinkerdWebhooksAndAPISvcTLS CategoryID = "linkerd-webhooks-and-apisvc-tls"

	// LinkerdIdentityDataPlane checks that integrity of the mTLS
	// certificates that the proxies are configured with and tries to
	// report useful information with respect to whether the configuration
	// is compatible with the one of the control plane
	LinkerdIdentityDataPlane CategoryID = "linkerd-identity-data-plane"

	// LinkerdControlPlaneExistenceChecks adds a series of checks to validate that
	// the control plane namespace and controller pod exist.
	// These checks are dependent on the output of KubernetesAPIChecks, so those
	// checks must be added first.
	LinkerdControlPlaneExistenceChecks CategoryID = "linkerd-existence"

	// LinkerdAPIChecks adds a series of checks to validate that the control plane
	// is successfully serving the public API.
	// These checks are dependent on the output of KubernetesAPIChecks, so those
	// checks must be added first.
	LinkerdAPIChecks CategoryID = "linkerd-api"

	// LinkerdVersionChecks adds a series of checks to query for the latest
	// version, and validate the CLI is up to date.
	LinkerdVersionChecks CategoryID = "linkerd-version"

	// LinkerdControlPlaneVersionChecks adds a series of checks to validate that
	// the control plane is running the latest available version.
	// These checks are dependent on the following:
	// 1) `apiClient` from LinkerdControlPlaneExistenceChecks
	// 2) `latestVersions` from LinkerdVersionChecks
	// 3) `serverVersion` from `LinkerdControlPlaneExistenceChecks`
	LinkerdControlPlaneVersionChecks CategoryID = "control-plane-version"

	// LinkerdDataPlaneChecks adds data plane checks to validate that the data
	// plane namespace exists, and that the proxy containers are in a ready
	// state and running the latest available version.
	// These checks are dependent on the output of KubernetesAPIChecks,
	// `apiClient` from LinkerdControlPlaneExistenceChecks, and `latestVersions`
	// from LinkerdVersionChecks, so those checks must be added first.
	LinkerdDataPlaneChecks CategoryID = "linkerd-data-plane"

	// LinkerdHAChecks adds checks to validate that the HA configuration
	// is correct. These checks are no ops if linkerd is not in HA mode
	LinkerdHAChecks CategoryID = "linkerd-ha-checks"

	// LinkerdCNIPluginChecks adds checks to validate that the CNI
	/// plugin is installed and ready
	LinkerdCNIPluginChecks CategoryID = "linkerd-cni-plugin"

	// LinkerdCNIResourceLabel is the label key that is used to identify
	// whether a Kubernetes resource is related to the install-cni command
	// The value is expected to be "true", "false" or "", where "false" and
	// "" are equal, making "false" the default
	LinkerdCNIResourceLabel = "linkerd.io/cni-resource"

	linkerdCNIDisabledSkipReason = "skipping check because CNI is not enabled"
	linkerdCNIResourceName       = "linkerd-cni"
	linkerdCNIConfigMapName      = "linkerd-cni-config"

	// linkerdTapAPIServiceName is the name of the tap api service
	// This key is passed to checkApiService method to check whether
	// the api service is available or not
	linkerdTapAPIServiceName = "v1alpha1.tap.linkerd.io"

	tapOldTLSSecretName           = "linkerd-tap-tls"
	tapTLSSecretName              = "linkerd-tap-k8s-tls"
	proxyInjectorOldTLSSecretName = "linkerd-proxy-injector-tls"
	proxyInjectorTLSSecretName    = "linkerd-proxy-injector-k8s-tls"
	spValidatorOldTLSSecretName   = "linkerd-sp-validator-tls"
	spValidatorTLSSecretName      = "linkerd-sp-validator-k8s-tls"
	certOldKeyName                = "crt.pem"
	certKeyName                   = "tls.crt"
	keyOldKeyName                 = "key.pem"
	keyKeyName                    = "tls.key"
)

// HintBaseURL is the base URL on the linkerd.io website that all check hints
// point to. Each check adds its own `hintAnchor` to specify a location on the
// page.
const HintBaseURL = "https://linkerd.io/checks/#"

// AllowedClockSkew sets the allowed skew in clock synchronization
// between the system running inject command and the node(s), being
// based on assumed node's heartbeat interval (5 minutes) plus default TLS
// clock skew allowance.
//
// TODO: Make this default value overridable, e.g. by CLI flag
const AllowedClockSkew = 5*time.Minute + tls.DefaultClockSkewAllowance

var linkerdHAControlPlaneComponents = []string{
	"linkerd-controller",
	"linkerd-destination",
	"linkerd-identity",
	"linkerd-proxy-injector",
	"linkerd-sp-validator",
	"linkerd-tap",
}

// ExpectedServiceAccountNames is a list of the service accounts that a healthy
// Linkerd installation should have. Note that linkerd-heartbeat is optional,
// so it doesn't appear here.
var ExpectedServiceAccountNames = []string{
	"linkerd-controller",
	"linkerd-destination",
	"linkerd-identity",
	"linkerd-proxy-injector",
	"linkerd-sp-validator",
	"linkerd-web",
	"linkerd-tap",
}

var (
	retryWindow    = 5 * time.Second
	requestTimeout = 30 * time.Second
)

// Resource provides a way to describe a Kubernetes object, kind, and name.
// TODO: Consider sharing with the inject package's ResourceConfig.workload
// struct, as it wraps both runtime.Object and metav1.TypeMeta.
type Resource struct {
	groupVersionKind schema.GroupVersionKind
	name             string
}

// String outputs the resource in kind.group/name format, intended for
// `linkerd install`.
func (r *Resource) String() string {
	return fmt.Sprintf("%s/%s", strings.ToLower(r.groupVersionKind.GroupKind().String()), r.name)
}

// ResourceError provides a custom error type for resource existence checks,
// useful in printing detailed error messages in `linkerd check` and
// `linkerd install`.
type ResourceError struct {
	resourceName string
	Resources    []Resource
}

// Error satisfies the error interface for ResourceError. The output is intended
// for `linkerd check`.
func (e *ResourceError) Error() string {
	names := []string{}
	for _, res := range e.Resources {
		names = append(names, res.name)
	}
	return fmt.Sprintf("%s found but should not exist: %s", e.resourceName, strings.Join(names, " "))
}

// CategoryError provides a custom error type that also contains check category that emitted the error,
// useful when needed to distinguish between errors from multiple categories
type CategoryError struct {
	Category CategoryID
	Err      error
}

// Error satisfies the error interface for CategoryError.
func (e *CategoryError) Error() string {
	return e.Err.Error()
}

// IsCategoryError returns true if passed in error is of type CategoryError and belong to the given category
func IsCategoryError(err error, categoryID CategoryID) bool {
	if ce, ok := err.(*CategoryError); ok {
		return ce.Category == categoryID
	}
	return false
}

// SkipError is returned by a check in case this check needs to be ignored.
type SkipError struct {
	Reason string
}

// Error satisfies the error interface for SkipError.
func (e *SkipError) Error() string {
	return e.Reason
}

// VerboseSuccess implements the error interface but represents a success with
// a message.
type VerboseSuccess struct {
	Message string
}

// Error satisfies the error interface for VerboseSuccess.  Since VerboseSuccess
// does not actually represent a failure, this returns the empty string.
func (e *VerboseSuccess) Error() string {
	return ""
}

type checker struct {
	// description is the short description that's printed to the command line
	// when the check is executed
	description string

	// hintAnchor, when appended to `HintBaseURL`, provides a URL to more
	// information about the check
	hintAnchor string

	// fatal indicates that all remaining checks should be aborted if this check
	// fails; it should only be used if subsequent checks cannot possibly succeed
	// (default false)
	fatal bool

	// warning indicates that if this check fails, it should be reported, but it
	// should not impact the overall outcome of the health check (default false)
	warning bool

	// retryDeadline establishes a deadline before which this check should be
	// retried; if the deadline has passed, the check fails (default: no retries)
	retryDeadline time.Time

	// surfaceErrorOnRetry indicates that the error message should be displayed
	// even if the check will be retried.  This is useful if the error message
	// contains the current status of the check.
	surfaceErrorOnRetry bool

	// check is the function that's called to execute the check; if the function
	// returns an error, the check fails
	check func(context.Context) error

	// checkRPC is an alternative to check that can be used to perform a remote
	// check using the SelfCheck gRPC endpoint; check status is based on the value
	// of the gRPC response
	checkRPC func(context.Context) (*healthcheckPb.SelfCheckResponse, error)
}

// CheckResult encapsulates a check's identifying information and output
// Note there exists an analogous user-facing type, `cmd.check`, for output via
// `linkerd check -o json`.
type CheckResult struct {
	Category    CategoryID
	Description string
	HintAnchor  string
	Retry       bool
	Warning     bool
	Err         error
}

// CheckObserver receives the results of each check.
type CheckObserver func(*CheckResult)

type category struct {
	id       CategoryID
	checkers []checker
	enabled  bool
}

// Options specifies configuration for a HealthChecker.
type Options struct {
	ControlPlaneNamespace string
	CNINamespace          string
	DataPlaneNamespace    string
	KubeConfig            string
	KubeContext           string
	Impersonate           string
	ImpersonateGroup      []string
	APIAddr               string
	VersionOverride       string
	RetryDeadline         time.Time
	CNIEnabled            bool
	InstallManifest       string
	MultiCluster          bool
}

// HealthChecker encapsulates all health check checkers, and clients required to
// perform those checks.
type HealthChecker struct {
	categories []category
	*Options

	// these fields are set in the process of running checks
	kubeAPI          *k8s.KubernetesAPI
	kubeVersion      *k8sVersion.Info
	controlPlanePods []corev1.Pod
	apiClient        public.APIClient
	latestVersions   version.Channels
	serverVersion    string
	linkerdConfig    *l5dcharts.Values
	uuid             string
	issuerCert       *tls.Cred
	trustAnchors     []*x509.Certificate
	cniDaemonSet     *appsv1.DaemonSet
	links            []multicluster.Link
}

// NewHealthChecker returns an initialized HealthChecker
func NewHealthChecker(categoryIDs []CategoryID, options *Options) *HealthChecker {
	hc := &HealthChecker{
		Options: options,
	}

	hc.categories = append(hc.allCategories(), hc.addOnCategories()...)
	hc.categories = append(hc.categories, hc.multiClusterCategory()...)

	checkMap := map[CategoryID]struct{}{}
	for _, category := range categoryIDs {
		checkMap[category] = struct{}{}
	}
	for i := range hc.categories {
		if _, ok := checkMap[hc.categories[i].id]; ok {
			hc.categories[i].enabled = true
		}
	}

	return hc
}

// allCategories is the global, ordered list of all checkers, grouped by
// category. This method is attached to the HealthChecker struct because the
// checkers directly reference other members of the struct, such as kubeAPI,
// controlPlanePods, etc.
//
// Ordering is important because checks rely on specific `HealthChecker` members
// getting populated by earlier checks, such as kubeAPI, controlPlanePods, etc.
//
// Note that all checks should include a `hintAnchor` with a corresponding section
// in the linkerd check faq:
// https://linkerd.io/checks/#
func (hc *HealthChecker) allCategories() []category {
	return []category{
		{
			id: KubernetesAPIChecks,
			checkers: []checker{
				{
					description: "can initialize the client",
					hintAnchor:  "k8s-api",
					fatal:       true,
					check: func(context.Context) (err error) {
						hc.kubeAPI, err = k8s.NewAPI(hc.KubeConfig, hc.KubeContext, hc.Impersonate, hc.ImpersonateGroup, requestTimeout)
						return
					},
				},
				{
					description: "can query the Kubernetes API",
					hintAnchor:  "k8s-api",
					fatal:       true,
					check: func(ctx context.Context) (err error) {
						hc.kubeVersion, err = hc.kubeAPI.GetVersionInfo()
						return
					},
				},
			},
		},
		{
			id: KubernetesVersionChecks,
			checkers: []checker{
				{
					description: "is running the minimum Kubernetes API version",
					hintAnchor:  "k8s-version",
					check: func(context.Context) error {
						return hc.kubeAPI.CheckVersion(hc.kubeVersion)
					},
				},
				{
					description: "is running the minimum kubectl version",
					hintAnchor:  "kubectl-version",
					check: func(context.Context) error {
						return k8s.CheckKubectlVersion()
					},
				},
			},
		},
		{
			id: LinkerdPreInstallChecks,
			checkers: []checker{
				{
					description: "control plane namespace does not already exist",
					hintAnchor:  "pre-ns",
					check: func(ctx context.Context) error {
						return hc.checkNamespace(ctx, hc.ControlPlaneNamespace, false)
					},
				},
				{
					description: "can create non-namespaced resources",
					hintAnchor:  "pre-k8s-cluster-k8s",
					check: func(ctx context.Context) error {
						return hc.checkCanCreateNonNamespacedResources(ctx)
					},
				},
				{
					description: "can create ServiceAccounts",
					hintAnchor:  "pre-k8s",
					check: func(ctx context.Context) error {
						return hc.checkCanCreate(ctx, hc.ControlPlaneNamespace, "", "v1", "serviceaccounts")
					},
				},
				{
					description: "can create Services",
					hintAnchor:  "pre-k8s",
					check: func(ctx context.Context) error {
						return hc.checkCanCreate(ctx, hc.ControlPlaneNamespace, "", "v1", "services")
					},
				},
				{
					description: "can create Deployments",
					hintAnchor:  "pre-k8s",
					check: func(ctx context.Context) error {
						return hc.checkCanCreate(ctx, hc.ControlPlaneNamespace, "apps", "v1", "deployments")
					},
				},
				{
					description: "can create CronJobs",
					hintAnchor:  "pre-k8s",
					check: func(ctx context.Context) error {
						return hc.checkCanCreate(ctx, hc.ControlPlaneNamespace, "batch", "v1beta1", "cronjobs")
					},
				},
				{
					description: "can create ConfigMaps",
					hintAnchor:  "pre-k8s",
					check: func(ctx context.Context) error {
						return hc.checkCanCreate(ctx, hc.ControlPlaneNamespace, "", "v1", "configmaps")
					},
				},
				{
					description: "can create Secrets",
					hintAnchor:  "pre-k8s",
					check: func(ctx context.Context) error {
						return hc.checkCanCreate(ctx, hc.ControlPlaneNamespace, "", "v1", "secrets")
					},
				},
				{
					description: "can read Secrets",
					hintAnchor:  "pre-k8s",
					check: func(ctx context.Context) error {
						return hc.checkCanGet(ctx, hc.ControlPlaneNamespace, "", "v1", "secrets")
					},
				},
				{
					description: "can read extension-apiserver-authentication configmap",
					hintAnchor:  "pre-k8s",
					check: func(ctx context.Context) error {
						return hc.checkExtensionAPIServerAuthentication(ctx)
					},
				},
				{
					description: "no clock skew detected",
					hintAnchor:  "pre-k8s-clock-skew",
					warning:     true,
					check: func(ctx context.Context) error {
						return hc.checkClockSkew(ctx)
					},
				},
			},
		},
		{
			id: LinkerdPreInstallCapabilityChecks,
			checkers: []checker{
				{
					description: "has NET_ADMIN capability",
					hintAnchor:  "pre-k8s-cluster-net-admin",
					warning:     true,
					check: func(ctx context.Context) error {
						return hc.checkCapability(ctx, "NET_ADMIN")
					},
				},
				{
					description: "has NET_RAW capability",
					hintAnchor:  "pre-k8s-cluster-net-raw",
					warning:     true,
					check: func(ctx context.Context) error {
						return hc.checkCapability(ctx, "NET_RAW")
					},
				},
			},
		},
		{
			id: LinkerdPreInstallGlobalResourcesChecks,
			checkers: []checker{
				{
					description: "no ClusterRoles exist",
					hintAnchor:  "pre-l5d-existence",
					check: func(ctx context.Context) error {
						return hc.checkClusterRoles(ctx, false, hc.expectedRBACNames(), hc.controlPlaneComponentsSelector())
					},
				},
				{
					description: "no ClusterRoleBindings exist",
					hintAnchor:  "pre-l5d-existence",
					check: func(ctx context.Context) error {
						return hc.checkClusterRoleBindings(ctx, false, hc.expectedRBACNames(), hc.controlPlaneComponentsSelector())
					},
				},
				{
					description: "no CustomResourceDefinitions exist",
					hintAnchor:  "pre-l5d-existence",
					check: func(ctx context.Context) error {
						return hc.checkCustomResourceDefinitions(ctx, false)
					},
				},
				{
					description: "no MutatingWebhookConfigurations exist",
					hintAnchor:  "pre-l5d-existence",
					check: func(ctx context.Context) error {
						return hc.checkMutatingWebhookConfigurations(ctx, false)
					},
				},
				{
					description: "no ValidatingWebhookConfigurations exist",
					hintAnchor:  "pre-l5d-existence",
					check: func(ctx context.Context) error {
						return hc.checkValidatingWebhookConfigurations(ctx, false)
					},
				},
				{
					description: "no PodSecurityPolicies exist",
					hintAnchor:  "pre-l5d-existence",
					check: func(ctx context.Context) error {
						return hc.checkPodSecurityPolicies(ctx, false)
					},
				},
			},
		},
		{
			id: LinkerdControlPlaneExistenceChecks,
			checkers: []checker{
				{
					description: "'linkerd-config' config map exists",
					hintAnchor:  "l5d-existence-linkerd-config",
					fatal:       true,
					check: func(ctx context.Context) (err error) {
						hc.uuid, hc.linkerdConfig, err = hc.checkLinkerdConfigConfigMap(ctx)

						if hc.linkerdConfig != nil {
							hc.CNIEnabled = hc.linkerdConfig.Global.CNIEnabled
						}
						return
					},
				},
				{
					description: "heartbeat ServiceAccount exist",
					hintAnchor:  "l5d-existence-sa",
					fatal:       true,
					check: func(ctx context.Context) error {
						if hc.isHeartbeatDisabled() {
							return nil
						}
						return hc.checkServiceAccounts(ctx, []string{"linkerd-heartbeat"}, hc.ControlPlaneNamespace, hc.controlPlaneComponentsSelector())
					},
				},
				{
					description:   "control plane replica sets are ready",
					hintAnchor:    "l5d-existence-replicasets",
					retryDeadline: hc.RetryDeadline,
					fatal:         true,
					check: func(ctx context.Context) error {
						controlPlaneReplicaSet, err := hc.kubeAPI.GetReplicaSets(ctx, hc.ControlPlaneNamespace)
						if err != nil {
							return err
						}
						return checkControlPlaneReplicaSets(controlPlaneReplicaSet)
					},
				},
				{
					description:         "no unschedulable pods",
					hintAnchor:          "l5d-existence-unschedulable-pods",
					retryDeadline:       hc.RetryDeadline,
					surfaceErrorOnRetry: true,
					warning:             true,
					check: func(ctx context.Context) error {
						// do not save this into hc.controlPlanePods, as this check may
						// succeed prior to all expected control plane pods being up
						controlPlanePods, err := hc.kubeAPI.GetPodsByNamespace(ctx, hc.ControlPlaneNamespace)
						if err != nil {
							return err
						}
						return checkUnschedulablePods(controlPlanePods)
					},
				},
				{
					description:         "controller pod is running",
					hintAnchor:          "l5d-existence-controller",
					retryDeadline:       hc.RetryDeadline,
					surfaceErrorOnRetry: true,
					fatal:               true,
					check: func(ctx context.Context) error {
						// save this into hc.controlPlanePods, since this check only
						// succeeds when all pods are up
						var err error
						hc.controlPlanePods, err = hc.kubeAPI.GetPodsByNamespace(ctx, hc.ControlPlaneNamespace)
						if err != nil {
							return err
						}

						return checkContainerRunning(hc.controlPlanePods, "controller")
					},
				},
				{
					description: "can initialize the client",
					hintAnchor:  "l5d-existence-client",
					fatal:       true,
					check: func(ctx context.Context) (err error) {
						if hc.APIAddr != "" {
							hc.apiClient, err = public.NewInternalClient(hc.ControlPlaneNamespace, hc.APIAddr)
						} else {
							hc.apiClient, err = public.NewExternalClient(ctx, hc.ControlPlaneNamespace, hc.kubeAPI)
						}
						return
					},
				},
				{
					description:   "can query the control plane API",
					hintAnchor:    "l5d-existence-api",
					retryDeadline: hc.RetryDeadline,
					fatal:         true,
					check: func(ctx context.Context) (err error) {
						hc.serverVersion, err = GetServerVersion(ctx, hc.apiClient)
						return
					},
				},
			},
		},
		{
			id: LinkerdConfigChecks,
			checkers: []checker{
				{
					description: "control plane Namespace exists",
					hintAnchor:  "l5d-existence-ns",
					fatal:       true,
					check: func(ctx context.Context) error {
						return hc.checkNamespace(ctx, hc.ControlPlaneNamespace, true)
					},
				},
				{
					description: "control plane ClusterRoles exist",
					hintAnchor:  "l5d-existence-cr",
					fatal:       true,
					check: func(ctx context.Context) error {
						return hc.checkClusterRoles(ctx, true, hc.expectedRBACNames(), hc.controlPlaneComponentsSelector())
					},
				},
				{
					description: "control plane ClusterRoleBindings exist",
					hintAnchor:  "l5d-existence-crb",
					fatal:       true,
					check: func(ctx context.Context) error {
						return hc.checkClusterRoleBindings(ctx, true, hc.expectedRBACNames(), hc.controlPlaneComponentsSelector())
					},
				},
				{
					description: "control plane ServiceAccounts exist",
					hintAnchor:  "l5d-existence-sa",
					fatal:       true,
					check: func(ctx context.Context) error {
						return hc.checkServiceAccounts(ctx, ExpectedServiceAccountNames, hc.ControlPlaneNamespace, hc.controlPlaneComponentsSelector())
					},
				},
				{
					description: "control plane CustomResourceDefinitions exist",
					hintAnchor:  "l5d-existence-crd",
					fatal:       true,
					check: func(ctx context.Context) error {
						return hc.checkCustomResourceDefinitions(ctx, true)
					},
				},
				{
					description: "control plane MutatingWebhookConfigurations exist",
					hintAnchor:  "l5d-existence-mwc",
					fatal:       true,
					check: func(ctx context.Context) error {
						return hc.checkMutatingWebhookConfigurations(ctx, true)
					},
				},
				{
					description: "control plane ValidatingWebhookConfigurations exist",
					hintAnchor:  "l5d-existence-vwc",
					fatal:       true,
					check: func(ctx context.Context) error {
						return hc.checkValidatingWebhookConfigurations(ctx, true)
					},
				},
				{
					description: "control plane PodSecurityPolicies exist",
					hintAnchor:  "l5d-existence-psp",
					fatal:       true,
					check: func(ctx context.Context) error {
						return hc.checkPodSecurityPolicies(ctx, true)
					},
				},
			},
		},
		{
			id: LinkerdCNIPluginChecks,
			checkers: []checker{
				{
					description: "cni plugin ConfigMap exists",
					hintAnchor:  "cni-plugin-cm-exists",
					fatal:       true,
					check: func(ctx context.Context) error {
						if !hc.CNIEnabled {
							return &SkipError{Reason: linkerdCNIDisabledSkipReason}
						}
						_, err := hc.kubeAPI.CoreV1().ConfigMaps(hc.CNINamespace).Get(ctx, linkerdCNIConfigMapName, metav1.GetOptions{})
						return err
					},
				},
				{
					description: "cni plugin PodSecurityPolicy exists",
					hintAnchor:  "cni-plugin-psp-exists",
					fatal:       true,
					check: func(ctx context.Context) error {
						if !hc.CNIEnabled {
							return &SkipError{Reason: linkerdCNIDisabledSkipReason}
						}
						pspName := fmt.Sprintf("linkerd-%s-cni", hc.CNINamespace)
						_, err := hc.kubeAPI.PolicyV1beta1().PodSecurityPolicies().Get(ctx, pspName, metav1.GetOptions{})
						if kerrors.IsNotFound(err) {
							return fmt.Errorf("missing PodSecurityPolicy: %s", pspName)
						}
						return err
					},
				},
				{
					description: "cni plugin ClusterRole exists",
					hintAnchor:  "cni-plugin-cr-exists",
					fatal:       true,
					check: func(ctx context.Context) error {
						if !hc.CNIEnabled {
							return &SkipError{Reason: linkerdCNIDisabledSkipReason}
						}
						_, err := hc.kubeAPI.RbacV1().ClusterRoles().Get(ctx, linkerdCNIResourceName, metav1.GetOptions{})
						if kerrors.IsNotFound(err) {
							return fmt.Errorf("missing ClusterRole: %s", linkerdCNIResourceName)
						}
						return err
					},
				},
				{
					description: "cni plugin ClusterRoleBinding exists",
					hintAnchor:  "cni-plugin-crb-exists",
					fatal:       true,
					check: func(ctx context.Context) error {
						if !hc.CNIEnabled {
							return &SkipError{Reason: linkerdCNIDisabledSkipReason}
						}
						_, err := hc.kubeAPI.RbacV1().ClusterRoleBindings().Get(ctx, linkerdCNIResourceName, metav1.GetOptions{})
						if kerrors.IsNotFound(err) {
							return fmt.Errorf("missing ClusterRoleBinding: %s", linkerdCNIResourceName)
						}
						return err
					},
				},
				{
					description: "cni plugin Role exists",
					hintAnchor:  "cni-plugin-r-exists",
					fatal:       true,
					check: func(ctx context.Context) error {
						if !hc.CNIEnabled {
							return &SkipError{Reason: linkerdCNIDisabledSkipReason}
						}
						_, err := hc.kubeAPI.RbacV1().Roles(hc.CNINamespace).Get(ctx, linkerdCNIResourceName, metav1.GetOptions{})
						if kerrors.IsNotFound(err) {
							return fmt.Errorf("missing Role: %s", linkerdCNIResourceName)
						}
						return err
					},
				},
				{
					description: "cni plugin RoleBinding exists",
					hintAnchor:  "cni-plugin-rb-exists",
					fatal:       true,
					check: func(ctx context.Context) error {
						if !hc.CNIEnabled {
							return &SkipError{Reason: linkerdCNIDisabledSkipReason}
						}
						_, err := hc.kubeAPI.RbacV1().RoleBindings(hc.CNINamespace).Get(ctx, linkerdCNIResourceName, metav1.GetOptions{})
						if kerrors.IsNotFound(err) {
							return fmt.Errorf("missing RoleBinding: %s", linkerdCNIResourceName)
						}
						return err
					},
				},
				{
					description: "cni plugin ServiceAccount exists",
					hintAnchor:  "cni-plugin-sa-exists",
					fatal:       true,
					check: func(ctx context.Context) error {
						if !hc.CNIEnabled {
							return &SkipError{Reason: linkerdCNIDisabledSkipReason}
						}
						_, err := hc.kubeAPI.CoreV1().ServiceAccounts(hc.CNINamespace).Get(ctx, linkerdCNIResourceName, metav1.GetOptions{})
						if kerrors.IsNotFound(err) {
							return fmt.Errorf("missing ServiceAccount: %s", linkerdCNIResourceName)
						}
						return err
					},
				},
				{
					description: "cni plugin DaemonSet exists",
					hintAnchor:  "cni-plugin-ds-exists",
					fatal:       true,
					check: func(ctx context.Context) (err error) {
						if !hc.CNIEnabled {
							return &SkipError{Reason: linkerdCNIDisabledSkipReason}
						}
						hc.cniDaemonSet, err = hc.kubeAPI.Interface.AppsV1().DaemonSets(hc.CNINamespace).Get(ctx, linkerdCNIResourceName, metav1.GetOptions{})
						if kerrors.IsNotFound(err) {
							return fmt.Errorf("missing DaemonSet: %s", linkerdCNIResourceName)
						}
						return err
					},
				},
				{
					description:         "cni plugin pod is running on all nodes",
					hintAnchor:          "cni-plugin-ready",
					retryDeadline:       hc.RetryDeadline,
					surfaceErrorOnRetry: true,
					fatal:               true,
					check: func(ctx context.Context) (err error) {
						if !hc.CNIEnabled {
							return &SkipError{Reason: linkerdCNIDisabledSkipReason}
						}
						hc.cniDaemonSet, err = hc.kubeAPI.Interface.AppsV1().DaemonSets(hc.CNINamespace).Get(ctx, linkerdCNIResourceName, metav1.GetOptions{})
						if kerrors.IsNotFound(err) {
							return fmt.Errorf("missing DaemonSet: %s", linkerdCNIResourceName)
						}
						scheduled := hc.cniDaemonSet.Status.DesiredNumberScheduled
						ready := hc.cniDaemonSet.Status.NumberReady
						if scheduled != ready {
							return fmt.Errorf("number ready: %d, number scheduled: %d", ready, scheduled)
						}
						return nil
					},
				},
			},
		},
		{
			id: LinkerdIdentity,
			checkers: []checker{
				{
					description: "certificate config is valid",
					hintAnchor:  "l5d-identity-cert-config-valid",
					fatal:       true,
					check: func(ctx context.Context) (err error) {
						hc.issuerCert, hc.trustAnchors, err = hc.checkCertificatesConfig(ctx)
						return
					},
				},
				{
					description: "trust anchors are using supported crypto algorithm",
					hintAnchor:  "l5d-identity-trustAnchors-use-supported-crypto",
					fatal:       true,
					check: func(context.Context) error {
						var invalidAnchors []string
						for _, anchor := range hc.trustAnchors {
							if err := issuercerts.CheckCertAlgoRequirements(anchor); err != nil {
								invalidAnchors = append(invalidAnchors, fmt.Sprintf("* %v %s %s", anchor.SerialNumber, anchor.Subject.CommonName, err))
							}
						}
						if len(invalidAnchors) > 0 {
							return fmt.Errorf("Invalid trustAnchors:\n\t%s", strings.Join(invalidAnchors, "\n\t"))
						}
						return nil
					},
				},
				{
					description: "trust anchors are within their validity period",
					hintAnchor:  "l5d-identity-trustAnchors-are-time-valid",
					fatal:       true,
					check: func(ctx context.Context) error {
						var expiredAnchors []string
						for _, anchor := range hc.trustAnchors {
							if err := issuercerts.CheckCertValidityPeriod(anchor); err != nil {
								expiredAnchors = append(expiredAnchors, fmt.Sprintf("* %v %s %s", anchor.SerialNumber, anchor.Subject.CommonName, err))
							}
						}
						if len(expiredAnchors) > 0 {
							return fmt.Errorf("Invalid anchors:\n\t%s", strings.Join(expiredAnchors, "\n\t"))
						}

						return nil
					},
				},
				{
					description: "trust anchors are valid for at least 60 days",
					hintAnchor:  "l5d-identity-trustAnchors-not-expiring-soon",
					warning:     true,
					check: func(ctx context.Context) error {
						var expiringAnchors []string
						for _, anchor := range hc.trustAnchors {
							if err := issuercerts.CheckExpiringSoon(anchor); err != nil {
								expiringAnchors = append(expiringAnchors, fmt.Sprintf("* %v %s %s", anchor.SerialNumber, anchor.Subject.CommonName, err))
							}
						}
						if len(expiringAnchors) > 0 {
							return fmt.Errorf("Anchors expiring soon:\n\t%s", strings.Join(expiringAnchors, "\n\t"))
						}
						return nil
					},
				},
				{
					description: "issuer cert is using supported crypto algorithm",
					hintAnchor:  "l5d-identity-issuer-cert-uses-supported-crypto",
					fatal:       true,
					check: func(context.Context) error {
						if err := issuercerts.CheckCertAlgoRequirements(hc.issuerCert.Certificate); err != nil {
							return fmt.Errorf("issuer certificate %s", err)
						}
						return nil
					},
				},
				{
					description: "issuer cert is within its validity period",
					hintAnchor:  "l5d-identity-issuer-cert-is-time-valid",
					fatal:       true,
					check: func(ctx context.Context) error {
						if err := issuercerts.CheckCertValidityPeriod(hc.issuerCert.Certificate); err != nil {
							return fmt.Errorf("issuer certificate is %s", err)
						}
						return nil
					},
				},
				{
					description: "issuer cert is valid for at least 60 days",
					warning:     true,
					hintAnchor:  "l5d-identity-issuer-cert-not-expiring-soon",
					check: func(context.Context) error {
						if err := issuercerts.CheckExpiringSoon(hc.issuerCert.Certificate); err != nil {
							return fmt.Errorf("issuer certificate %s", err)
						}
						return nil
					},
				},
				{
					description: "issuer cert is issued by the trust anchor",
					hintAnchor:  "l5d-identity-issuer-cert-issued-by-trust-anchor",
					check: func(ctx context.Context) error {
						return hc.issuerCert.Verify(tls.CertificatesToPool(hc.trustAnchors), hc.issuerIdentity(), time.Time{})
					},
				},
			},
		},
		{
			id: LinkerdWebhooksAndAPISvcTLS,
			checkers: []checker{
				{
					description: "tap API server has valid cert",
					hintAnchor:  "l5d-tap-cert-valid",
					fatal:       true,
					check: func(ctx context.Context) (err error) {
						anchors, err := hc.fetchTapCaBundle(ctx)
						if err != nil {
							return err
						}
						cert, err := hc.fetchCredsFromSecret(ctx, tapTLSSecretName)
						if kerrors.IsNotFound(err) {
							cert, err = hc.fetchCredsFromOldSecret(ctx, tapOldTLSSecretName)
						}
						if err != nil {
							return err
						}

						identityName := fmt.Sprintf("linkerd-tap.%s.svc", hc.ControlPlaneNamespace)
						return hc.checkCertAndAnchors(cert, anchors, identityName)
					},
				},
				{
					description: "proxy-injector webhook has valid cert",
					hintAnchor:  "l5d-proxy-injector-webhook-cert-valid",
					fatal:       true,
					check: func(ctx context.Context) (err error) {
						anchors, err := hc.fetchProxyInjectorCaBundle(ctx)
						if err != nil {
							return err
						}
						cert, err := hc.fetchCredsFromSecret(ctx, proxyInjectorTLSSecretName)
						if kerrors.IsNotFound(err) {
							cert, err = hc.fetchCredsFromOldSecret(ctx, proxyInjectorOldTLSSecretName)
						}
						if err != nil {
							return err
						}

						identityName := fmt.Sprintf("linkerd-proxy-injector.%s.svc", hc.ControlPlaneNamespace)
						return hc.checkCertAndAnchors(cert, anchors, identityName)
					},
				},
				{
					description: "sp-validator webhook has valid cert",
					hintAnchor:  "l5d-sp-validator-webhook-cert-valid",
					fatal:       true,
					check: func(ctx context.Context) (err error) {
						anchors, err := hc.fetchSpValidatorCaBundle(ctx)
						if err != nil {
							return err
						}
						cert, err := hc.fetchCredsFromSecret(ctx, spValidatorTLSSecretName)
						if kerrors.IsNotFound(err) {
							cert, err = hc.fetchCredsFromOldSecret(ctx, spValidatorOldTLSSecretName)
						}
						if err != nil {
							return err
						}
						identityName := fmt.Sprintf("linkerd-sp-validator.%s.svc", hc.ControlPlaneNamespace)
						return hc.checkCertAndAnchors(cert, anchors, identityName)
					},
				},
			},
		},
		{
			id: LinkerdIdentityDataPlane,
			checkers: []checker{
				{
					description: "data plane proxies certificate match CA",
					hintAnchor:  "l5d-identity-data-plane-proxies-certs-match-ca",
					warning:     true,
					check: func(ctx context.Context) error {
						return hc.checkDataPlaneProxiesCertificate(ctx)
					},
				},
			},
		},
		{
			id: LinkerdAPIChecks,
			checkers: []checker{
				{
					description:         "control plane pods are ready",
					hintAnchor:          "l5d-api-control-ready",
					retryDeadline:       hc.RetryDeadline,
					surfaceErrorOnRetry: true,
					fatal:               true,
					check: func(ctx context.Context) error {
						var err error
						hc.controlPlanePods, err = hc.kubeAPI.GetPodsByNamespace(ctx, hc.ControlPlaneNamespace)
						if err != nil {
							return err
						}
						return validateControlPlanePods(hc.controlPlanePods)
					},
				},
				{
					description: "control plane self-check",
					hintAnchor:  "l5d-api-control-api",
					// to avoid confusing users with a prometheus readiness error, we only show
					// "waiting for check to complete" while things converge. If after the timeout
					// it still hasn't converged, we show the real error (a 503 usually).
					surfaceErrorOnRetry: false,
					fatal:               true,
					retryDeadline:       hc.RetryDeadline,
					checkRPC: func(ctx context.Context) (*healthcheckPb.SelfCheckResponse, error) {
						return hc.apiClient.SelfCheck(ctx, &healthcheckPb.SelfCheckRequest{})
					},
				},
				{
					description: "tap api service is running",
					hintAnchor:  "l5d-tap-api",
					warning:     true,
					check: func(ctx context.Context) error {
						return hc.checkAPIService(ctx, linkerdTapAPIServiceName)
					},
				},
			},
		},
		{
			id: LinkerdVersionChecks,
			checkers: []checker{
				{
					description: "can determine the latest version",
					hintAnchor:  "l5d-version-latest",
					warning:     true,
					check: func(ctx context.Context) (err error) {
						if hc.VersionOverride != "" {
							hc.latestVersions, err = version.NewChannels(hc.VersionOverride)
						} else {
							uuid := "unknown"
							if hc.uuid != "" {
								uuid = hc.uuid
							}
							hc.latestVersions, err = version.GetLatestVersions(ctx, uuid, "cli")
						}
						return
					},
				},
				{
					description: "cli is up-to-date",
					hintAnchor:  "l5d-version-cli",
					warning:     true,
					check: func(context.Context) error {
						return hc.latestVersions.Match(version.Version)
					},
				},
			},
		},
		{
			id: LinkerdControlPlaneVersionChecks,
			checkers: []checker{
				{
					description: "control plane is up-to-date",
					hintAnchor:  "l5d-version-control",
					warning:     true,
					check: func(context.Context) error {
						return hc.latestVersions.Match(hc.serverVersion)
					},
				},
				{
					description: "control plane and cli versions match",
					hintAnchor:  "l5d-version-control",
					warning:     true,
					check: func(context.Context) error {
						if hc.serverVersion != version.Version {
							return fmt.Errorf("control plane running %s but cli running %s", hc.serverVersion, version.Version)
						}
						return nil
					},
				},
			},
		},
		{
			id: LinkerdDataPlaneChecks,
			checkers: []checker{
				{
					description: "data plane namespace exists",
					hintAnchor:  "l5d-data-plane-exists",
					fatal:       true,
					check: func(ctx context.Context) error {
						if hc.DataPlaneNamespace == "" {
							// when checking proxies in all namespaces, this check is a no-op
							return nil
						}
						return hc.checkNamespace(ctx, hc.DataPlaneNamespace, true)
					},
				},
				{
					description:   "data plane proxies are ready",
					hintAnchor:    "l5d-data-plane-ready",
					retryDeadline: hc.RetryDeadline,
					fatal:         true,
					check: func(ctx context.Context) error {
						pods, err := hc.getDataPlanePods(ctx)
						if err != nil {
							return err
						}

						return validateDataPlanePods(pods, hc.DataPlaneNamespace)
					},
				},
				{
					description:   "data plane proxy metrics are present in Prometheus",
					hintAnchor:    "l5d-data-plane-prom",
					retryDeadline: hc.RetryDeadline,
					check: func(ctx context.Context) error {
						pods, err := hc.getDataPlanePods(ctx)
						if err != nil {
							return err
						}

						// Check if prometheus configured
						prometheusValues := make(map[string]interface{})
						err = yaml.Unmarshal(hc.linkerdConfig.Prometheus.Values(), &prometheusValues)
						if err != nil {
							return err
						}
						if !GetBool(prometheusValues, "enabled") && hc.linkerdConfig.Global.PrometheusURL == "" {
							return &SkipError{Reason: "no prometheus instance to connect"}
						}

						return validateDataPlanePodReporting(pods)
					},
				},
				{
					description: "data plane is up-to-date",
					hintAnchor:  "l5d-data-plane-version",
					warning:     true,
					check: func(ctx context.Context) error {
						pods, err := hc.getDataPlanePods(ctx)
						if err != nil {
							return err
						}

						outdatedPods := []string{}
						for _, pod := range pods {
							err = hc.latestVersions.Match(pod.ProxyVersion)
							if err != nil {
								outdatedPods = append(outdatedPods, fmt.Sprintf("\t* %s (%s)", pod.Name, pod.ProxyVersion))
							}
						}
						if len(outdatedPods) > 0 {
							podList := strings.Join(outdatedPods, "\n")
							return fmt.Errorf("Some data plane pods are not running the current version:\n%s", podList)
						}
						return nil
					},
				},
				{
					description: "data plane and cli versions match",
					hintAnchor:  "l5d-data-plane-cli-version",
					warning:     true,
					check: func(ctx context.Context) error {
						pods, err := hc.getDataPlanePods(ctx)
						if err != nil {
							return err
						}

						for _, pod := range pods {
							if pod.ProxyVersion != version.Version {
								return fmt.Errorf("%s running %s but cli running %s", pod.Name, pod.ProxyVersion, version.Version)
							}
						}
						return nil
					},
				},
			},
		},
		{
			id: LinkerdHAChecks,
			checkers: []checker{
				{
					description: "pod injection disabled on kube-system",
					hintAnchor:  "l5d-injection-disabled",
					warning:     true,
					check: func(ctx context.Context) error {
						policy, err := hc.getMutatingWebhookFailurePolicy(ctx)
						if err != nil {
							return err
						}
						if policy != nil && *policy == admissionRegistration.Fail {
							return hc.checkHAMetadataPresentOnKubeSystemNamespace(ctx)
						}
						return &SkipError{Reason: "not run for non HA installs"}
					},
				},
				{
					description:   "multiple replicas of control plane pods",
					hintAnchor:    "l5d-control-plane-replicas",
					retryDeadline: hc.RetryDeadline,
					warning:       true,
					check: func(ctx context.Context) error {
						if hc.isHA() {
							return hc.checkMinReplicasAvailable(ctx)
						}
						return &SkipError{Reason: "not run for non HA installs"}
					},
				},
			},
		},
	}
}

func (hc *HealthChecker) checkCertAndAnchors(cert *tls.Cred, trustAnchors []*x509.Certificate, identityName string) error {

	// check anchors time validity
	var expiredAnchors []string
	for _, anchor := range trustAnchors {
		if err := issuercerts.CheckCertValidityPeriod(anchor); err != nil {
			expiredAnchors = append(expiredAnchors, fmt.Sprintf("* %v %s %s", anchor.SerialNumber, anchor.Subject.CommonName, err))
		}
	}
	if len(expiredAnchors) > 0 {
		return fmt.Errorf("Anchors not within their validity period:\n\t%s", strings.Join(expiredAnchors, "\n\t"))
	}

	// check anchors not expiring soon
	var expiringAnchors []string
	for _, anchor := range trustAnchors {
		anchor := anchor
		if err := issuercerts.CheckExpiringSoon(anchor); err != nil {
			expiringAnchors = append(expiringAnchors, fmt.Sprintf("* %v %s %s", anchor.SerialNumber, anchor.Subject.CommonName, err))
		}
	}
	if len(expiringAnchors) > 0 {
		return fmt.Errorf("Anchors expiring soon:\n\t%s", strings.Join(expiringAnchors, "\n\t"))
	}

	// check cert validity
	if err := issuercerts.CheckCertValidityPeriod(cert.Certificate); err != nil {
		return fmt.Errorf("certificate is %s", err)
	}

	// check cert not expiring soon
	if err := issuercerts.CheckExpiringSoon(cert.Certificate); err != nil {
		return fmt.Errorf("certificate %s", err)
	}

	if err := cert.Verify(tls.CertificatesToPool(trustAnchors), identityName, time.Time{}); err != nil {
		return fmt.Errorf("cert is not issued by the trust anchor: %s", err)
	}

	return nil
}

func (hc *HealthChecker) checkMinReplicasAvailable(ctx context.Context) error {
	faulty := []string{}

	for _, component := range linkerdHAControlPlaneComponents {
		conf, err := hc.kubeAPI.AppsV1().Deployments(hc.ControlPlaneNamespace).Get(ctx, component, metav1.GetOptions{})
		if err != nil {
			return err
		}

		if conf.Status.AvailableReplicas <= 1 {
			faulty = append(faulty, component)
		}
	}

	if len(faulty) > 0 {
		return fmt.Errorf("not enough replicas available for %v", faulty)
	}
	return nil
}

func (hc *HealthChecker) issuerIdentity() string {
	return fmt.Sprintf("identity.%s.%s", hc.ControlPlaneNamespace, hc.linkerdConfig.Global.IdentityTrustDomain)
}

// Add adds an arbitrary checker. This should only be used for testing. For
// production code, pass in the desired set of checks when calling
// NewHealthChecker.
func (hc *HealthChecker) Add(categoryID CategoryID, description string, hintAnchor string, check func(context.Context) error) {
	hc.addCategory(
		category{
			id: categoryID,
			checkers: []checker{
				{
					description: description,
					check:       check,
					hintAnchor:  hintAnchor,
				},
			},
		},
	)
}

// addCategory is also for testing
func (hc *HealthChecker) addCategory(c category) {
	c.enabled = true
	hc.categories = append(hc.categories, c)
}

// RunChecks runs all configured checkers, and passes the results of each
// check to the observer. If a check fails and is marked as fatal, then all
// remaining checks are skipped. If at least one check fails, RunChecks returns
// false; if all checks passed, RunChecks returns true.  Checks which are
// designated as warnings will not cause RunCheck to return false, however.
func (hc *HealthChecker) RunChecks(observer CheckObserver) bool {
	success := true
	for _, c := range hc.categories {
		if c.enabled {
			for _, checker := range c.checkers {
				checker := checker // pin
				if checker.check != nil {
					if !hc.runCheck(c.id, &checker, observer) {
						if !checker.warning {
							success = false
						}
						if checker.fatal {
							return success
						}
					}
				}

				if checker.checkRPC != nil {
					if !hc.runCheckRPC(c.id, &checker, observer) {
						if !checker.warning {
							success = false
						}
						if checker.fatal {
							return success
						}
					}
				}
			}
		}
	}

	return success
}

func (hc *HealthChecker) runCheck(categoryID CategoryID, c *checker, observer CheckObserver) bool {
	for {
		ctx, cancel := context.WithTimeout(context.Background(), requestTimeout)
		defer cancel()
		err := c.check(ctx)
		if se, ok := err.(*SkipError); ok {
			log.Debugf("Skipping check: %s. Reason: %s", c.description, se.Reason)
			return true
		}

		checkResult := &CheckResult{
			Category:    categoryID,
			Description: c.description,
			HintAnchor:  c.hintAnchor,
			Warning:     c.warning,
		}
		if vs, ok := err.(*VerboseSuccess); ok {
			checkResult.Description = fmt.Sprintf("%s\n%s", checkResult.Description, vs.Message)
		} else if err != nil {
			checkResult.Err = &CategoryError{categoryID, err}
		}

		if checkResult.Err != nil && time.Now().Before(c.retryDeadline) {
			checkResult.Retry = true
			if !c.surfaceErrorOnRetry {
				checkResult.Err = errors.New("waiting for check to complete")
			}
			log.Debugf("Retrying on error: %s", err)

			observer(checkResult)
			time.Sleep(retryWindow)
			continue
		}

		observer(checkResult)
		return checkResult.Err == nil
	}
}

// runCheckRPC calls `c` which itself should make a gRPC call returning `*healthcheckPb.SelfCheckResponse`
// (which can contain multiple responses) or error.
// If that call returns an error, we send it to `observer` and return false.
// Otherwise, we send to `observer` a success message with `c.description` and then proceed to check the
// multiple responses contained in the response.
// We keep on retrying the same call until all the responses have an OK status
// (or until timeout/deadline is reached), sending a message to `observer` for each response,
// while making sure no duplicate messages are sent.
func (hc *HealthChecker) runCheckRPC(categoryID CategoryID, c *checker, observer CheckObserver) bool {
	observedResults := []CheckResult{}
	for {
		ctx, cancel := context.WithTimeout(context.Background(), requestTimeout)
		defer cancel()
		checkRsp, err := c.checkRPC(ctx)
		if se, ok := err.(*SkipError); ok {
			log.Debugf("Skipping check: %s. Reason: %s", c.description, se.Reason)
			return true
		}

		checkResult := &CheckResult{
			Category:    categoryID,
			Description: c.description,
			HintAnchor:  c.hintAnchor,
			Warning:     c.warning,
		}

		if vs, ok := err.(*VerboseSuccess); ok {
			checkResult.Description = fmt.Sprintf("%s\n%s", checkResult.Description, vs.Message)
		} else if err != nil {
			// errors at the gRPC-call level are not retried
			// but we do retry below if the response Status is not OK
			checkResult.Err = &CategoryError{categoryID, err}
			observer(checkResult)
			return false
		}

		// General description, only shown once.
		// The following calls to `observer()` track specific result entries.
		if !checkResult.alreadyObserved(observedResults) {
			observer(checkResult)
			observedResults = append(observedResults, *checkResult)
		}

		for _, check := range checkRsp.Results {
			checkResult.Err = nil
			checkResult.Description = fmt.Sprintf("[%s] %s", check.SubsystemName, check.CheckDescription)
			if check.Status != healthcheckPb.CheckStatus_OK {
				checkResult.Err = &CategoryError{categoryID, fmt.Errorf(check.FriendlyMessageToUser)}
				checkResult.Retry = time.Now().Before(c.retryDeadline)
				// only show the waiting message during retries,
				// and send the underlying error on the last try
				if !c.surfaceErrorOnRetry && checkResult.Retry {
					checkResult.Err = errors.New("waiting for check to complete")
				}
				observer(checkResult)
			} else if !checkResult.alreadyObserved(observedResults) {
				observer(checkResult)
			}
			observedResults = append(observedResults, *checkResult)
		}

		if checkResult.Retry {
			log.Debug("Retrying on error")
			time.Sleep(retryWindow)
			continue
		}

		return checkResult.Err == nil
	}
}

func (hc *HealthChecker) controlPlaneComponentsSelector() string {
	return fmt.Sprintf("%s,!%s", k8s.ControllerNSLabel, LinkerdCNIResourceLabel)
}

// PublicAPIClient returns a fully configured public API client. This client is
// only configured if the KubernetesAPIChecks and LinkerdAPIChecks are
// configured and run first.
func (hc *HealthChecker) PublicAPIClient() public.APIClient {
	return hc.apiClient
}

func (hc *HealthChecker) checkLinkerdConfigConfigMap(ctx context.Context) (string, *l5dcharts.Values, error) {
	configMap, values, err := FetchCurrentConfiguration(ctx, hc.kubeAPI, hc.ControlPlaneNamespace)
	if err != nil {
		return "", nil, err
	}

	return string(configMap.GetUID()), values, nil
}

// Checks whether the configuration of the linkerd-identity-issuer is correct. This means:
// 1. There is a config map present with identity context
// 2. The scheme in the identity context corresponds to the format of the issuer secret
// 3. The trust anchors (if scheme == kubernetes.io/tls) in the secret equal the ones in config
// 4. The certs and key are parsable
func (hc *HealthChecker) checkCertificatesConfig(ctx context.Context) (*tls.Cred, []*x509.Certificate, error) {
	_, values, err := FetchCurrentConfiguration(ctx, hc.kubeAPI, hc.ControlPlaneNamespace)
	if err != nil {
		return nil, nil, err
	}

	var data *issuercerts.IssuerCertData

	if values.Identity.Issuer.Scheme == "" || values.Identity.Issuer.Scheme == k8s.IdentityIssuerSchemeLinkerd {
		data, err = issuercerts.FetchIssuerData(ctx, hc.kubeAPI, values.Global.IdentityTrustAnchorsPEM, hc.ControlPlaneNamespace)
	} else {
		data, err = issuercerts.FetchExternalIssuerData(ctx, hc.kubeAPI, hc.ControlPlaneNamespace)
		// ensure trust anchors in config matches what's in the secret
		if data != nil && strings.TrimSpace(values.Global.IdentityTrustAnchorsPEM) != strings.TrimSpace(data.TrustAnchors) {
			errFormat := "IdentityContext.TrustAnchorsPem does not match %s in %s"
			err = fmt.Errorf(errFormat, k8s.IdentityIssuerTrustAnchorsNameExternal, k8s.IdentityIssuerSecretName)
		}
	}

	if err != nil {
		return nil, nil, err
	}

	issuerCreds, err := tls.ValidateAndCreateCreds(data.IssuerCrt, data.IssuerKey)
	if err != nil {
		return nil, nil, err
	}

	anchors, err := tls.DecodePEMCertificates(data.TrustAnchors)
	if err != nil {
		return nil, nil, err
	}

	return issuerCreds, anchors, nil
}

// FetchCurrentConfiguration retrieves the current Linkerd configuration
func FetchCurrentConfiguration(ctx context.Context, k kubernetes.Interface, controlPlaneNamespace string) (*corev1.ConfigMap, *l5dcharts.Values, error) {

	// Get the linkerd-config values if present
	configMap, configPb, err := FetchLinkerdConfigMap(ctx, k, controlPlaneNamespace)
	if err != nil {
		return nil, nil, err
	}

	if rawValues := configMap.Data["values"]; rawValues != "" {
		var fullValues l5dcharts.Values
		err = yaml.Unmarshal([]byte(rawValues), &fullValues)
		if err != nil {
			return nil, nil, err
		}
		return configMap, &fullValues, nil
	}

	// fall back to the older configMap
	// TODO: remove this once the newer config override secret becomes the default i.e 2.10
	return configMap, config.ToValues(configPb), nil
}

func (hc *HealthChecker) fetchProxyInjectorCaBundle(ctx context.Context) ([]*x509.Certificate, error) {
	mwh, err := hc.getProxyInjectorMutatingWebhook(ctx)
	if err != nil {
		return nil, err
	}

	caBundle, err := tls.DecodePEMCertificates(string(mwh.ClientConfig.CABundle))
	if err != nil {
		return nil, err
	}
	return caBundle, nil
}

func (hc *HealthChecker) fetchSpValidatorCaBundle(ctx context.Context) ([]*x509.Certificate, error) {

	vwc, err := hc.kubeAPI.AdmissionregistrationV1beta1().ValidatingWebhookConfigurations().Get(ctx, k8s.SPValidatorWebhookConfigName, metav1.GetOptions{})
	if err != nil {
		return nil, err
	}

	if len(vwc.Webhooks) != 1 {
		return nil, fmt.Errorf("expected 1 webhooks, found %d", len(vwc.Webhooks))
	}

	caBundle, err := tls.DecodePEMCertificates(string(vwc.Webhooks[0].ClientConfig.CABundle))
	if err != nil {
		return nil, err
	}
	return caBundle, nil
}

func (hc *HealthChecker) fetchTapCaBundle(ctx context.Context) ([]*x509.Certificate, error) {
	apiServiceClient, err := apiregistrationv1client.NewForConfig(hc.kubeAPI.Config)
	if err != nil {
		return nil, err
	}

	apiService, err := apiServiceClient.APIServices().Get(ctx, linkerdTapAPIServiceName, metav1.GetOptions{})
	if err != nil {
		return nil, err
	}

	caBundle, err := tls.DecodePEMCertificates(string(apiService.Spec.CABundle))
	if err != nil {
		return nil, err
	}
	return caBundle, nil
}

func (hc *HealthChecker) fetchCredsFromSecret(ctx context.Context, secretName string) (*tls.Cred, error) {
	secret, err := hc.kubeAPI.CoreV1().Secrets(hc.ControlPlaneNamespace).Get(ctx, secretName, metav1.GetOptions{})
	if err != nil {
		return nil, err
	}

	crt, ok := secret.Data[certKeyName]
	if !ok {
		return nil, fmt.Errorf("key %s needs to exist in secret %s", certKeyName, secretName)
	}

	key, ok := secret.Data[keyKeyName]
	if !ok {
		return nil, fmt.Errorf("key %s needs to exist in secret %s", keyKeyName, secretName)
	}

	cred, err := tls.ValidateAndCreateCreds(string(crt), string(key))
	if err != nil {
		return nil, err
	}

	return cred, nil
}

// this function can be removed in later versions, once eihter all webhook secrets are recreated for each update
// (see https://github.com/linkerd/linkerd2/issues/4813)
// or later releases are only expected to update from the new names.
func (hc *HealthChecker) fetchCredsFromOldSecret(ctx context.Context, secretName string) (*tls.Cred, error) {
	secret, err := hc.kubeAPI.CoreV1().Secrets(hc.ControlPlaneNamespace).Get(ctx, secretName, metav1.GetOptions{})
	if err != nil {
		return nil, err
	}

	crt, ok := secret.Data[certOldKeyName]
	if !ok {
		return nil, fmt.Errorf("key %s needs to exist in secret %s", certKeyName, secretName)
	}

	key, ok := secret.Data[keyOldKeyName]
	if !ok {
		return nil, fmt.Errorf("key %s needs to exist in secret %s", keyKeyName, secretName)
	}

	cred, err := tls.ValidateAndCreateCreds(string(crt), string(key))
	if err != nil {
		return nil, err
	}

	return cred, nil
}

// FetchLinkerdConfigMap retrieves the `linkerd-config` ConfigMap from
// Kubernetes and parses it into `linkerd2.config` protobuf.
// TODO: Consider a different package for this function. This lives in the
// healthcheck package because healthcheck depends on it, along with other
// packages that also depend on healthcheck. This function depends on both
// `pkg/k8s` and `pkg/config`, which do not depend on each other.
func FetchLinkerdConfigMap(ctx context.Context, k kubernetes.Interface, controlPlaneNamespace string) (*corev1.ConfigMap, *configPb.All, error) {
	cm, err := k.CoreV1().ConfigMaps(controlPlaneNamespace).Get(ctx, k8s.ConfigConfigMapName, metav1.GetOptions{})
	if err != nil {
		return nil, nil, err
	}

	configPB, err := config.FromConfigMap(cm.Data)
	if err != nil {
		return nil, nil, err
	}

	return cm, configPB, nil
}

// checkNamespace checks whether the given namespace exists, and returns an
// error if it does not match `shouldExist`.
func (hc *HealthChecker) checkNamespace(ctx context.Context, namespace string, shouldExist bool) error {
	exists, err := hc.kubeAPI.NamespaceExists(ctx, namespace)
	if err != nil {
		return err
	}
	if shouldExist && !exists {
		return fmt.Errorf("The \"%s\" namespace does not exist", namespace)
	}
	if !shouldExist && exists {
		return fmt.Errorf("The \"%s\" namespace already exists", namespace)
	}
	return nil
}

func (hc *HealthChecker) expectedRBACNames() []string {
	return []string{
		fmt.Sprintf("linkerd-%s-controller", hc.ControlPlaneNamespace),
		fmt.Sprintf("linkerd-%s-identity", hc.ControlPlaneNamespace),
		fmt.Sprintf("linkerd-%s-proxy-injector", hc.ControlPlaneNamespace),
		fmt.Sprintf("linkerd-%s-sp-validator", hc.ControlPlaneNamespace),
		fmt.Sprintf("linkerd-%s-tap", hc.ControlPlaneNamespace),
	}
}

func (hc *HealthChecker) checkRoles(ctx context.Context, shouldExist bool, namespace string, expectedNames []string, labelSelector string) error {
	options := metav1.ListOptions{
		LabelSelector: labelSelector,
	}
	crList, err := hc.kubeAPI.RbacV1().Roles(namespace).List(ctx, options)
	if err != nil {
		return err
	}

	objects := []runtime.Object{}

	for _, item := range crList.Items {
		item := item // pin
		objects = append(objects, &item)
	}

	return checkResources("Roles", objects, expectedNames, shouldExist)
}

func (hc *HealthChecker) checkRoleBindings(ctx context.Context, shouldExist bool, namespace string, expectedNames []string, labelSelector string) error {
	options := metav1.ListOptions{
		LabelSelector: labelSelector,
	}
	crbList, err := hc.kubeAPI.RbacV1().RoleBindings(namespace).List(ctx, options)
	if err != nil {
		return err
	}

	objects := []runtime.Object{}

	for _, item := range crbList.Items {
		item := item // pin
		objects = append(objects, &item)
	}

	return checkResources("RoleBindings", objects, expectedNames, shouldExist)
}

func (hc *HealthChecker) checkClusterRoles(ctx context.Context, shouldExist bool, expectedNames []string, labelSelector string) error {
	options := metav1.ListOptions{
		LabelSelector: labelSelector,
	}
	crList, err := hc.kubeAPI.RbacV1().ClusterRoles().List(ctx, options)
	if err != nil {
		return err
	}

	objects := []runtime.Object{}

	for _, item := range crList.Items {
		item := item // pin
		objects = append(objects, &item)
	}

	return checkResources("ClusterRoles", objects, expectedNames, shouldExist)
}

func (hc *HealthChecker) checkClusterRoleBindings(ctx context.Context, shouldExist bool, expectedNames []string, labelSelector string) error {
	options := metav1.ListOptions{
		LabelSelector: labelSelector,
	}
	crbList, err := hc.kubeAPI.RbacV1().ClusterRoleBindings().List(ctx, options)
	if err != nil {
		return err
	}

	objects := []runtime.Object{}

	for _, item := range crbList.Items {
		item := item // pin
		objects = append(objects, &item)
	}

	return checkResources("ClusterRoleBindings", objects, expectedNames, shouldExist)
}

func (hc *HealthChecker) isHA() bool {
	return hc.linkerdConfig.Global.HighAvailability
}

func (hc *HealthChecker) isHeartbeatDisabled() bool {
	return hc.linkerdConfig.DisableHeartBeat
}

func (hc *HealthChecker) checkServiceAccounts(ctx context.Context, saNames []string, ns, labelSelector string) error {
	options := metav1.ListOptions{
		LabelSelector: labelSelector,
	}
	saList, err := hc.kubeAPI.CoreV1().ServiceAccounts(ns).List(ctx, options)
	if err != nil {
		return err
	}

	objects := []runtime.Object{}

	for _, item := range saList.Items {
		item := item // pin
		objects = append(objects, &item)
	}

	return checkResources("ServiceAccounts", objects, saNames, true)
}

func (hc *HealthChecker) checkCustomResourceDefinitions(ctx context.Context, shouldExist bool) error {
	options := metav1.ListOptions{
		LabelSelector: hc.controlPlaneComponentsSelector(),
	}
	crdList, err := hc.kubeAPI.Apiextensions.ApiextensionsV1beta1().CustomResourceDefinitions().List(ctx, options)
	if err != nil {
		return err
	}

	objects := []runtime.Object{}
	for _, item := range crdList.Items {
		item := item // pin
		objects = append(objects, &item)
	}

	return checkResources("CustomResourceDefinitions", objects, []string{"serviceprofiles.linkerd.io"}, shouldExist)
}

func (hc *HealthChecker) getProxyInjectorMutatingWebhook(ctx context.Context) (*admissionRegistration.MutatingWebhook, error) {
	mwc, err := hc.kubeAPI.AdmissionregistrationV1beta1().MutatingWebhookConfigurations().Get(ctx, k8s.ProxyInjectorWebhookConfigName, metav1.GetOptions{})
	if err != nil {
		return nil, err
	}
	if len(mwc.Webhooks) != 1 {
		return nil, fmt.Errorf("expected 1 webhooks, found %d", len(mwc.Webhooks))
	}
	return &mwc.Webhooks[0], nil
}

func (hc *HealthChecker) getMutatingWebhookFailurePolicy(ctx context.Context) (*admissionRegistration.FailurePolicyType, error) {
	mwh, err := hc.getProxyInjectorMutatingWebhook(ctx)
	if err != nil {
		return nil, err
	}
	return mwh.FailurePolicy, nil
}

func (hc *HealthChecker) checkMutatingWebhookConfigurations(ctx context.Context, shouldExist bool) error {
	options := metav1.ListOptions{
		LabelSelector: hc.controlPlaneComponentsSelector(),
	}
	mwc, err := hc.kubeAPI.AdmissionregistrationV1beta1().MutatingWebhookConfigurations().List(ctx, options)
	if err != nil {
		return err
	}

	objects := []runtime.Object{}
	for _, item := range mwc.Items {
		item := item // pin
		objects = append(objects, &item)
	}

	return checkResources("MutatingWebhookConfigurations", objects, []string{k8s.ProxyInjectorWebhookConfigName}, shouldExist)
}

func (hc *HealthChecker) checkValidatingWebhookConfigurations(ctx context.Context, shouldExist bool) error {
	options := metav1.ListOptions{
		LabelSelector: hc.controlPlaneComponentsSelector(),
	}
	vwc, err := hc.kubeAPI.AdmissionregistrationV1beta1().ValidatingWebhookConfigurations().List(ctx, options)
	if err != nil {
		return err
	}

	objects := []runtime.Object{}
	for _, item := range vwc.Items {
		item := item // pin
		objects = append(objects, &item)
	}

	return checkResources("ValidatingWebhookConfigurations", objects, []string{k8s.SPValidatorWebhookConfigName}, shouldExist)
}

func (hc *HealthChecker) checkPodSecurityPolicies(ctx context.Context, shouldExist bool) error {
	options := metav1.ListOptions{
		LabelSelector: hc.controlPlaneComponentsSelector(),
	}
	psp, err := hc.kubeAPI.PolicyV1beta1().PodSecurityPolicies().List(ctx, options)
	if err != nil {
		return err
	}

	objects := []runtime.Object{}
	for _, item := range psp.Items {
		item := item // pin
		objects = append(objects, &item)
	}
	return checkResources("PodSecurityPolicies", objects, []string{fmt.Sprintf("linkerd-%s-control-plane", hc.ControlPlaneNamespace)}, shouldExist)
}

// MeshedPodIdentityData contains meshed pod details + trust anchors of the proxy
type MeshedPodIdentityData struct {
	Name      string
	Namespace string
	Anchors   string
}

// GetMeshedPodsIdentityData obtains the identity data (trust anchors) for all meshed pods
func GetMeshedPodsIdentityData(ctx context.Context, api kubernetes.Interface, dataPlaneNamespace string) ([]MeshedPodIdentityData, error) {
	podList, err := api.CoreV1().Pods(dataPlaneNamespace).List(ctx, metav1.ListOptions{LabelSelector: k8s.ControllerNSLabel})
	if err != nil {
		return nil, err
	}
	if len(podList.Items) == 0 {
		return nil, nil
	}
	pods := []MeshedPodIdentityData{}
	for _, pod := range podList.Items {
		for _, containerSpec := range pod.Spec.Containers {
			if containerSpec.Name != k8s.ProxyContainerName {
				continue
			}
			for _, envVar := range containerSpec.Env {
				if envVar.Name != identity.EnvTrustAnchors {
					continue
				}
				pods = append(pods, MeshedPodIdentityData{
					pod.Name, pod.Namespace, strings.TrimSpace(envVar.Value),
				})
			}
		}
	}
	return pods, nil
}

func (hc *HealthChecker) checkDataPlaneProxiesCertificate(ctx context.Context) error {
	meshedPods, err := GetMeshedPodsIdentityData(ctx, hc.kubeAPI.Interface, hc.DataPlaneNamespace)
	if err != nil {
		return err
	}

	_, values, err := FetchCurrentConfiguration(ctx, hc.kubeAPI, hc.ControlPlaneNamespace)
	if err != nil {
		return err
	}

	trustAnchorsPem := values.Global.IdentityTrustAnchorsPEM
	offendingPods := []string{}
	for _, pod := range meshedPods {
		if strings.TrimSpace(pod.Anchors) != strings.TrimSpace(trustAnchorsPem) {
			if hc.DataPlaneNamespace == "" {
				offendingPods = append(offendingPods, fmt.Sprintf("* %s/%s", pod.Namespace, pod.Name))
			} else {
				offendingPods = append(offendingPods, fmt.Sprintf("* %s", pod.Name))
			}
		}
	}
	if len(offendingPods) == 0 {
		return nil
	}
	return fmt.Errorf("Some pods do not have the current trust bundle and must be restarted:\n\t%s", strings.Join(offendingPods, "\n\t"))
}

func checkResources(resourceName string, objects []runtime.Object, expectedNames []string, shouldExist bool) error {
	if !shouldExist {
		if len(objects) > 0 {
			resources := []Resource{}
			for _, obj := range objects {
				m, err := meta.Accessor(obj)
				if err != nil {
					return err
				}

				res := Resource{name: m.GetName()}
				gvks, _, err := k8s.ObjectKinds(obj)
				if err == nil && len(gvks) > 0 {
					res.groupVersionKind = gvks[0]
				}
				resources = append(resources, res)
			}
			return &ResourceError{resourceName, resources}
		}
		return nil
	}

	expected := map[string]bool{}
	for _, name := range expectedNames {
		expected[name] = false
	}

	for _, obj := range objects {
		metaObj, err := meta.Accessor(obj)
		if err != nil {
			return err
		}

		if _, ok := expected[metaObj.GetName()]; ok {
			expected[metaObj.GetName()] = true
		}
	}

	missing := []string{}
	for name, found := range expected {
		if !found {
			missing = append(missing, name)
		}
	}
	if len(missing) > 0 {
		sort.Strings(missing)
		return fmt.Errorf("missing %s: %s", resourceName, strings.Join(missing, ", "))
	}

	return nil
}

func (hc *HealthChecker) getDataPlanePods(ctx context.Context) ([]*pb.Pod, error) {
	req := &pb.ListPodsRequest{}
	if hc.DataPlaneNamespace != "" {
		req.Selector = &pb.ResourceSelection{
			Resource: &pb.Resource{
				Namespace: hc.DataPlaneNamespace,
			},
		}
	}

	resp, err := hc.apiClient.ListPods(ctx, req)
	if err != nil {
		return nil, err
	}

	pods := make([]*pb.Pod, 0)
	for _, pod := range resp.GetPods() {
		if pod.ControllerNamespace == hc.ControlPlaneNamespace {
			pods = append(pods, pod)
		}
	}

	return pods, nil
}

func (hc *HealthChecker) checkCanPerformAction(ctx context.Context, api *k8s.KubernetesAPI, verb, namespace, group, version, resource string) error {
	if api == nil {
		// we should never get here
		return fmt.Errorf("unexpected error: Kubernetes ClientSet not initialized")
	}

	return k8s.ResourceAuthz(
		ctx,
		api,
		namespace,
		verb,
		group,
		version,
		resource,
		"",
	)
}

func (hc *HealthChecker) checkHAMetadataPresentOnKubeSystemNamespace(ctx context.Context) error {
	ns, err := hc.kubeAPI.CoreV1().Namespaces().Get(ctx, "kube-system", metav1.GetOptions{})
	if err != nil {
		return err
	}

	val, ok := ns.Labels[k8s.AdmissionWebhookLabel]
	if !ok || val != "disabled" {
		return fmt.Errorf("kube-system namespace needs to have the label %s: disabled if injector webhook failure policy is Fail", k8s.AdmissionWebhookLabel)
	}

	return nil
}

func (hc *HealthChecker) checkCanCreate(ctx context.Context, namespace, group, version, resource string) error {
	return hc.checkCanPerformAction(ctx, hc.kubeAPI, "create", namespace, group, version, resource)
}

func (hc *HealthChecker) checkCanCreateNonNamespacedResources(ctx context.Context) error {
	var errs []string
	dryRun := metav1.CreateOptions{DryRun: []string{metav1.DryRunAll}}

	// Iterate over all resources in install manifest
	installManifestReader := strings.NewReader(hc.Options.InstallManifest)
	yamlReader := yamlDecoder.NewYAMLReader(bufio.NewReader(installManifestReader))
	for {
		// Read single object YAML
		objYAML, err := yamlReader.Read()
		if err == io.EOF {
			break
		}
		if err != nil {
			return fmt.Errorf("error reading install manifest: %v", err)
		}

		// Create unstructured object from YAML
		objMap := map[string]interface{}{}
		err = yaml.Unmarshal(objYAML, &objMap)
		if err != nil {
			return fmt.Errorf("error unmarshaling yaml object %s: %v", objYAML, err)
		}
		if len(objMap) == 0 {
			// Ignore header blocks with only comments
			continue
		}
		obj := &unstructured.Unstructured{Object: objMap}

		// Skip namespaced resources (dry-run requires namespace to exist)
		if obj.GetNamespace() != "" {
			continue
		}
		// Attempt to create resource using dry-run
		resource, _ := meta.UnsafeGuessKindToResource(obj.GroupVersionKind())
		_, err = hc.kubeAPI.DynamicClient.Resource(resource).Create(ctx, obj, dryRun)
		if err != nil {
			errs = append(errs, fmt.Sprintf("cannot create %s/%s: %v", obj.GetKind(), obj.GetName(), err))
		}
	}

	if len(errs) > 0 {
		return errors.New(strings.Join(errs, "\n    "))
	}
	return nil
}

func (hc *HealthChecker) checkCanGet(ctx context.Context, namespace, group, version, resource string) error {
	return hc.checkCanPerformAction(ctx, hc.kubeAPI, "get", namespace, group, version, resource)
}

func (hc *HealthChecker) checkAPIService(ctx context.Context, serviceName string) error {
	apiServiceClient, err := apiregistrationv1client.NewForConfig(hc.kubeAPI.Config)
	if err != nil {
		return err
	}

	apiStatus, err := apiServiceClient.APIServices().Get(ctx, serviceName, metav1.GetOptions{})
	if err != nil {
		return err
	}

	for _, condition := range apiStatus.Status.Conditions {
		if condition.Type == "Available" {
			if condition.Status == "True" {
				return nil
			}
			return fmt.Errorf("%s: %s", condition.Reason, condition.Message)
		}
	}

	return fmt.Errorf("%s service not available", linkerdTapAPIServiceName)
}

func (hc *HealthChecker) checkCapability(ctx context.Context, cap string) error {
	if hc.kubeAPI == nil {
		// we should never get here
		return fmt.Errorf("unexpected error: Kubernetes ClientSet not initialized")
	}

	pspList, err := hc.kubeAPI.PolicyV1beta1().PodSecurityPolicies().List(ctx, metav1.ListOptions{})
	if err != nil {
		return err
	}

	if len(pspList.Items) == 0 {
		// no PodSecurityPolicies found, assume PodSecurityPolicy admission controller is disabled
		return nil
	}

	// if PodSecurityPolicies are found, validate one exists that:
	// 1) permits usage
	// AND
	// 2) provides the specified capability
	for _, psp := range pspList.Items {
		err := k8s.ResourceAuthz(
			ctx,
			hc.kubeAPI,
			"",
			"use",
			"policy",
			"v1beta1",
			"podsecuritypolicies",
			psp.GetName(),
		)
		if err == nil {
			for _, capability := range psp.Spec.AllowedCapabilities {
				if capability == "*" || string(capability) == cap {
					return nil
				}
			}
		}
	}

	return fmt.Errorf("found %d PodSecurityPolicies, but none provide %s, proxy injection will fail if the PSP admission controller is running", len(pspList.Items), cap)
}
func (hc *HealthChecker) checkExtensionAPIServerAuthentication(ctx context.Context) error {
	if hc.kubeAPI == nil {
		return fmt.Errorf("unexpected error: Kubernetes ClientSet not initialized")
	}
	m, err := hc.kubeAPI.CoreV1().ConfigMaps(metav1.NamespaceSystem).Get(ctx, k8s.ExtensionAPIServerAuthenticationConfigMapName, metav1.GetOptions{})
	if err != nil {
		return err
	}
	if v, exists := m.Data[k8s.ExtensionAPIServerAuthenticationRequestHeaderClientCAFileKey]; !exists || v == "" {
		return fmt.Errorf("--%s is not configured", k8s.ExtensionAPIServerAuthenticationRequestHeaderClientCAFileKey)
	}
	return nil
}
func (hc *HealthChecker) checkClockSkew(ctx context.Context) error {
	if hc.kubeAPI == nil {
		// we should never get here
		return fmt.Errorf("unexpected error: Kubernetes ClientSet not initialized")
	}

	var clockSkewNodes []string

	nodeList, err := hc.kubeAPI.CoreV1().Nodes().List(ctx, metav1.ListOptions{})
	if err != nil {
		return err
	}

	for _, node := range nodeList.Items {
		for _, condition := range node.Status.Conditions {
			// we want to check only KubeletReady condition and only execute if the node is ready
			if condition.Type == corev1.NodeReady && condition.Status == corev1.ConditionTrue {
				since := time.Since(condition.LastHeartbeatTime.Time)
				if (since > AllowedClockSkew) || (since < -AllowedClockSkew) {
					clockSkewNodes = append(clockSkewNodes, node.Name)
				}
			}
		}
	}

	if len(clockSkewNodes) > 0 {
		return fmt.Errorf("clock skew detected for node(s): %s", strings.Join(clockSkewNodes, ", "))
	}

	return nil
}

func (cr *CheckResult) alreadyObserved(previousResults []CheckResult) bool {
	for _, result := range previousResults {
		if result.Description == cr.Description && result.Err == cr.Err {
			return true
		}
	}
	return false
}

// getPodStatuses returns a map of all Linkerd container statuses:
// component =>
//   pod name =>
//     container statuses
// "controller" =>
//   "linkerd-controller-6f78cbd47-bc557" =>
//     [destination status, public-api status, ...]
func getPodStatuses(pods []corev1.Pod) map[string]map[string][]corev1.ContainerStatus {
	statuses := make(map[string]map[string][]corev1.ContainerStatus)

	for _, pod := range pods {
		if pod.Status.Phase == corev1.PodRunning && strings.HasPrefix(pod.Name, "linkerd-") {
			parts := strings.Split(pod.Name, "-")
			// All control plane pods should have a name that results in at least 4
			// substrings when string.Split on '-'
			if len(parts) >= 4 {
				name := strings.Join(parts[1:len(parts)-2], "-")
				if _, found := statuses[name]; !found {
					statuses[name] = make(map[string][]corev1.ContainerStatus)
				}
				statuses[name][pod.Name] = pod.Status.ContainerStatuses
			}
		}
	}

	return statuses
}

const running = "Running"

func validateControlPlanePods(pods []corev1.Pod) error {
	statuses := getPodStatuses(pods)

	names := []string{"controller", "identity", "sp-validator", "web", "tap"}
	// TODO: deprecate this when we drop support for checking pre-default proxy-injector control-planes
	if _, found := statuses["proxy-injector"]; found {
		names = append(names, "proxy-injector")
	}

	for _, name := range names {
		pods, found := statuses[name]
		if !found {
			return fmt.Errorf("No running pods for \"linkerd-%s\"", name)
		}
		var err error
		var ready bool
		for pod, containers := range pods {
			containersReady := true
			for _, container := range containers {
				if !container.Ready {
					// TODO: Save this as a warning, allow check to pass but let the user
					// know there is at least one pod not ready. This might imply
					// restructuring health checks to allow individual checks to return
					// either fatal or warning, rather than setting this property at
					// compile time.
					err = fmt.Errorf("pod/%s container %s is not ready", pod, container.Name)
					containersReady = false
				}
			}
			if containersReady {
				// at least one pod has all containers ready
				ready = true
				break
			}
		}
		if !ready {
			return err
		}
	}

	return nil
}

func checkContainerRunning(pods []corev1.Pod, container string) error {
	statuses := getPodStatuses(pods)
	if _, ok := statuses[container]; !ok {
		for _, pod := range pods {
			podStatus := k8s.GetPodStatus(pod)
			if podStatus != running {
				return fmt.Errorf("%s status is %s", pod.Name, podStatus)
			}
		}
		return fmt.Errorf("No running pods for \"%s\"", container)
	}
	return nil
}

func validateDataPlanePods(pods []*pb.Pod, targetNamespace string) error {
	if len(pods) == 0 {
		msg := fmt.Sprintf("No \"%s\" containers found", k8s.ProxyContainerName)
		if targetNamespace != "" {
			msg += fmt.Sprintf(" in the \"%s\" namespace", targetNamespace)
		}
		return fmt.Errorf(msg)
	}

	for _, pod := range pods {
		if pod.Status != "Running" && pod.Status != "Evicted" {
			return fmt.Errorf("The \"%s\" pod is not running",
				pod.Name)
		}

		if !pod.ProxyReady {
			return fmt.Errorf("The \"%s\" container in the \"%s\" pod is not ready",
				k8s.ProxyContainerName, pod.Name)
		}
	}

	return nil
}

func validateDataPlanePodReporting(pods []*pb.Pod) error {
	notInPrometheus := []string{}

	for _, p := range pods {
		// the `Added` field indicates the pod was found in Prometheus
		if !p.Added {
			notInPrometheus = append(notInPrometheus, p.Name)
		}
	}

	errMsg := ""
	if len(notInPrometheus) > 0 {
		errMsg = fmt.Sprintf("Data plane metrics not found for %s.", strings.Join(notInPrometheus, ", "))
	}

	if errMsg != "" {
		return fmt.Errorf(errMsg)
	}

	return nil
}

func checkUnschedulablePods(pods []corev1.Pod) error {
	var errors []string
	for _, pod := range pods {
		for _, condition := range pod.Status.Conditions {
			if condition.Reason == corev1.PodReasonUnschedulable {
				errors = append(errors, fmt.Sprintf("%s: %s", pod.Name, condition.Message))
			}
		}
	}

	if len(errors) > 0 {
		return fmt.Errorf("%s", strings.Join(errors, "\n    "))
	}

	return nil
}

func checkControlPlaneReplicaSets(rst []appsv1.ReplicaSet) error {
	var errors []string
	for _, rs := range rst {
		for _, r := range rs.Status.Conditions {
			if r.Type == appsv1.ReplicaSetReplicaFailure && r.Status == corev1.ConditionTrue {
				errors = append(errors, fmt.Sprintf("%s: %s", r.Reason, r.Message))
			}
		}
	}

	if len(errors) > 0 {
		return fmt.Errorf("%s", strings.Join(errors, "\n   "))
	}

	return nil
}