feat: #1245 [proposal] Caching member cluster resources for Karmada
Signed-off-by: huntsman_ly <huntsman_ly@sina.com>
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huntsman_ly
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title: Caching member cluster resources for Karmada
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authors:
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- "@huntsman-li"
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- "@liys87x"
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reviewers:
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approvers:
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creation-date: 2022-02-14
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---
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# Caching member cluster resources for Karmada
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## Summary
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Provides a caching layer for Karmada to cache (member clusters) Kubernetes resources.
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## Motivation
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### Goals
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- Accelerates resource requests processing speed across regions
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- Provides a cross-cluster resource view
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- Compatible with (multi-cluster) multiple kubernetes resource versions
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- Unified resource requests entries
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- Reduces API server pressure of member clusters
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### Non-Goals
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## Proposal
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### User Stories (Optional)
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#### Story 1
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Imagine that we have a cross-region application that needs to run in multiple regions in order to provide service capabilities nearby. We achieve this by deploying a Kubernetes cluster in each region.
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Goals:
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- Get the distribution of the application in different clusters.
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- Get resource information across clusters through a unified endpoint.
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- Accelerate processing speed of resource requests across regions.
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- Get resources in multiple clusters by labels.
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## Design Details
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### Define the scope of the cached resource
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#### New ClusterCache API
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We propose a new CR in `cluster.karmada.io` group.
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```golang
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package v1alpha1
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import (
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corev1 "k8s.io/api/core/v1"
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metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
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)
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//+kubebuilder:object:root=true
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//+kubebuilder:subresource:status
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// ClusterCache is the Schema for the cluster cache API
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type ClusterCache struct {
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metav1.TypeMeta `json:",inline"`
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metav1.ObjectMeta `json:"metadata,omitempty"`
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Spec ClusterCacheSpec `json:"spec,omitempty"`
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Status ClusterCacheStatus `json:"status,omitempty"`
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}
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// ClusterCacheSpec defines the desired state of ClusterCache
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type ClusterCacheSpec struct {
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// ClusterSelectors represents the filter to select clusters.
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// +required
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ClusterSelectors []ClusterSelector `json:"clusterSelectors"`
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// ResourceSelectors used to select resources.
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// +required
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ResourceSelectors []ResourceSelector `json:"resourceSelectors"`
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// StatusUpdatePeriodSeconds is the period to update the status of the resource.
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// default is 10s.
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// +optional
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StatusUpdatePeriodSeconds uint32 `json:"statusUpdatePeriodSeconds,omitempty"`
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}
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// ClusterAffinity represents the filter to select clusters.
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type ClusterSelector struct {
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// LabelSelector is a filter to select member clusters by labels.
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// If non-nil and non-empty, only the clusters match this filter will be selected.
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// +optional
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LabelSelector *metav1.LabelSelector `json:"labelSelector,omitempty"`
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// FieldSelector is a filter to select member clusters by fields.
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// If non-nil and non-empty, only the clusters match this filter will be selected.
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// +optional
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FieldSelector *FieldSelector `json:"fieldSelector,omitempty"`
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// ClusterNames is the list of clusters to be selected.
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// +optional
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ClusterNames []string `json:"clusterNames,omitempty"`
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// ExcludedClusters is the list of clusters to be ignored.
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// +optional
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ExcludeClusters []string `json:"exclude,omitempty"`
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}
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// FieldSelector is a field filter.
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type FieldSelector struct {
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// A list of field selector requirements.
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MatchExpressions []corev1.NodeSelectorRequirement `json:"matchExpressions,omitempty"`
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}
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// ResourceSelector the resources will be selected.
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type ResourceSelector struct {
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// APIVersion represents the API version of the target resources.
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// +required
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APIVersion string `json:"apiVersion"`
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// Kind represents the Kind of the target resources.
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// +required
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Kind string `json:"kind"`
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// Namespace of the target resource.
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// Default is empty, which means all namespaces.
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// +optional
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Namespace string `json:"namespace,omitempty"`
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}
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// ClusterCacheStatus defines the observed state of ClusterCache
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type ClusterCacheStatus struct {
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// +optional
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Resources []ResourceStatusRef `json:"resources,omitempty"`
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// +optional
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StartTime *metav1.Time `json:"startTime,omitempty"`
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}
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type ResourceStatusRef struct {
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// +required
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Cluster string `json:"cluster"`
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// +optional
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APIVersion string `json:"apiVersion,omitempty"`
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// +required
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Kind string `json:"kind"`
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// +optional
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Namespace string `json:"namespace,omitempty"`
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// +required
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State CachePhase `json:"state"`
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// +required
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TotalNum int32 `json:"totalNum"`
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// +required
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UpdateTime *metav1.Time `json:"updateTime"`
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}
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// CachePhase is the current state of the cache
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// +enum
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type CachePhase string
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// These are the valid statuses of cache.
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const (
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CacheRunning CachePhase = "Running"
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CacheFailed CachePhase = "Failed"
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CacheUnknown CachePhase = "Unknown"
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)
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type ResourceStateRef struct {
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// +required
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Phase CachePhase `json:"phase"`
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// +optional
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Reason string `json:"reason"`
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}
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//+kubebuilder:object:root=true
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// ClusterCacheList contains a list of ClusterCache
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type ClusterCacheList struct {
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metav1.TypeMeta `json:",inline"`
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metav1.ListMeta `json:"metadata,omitempty"`
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Items []ClusterCache `json:"items"`
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}
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func init() {
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SchemeBuilder.Register(&ClusterCache{}, &ClusterCacheList{})
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}
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```
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#### Example
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The following example shows how to create a ClusterCache CRD.
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```yaml
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apiVersion: clustercaches.karmada.io/v1alpha1
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kind: ClusterCache
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metadata:
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name: clustercache-sample
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spec:
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clusterSelectors:
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- clusterNames:
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- member1
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- member2
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- member3
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resourceSelectors:
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- kind: Pod
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- kind: Ingress
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apiVersion: networking.k8s.io/v1
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- kind: DaemonSet
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namespace: kube-system
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- kind: Deployment
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status:
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startTime: "2020-05-01T00:00:00Z"
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resources:
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- cluster: member1
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kind: Pod
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totalNum: 700
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state:
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phase: Running
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updateTime: "2022-01-01T00:00:00Z"
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- cluster: member1
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kind: Ingress
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totalNum: 0
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state:
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phase: Failed
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reason: the server doesn't have a resource type ingresses
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updateTime: "2022-01-01T00:00:00Z"
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```
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### Test Plan
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