istio.io/content/docs/concepts/security/index.md

title	description	weight	keywords	aliases
Security	Describes Istio's authorization and authentication functionality.	30	security authentication authorization rbac access-control	/docs/concepts/network-and-auth/auth.html /docs/concepts/security/authn-policy/ /docs/concepts/security/mutual-tls/ /docs/concepts/security/rbac/

Istio aims to enhance the security of microservices and their communication without requiring service code changes. It is responsible for:

• Providing each service with a strong identity that represents its role to enable interoperability across clusters and clouds

• Securing service to service communication and end-user to service communication

• Providing a key management system to automate key and certificate generation, distribution, rotation, and revocation

The following diagram shows Istio's security architecture, which includes three primary components: identity, key management, and communication security. The diagram shows how to use Istio to secure the service-to-service communication between the frontend service running as the frontend-team service account and the backend service running as the backend-team service account. Istio supports services running on Kubernetes containers, virtual machines, and bare-metal machines.

{{< image width="60%" ratio="52.44%" link="./auth.svg" alt="Components making up the Istio security model." caption="Istio Security Architecture" >}}

As illustrated in the diagram, Istio uses secret volume mounts to deliver keys and certificates from Citadel to Kubernetes containers. For services running on VMs or bare-metal machines, we introduce a node agent, which is a process running on each VM or bare-metal machine. The node agent generates the private key and the CSR (Certificate Signing Request) locally, sends the CSR to Citadel for signing, and delivers the generated certificate together with the private key to Envoy.

Mutual TLS authentication

Identity

Istio uses Kubernetes service accounts to identify who runs the service:

• A service account in Istio has the format: spiffe://\<_domain_\>/ns/\<_namespace_>/sa/\<_serviceaccount_\>.

  • Replace _domain_ with _cluster.local_. We will support customization of domain in the near future.
  • Replace _namespace_ with the namespace of the Kubernetes service account.
  • Replace _serviceaccount_ with the Kubernetes service account name.

• A service account is the identity or role a workload runs as. The service account represents that workload's privileges. For systems requiring strong security, neither a random string, such as a service name, label, etc., nor the deployed binary should identify the amount of privilege for a workload. For example, let's say we have a workload pulling data from a multi-tenant database. If Alice runs this workload, she pulls a different set of data than if Bob runs this workload.

• To enable strong security policies, service accounts offer the flexibility to identify a machine, a user, a workload, or a group of workloads. Different workloads can even run as the same service account.

• The service account a workload runs as won't change during the lifetime of the workload.

• With domain name constraint, you can ensure service account uniqueness.

Communication security

Istio tunnels service-to-service communication through the client side Envoy and the server side Envoy. Istio secures end-to-end communication via:

• Local TCP connections between the service and Envoy.

• Mutual TLS connections between proxies.

• Secure Naming: during the handshake process, the client side Envoy checks that the service account the server side certificate provided is allowed to run the target service.

Key management

Istio supports services running on Kubernetes pods, virtual machines, and bare-metal machines. We use different key provisioning mechanisms for each scenario.

For services running on Kubernetes pods, the per-cluster Citadel, acting as Certificate Authority, automates the key and certificate management process. Citadel mainly performs four critical operations:

• Generate a SPIFFE key and certificate pair for each service account

• Distribute a key and certificate pair to each pod according to the service account

• Rotate keys and certificates periodically

• Revoke a specific key and certificate pair when necessary

For services running on VMs or bare-metal machines, Citadel performs the above four operations together with node agents.

Workflow

The Istio security workflow consists of two phases: deployment and runtime. The deployment phase is different for the workflow in Kubernetes and for the workflow in VMs or bare-metal machines. However, once the key and certificate are deployed, the runtime phase is the same. The following sections briefly cover the workflow.

Deployment phase in Kubernetes

1. Citadel watches the Kubernetes API Server.

2. Citadel creates a SPIFFE key and certificate pair for each of the existing and new service accounts.

3. Citadel sends them to the API Server.

4. When a pod is created, the API Server mounts the key and certificate pair according to the service account using Kubernetes secrets.

5. Pilot generates the configuration file with the proper key, certificate, and secure naming information, which defines what service account(s) can run a certain service, and passes the configuration on to Envoy.

Deployment phase in VMs or bare-metal Machines

1. Citadel creates a gRPC service to take the CSR.

2. The node agent creates the private key and CSR

3. The node agent sends the CSR to Citadel for signing.

4. Citadel validates the credentials carried in the CSR

5. Citadel signs the CSR to generate the certificate.

6. The node agent sends both, the certificate received from Citadel and the private key, to Envoy.

7. The above CSR process repeats periodically for rotation.

Runtime phase

1. The outbound traffic from a client service is rerouted to its local Envoy.

2. The client side Envoy starts a mutual TLS handshake with the server side Envoy. During the handshake, it also does a secure naming check to verify that the service account presented in the server certificate can run the server service.

3. The client side Envoy and the server side Envoy establish a mutual TLS connection.

4. The client side Envoy forwards the traffic to the server side Envoy

5. The server side Envoy forwards the traffic to the server service through local TCP connections.

Best practices

In this section, we provide a few deployment guidelines and discuss a real-world scenario.

Deployment guidelines

If there are multiple service operators, a.k.a. SREs), deploying different services in a medium- or large-size cluster, we recommend creating a separate namespace for each SRE team to isolate their access. For example, you can create a team1-ns namespace for team1, and team2-ns namespace for team2, such that both teams can't access each other's services.

{{< warning_icon >}} If Citadel is compromised, all its managed keys and certificates in the cluster may be exposed. We strongly recommend running Citadel in a dedicated namespace, for example istio-citadel-ns, to restrict access to the cluster to only administrators.

Example

Let us consider a three-tier application with three services: photo-frontend, photo-backend, and datastore. The photo SRE team manages the photo-frontend and photo-backend services while the datastore SRE team manages the datastore service. The photo-frontend can access photo-backend, and the photo-backend service can access datastore. However, the photo-frontend service cannot access datastore.

In this scenario, a cluster administrator creates three namespaces: istio-citadel-ns, photo-ns, and datastore-ns. The administrator has access to all namespaces and each team only has access to its own namespace. The photo SRE team creates two service accounts to run photo-frontend and photo-backend respectively in the photo-ns namespace. The datastore SRE team creates one service account to run the datastore service in the datastore-ns namespace. Moreover, we need to enforce the service access control in Istio Mixer such that photo-frontend cannot access datastore.

In this setup, Citadel can provide both key management and certificate management for all namespaces and isolate microservice deployments from each other.

Authentication

Istio provides two types of authentication:

• Transport authentication, also known as service-to-service authentication: verifies the direct client making the connection. Istio offers mutual TLS as a full stack solution for transport authentication. You can easily turn on this feature without requiring service code changes. This solution:

  • Provides each service with a strong identity representing its role to enable interoperability across clusters and clouds.
  • Secures service-to-service communication and end-user-to-service communication.
  • Provides a key management system to automate key and certificate generation, distribution, rotation, and revocation.

• Origin authentication, also known as end-user authentication: verifies the original client making the request as an end-user or device. Istio supports authentication with JSON Web Token (JWT) validation.

Authentication architecture

You can specify authentication requirements for services receiving requests in an Istio mesh using authentication policies. The mesh operator uses .yaml files to specify the policies. The policies are saved in the Istio configuration storage once deployed. Pilot, the Istio controller, watches the configuration storage. Upon any policy changes, Pilot translates the new policy to the appropriate configuration telling the Envoy sidecar proxy how to perform the required authentication mechanisms. Pilot may fetch the public key and attach it to the configuration for JWT validation. Alternatively, Pilot provides the path to the keys and certificates the Istio system manages and installs them to the application pod for mutual TLS. You can find more info in the PKI and identity section. Istio sends configurations to the targeted endpoints asynchronously. Once the proxy receives the configuration, the new authentication requirement takes effect immediately on that pod.

Client services, those that send requests, are responsible for following the necessary authentication mechanism. For origin authentication (JWT), the application is responsible for acquiring and attaching the JWT credential to the request. For mutual TLS, Istio provides a destination rule. The operator can use the destination rule to instruct client proxies to make initial connections using TLS with the certificates expected on the server side. You can find out more about how mutual TLS works in Istio in PKI and identity section.

{{< image width="60%" ratio="67.12%" link="./authn.svg" caption="Authentication Architecture" >}}

Istio outputs identities with both types of authentication, as well as other claims in the credential if applicable, to the next layer: authorization. Additionally, operators can specify which identity, either from transport or origin authentication, should Istio use as ‘the principal’.

Authentication policies

This section provides more details about how Istio authentication policies work. As you’ll remember from the Architecture section, authentication policies apply to requests that a service receives. To specify client-side authentication rules in mutual TLS, you need to specify the TLSSettings in the DestinationRule. You can find more information in our TLS settings reference docs. Like other Istio configuration, you can specify authentication policies in .yaml files. You deploy policies using kubectl.

The following example authentication policy specifies that transport authentication for the reviews service must use mutual TLS:

{{< text yaml >}} apiVersion: "authentication.istio.io/v1alpha1" kind: "Policy" metadata: name: "reviews" spec: targets:

• name: reviews peers:
• mtls: {} {{< /text >}}

Policy storage scope

Istio can store authentication policies in namespace-scope or mesh-scope storage:

• Mesh-scope policy is specified with a value of "MeshPolicy" for the kind field and the name "default". For example:

  {{< text yaml >}} apiVersion: "authentication.istio.io/v1alpha1" kind: "MeshPolicy" metadata: name: "default" spec: peers: - mtls: {} {{< /text >}}

• Namespace-scope policy is specified with a value of "Policy" for the kind field and a specified namespace. If unspecified, the default namespace is used. For example for namespace ns1:

  {{< text yaml >}} apiVersion: "authentication.istio.io/v1alpha1" kind: "Policy" metadata: name: "default" namespace: "ns1" spec: peers: - mtls: {} {{< /text >}}

Policies in the namespace-scope storage can only affect services in the same namespace. Policies in mesh-scope can affect all services in the mesh. To prevent conflict and misuse, only one policy can be defined in mesh-scope storage. That policy must be named default and have an empty targets: section. You can find more information on our target selectors section.

Kubernetes currently implements the Istio configuration on Custom Resource Definitions (CRDs). These CRDs correspond to namespace-scope and cluster-scope CRDs and automatically inherit access protection via the Kubernetes RBAC. You can read more on the Kubernetes CRD documentation

Target selectors

An authentication policy’s targets specify the service or services to which the policy applies. The following example shows a targets: section specifying that the policy applies to:

• The product-page service on any port.
• The reviews service on port 9000.

{{< text yaml >}} targets:

• name: product-page
• name: reviews ports:
  • number: 9000 {{< /text >}}

If you don't provide a targets: section, Istio matches the policy to all services in the storage scope of the policy. Thus, the targets: section can help you specify the scope of the policies:

• Mesh-wide policy: A policy defined in the mesh-scope storage with no target selector section. There can be at most one mesh-wide policy in the mesh.

• Namespace-wide policy: A policy defined in the namespace-scope storage with name default and no target selector section. There can be at most one namespace-wide policy per namespace.

• Service-specific policy: a policy defined in the namespace-scope storage, with non-empty target selector section. A namespace can have zero, one, or many service-specific policies.

For each service, Istio applies the narrowest matching policy. The order is: service-specific > namespace-wide > mesh-wide. If more than one service-specific policy matches a service, Istio selects one of them at random. Operators must avoid such conflicts when configuring their policies.

To enforce uniqueness for mesh-wide and namespace-wide policies, Istio accepts only one authentication policy per mesh and one authentication policy per namespace. Istio also requires mesh-wide and namespace-wide policies to have the specific name default.

Transport authentication

The peers: section defines the authentication methods and associated parameters supported for transport authentication in a policy. The section can list more than one method and only one method must be satisfied for the authentication to pass. However, as of the Istio 0.7 release, the only transport authentication method currently supported is mutual TLS. If you don't need transport authentication, skip this section entirely.

The following example shows the peers: section enabling transport authentication using mutual TLS.

{{< text yaml >}} peers:

• mtls: {} {{< /text >}}

Currently, the mutual TLS setting doesn’t require any parameters. Hence, -mtls: {}, - mtls: or - mtls: null declarations are treated the same. In the future, the mutual TLS setting may carry arguments to provide different mutual TLS implementations.

Origin authentication

The origins: section defines authentication methods and associated parameters supported for origin authentication. Istio only supports JWT origin authentication. However, a policy can list multiple JWTs by different issuers. Similar to peer authentication, only one of the listed methods must be satisfied for the authentication to pass.

The following example policy specifies an origins: section for origin authentication that accepts JWTs issued by Google:

{{< text yaml >}} origins:

• jwt: issuer: "https://accounts.google.com" jwksUri: "https://www.googleapis.com/oauth2/v3/certs" {{< /text >}}

Principal binding

The principal binding key-value pair defines the principal authentication for a policy. By default, Istio uses the authentication configured in the peers: section. If no authentication is configured in the peers: section, Istio leaves the authentication unset. Policy writers can overwrite this behavior with the USE_ORIGIN value. This value configures Istio to use the origin's authentication as the principal authentication instead. In future, we will support conditional binding, for example: USE_PEER when peer is X, otherwise USE_ORIGIN.

The following example shows the principalBinding key with a value of USE_ORIGIN:

{{< text yaml >}} principalBinding: USE_ORIGIN {{< /text >}}

Updating authentication policies

You can change an authentication policy at any time and Istio pushes the change to the endpoints almost in real time. However, Istio can't guarantee that all endpoints receive a new policy at the same time. The following are recommendations to avoid disruption when updating your authentication policies:

• To enable or disable mutual TLS: Use a temporary policy with a mode: key and a PERMISSIVE value. This configures receiving services to accept both types of traffic: plain text and TLS. Thus, no request is dropped. Once all clients switch to the expected protocol, with or without mutual TLS, you can replace the PERMISSIVE policy with the final policy. For more information, visit the Mutual TLS Migration tutorial.

{{< text yaml >}} peers:

• mTLS: mode: PERMISSIVE {{< /text >}}

• For JWT authentication migration: requests should contain new JWT before changing policy. Once the server side has completely switched to the new policy, the old JWT, if there is any, can be removed. Client applications need to be changed for these changes to work.

Authorization

Istio's authorization feature - also known as Role-based Access Control (RBAC)

• provides namespace-level, service-level, and method-level access control for services in an Istio Mesh. It features:

• Role-Based semantics, which are simple and easy to use.

• Service-to-service and end-user-to-service authorization.

• Flexibility through custom properties support, for example conditions, in roles and role-bindings.

• High performance, as Istio authorization is enforced natively on Envoy.

Authorization architecture

{{< image width="90%" ratio="56.25%" link="./authz.svg" alt="Istio Authorization" caption="Istio Authorization Architecture" >}}

The above diagram shows the basic Istio authorization architecture. Operators specify Istio authorization policies using .yaml files. Once deployed, Istio saves the policies in the Istio Config Store.

Pilot watches for changes to Istio authorization policies. It fetches the updated authorization policies if it sees any changes. Pilot distributes Istio authorization policies to the Envoy proxies that are co-located with the service instances.

Each Envoy proxy runs an authorization engine that authorizes requests at runtime. When a request comes to the proxy, the authorization engine evaluates the request context against the current authorization policies, and returns the authorization result, ALLOW or DENY.

Enabling authorization

You enable Istio Authorization using a RbacConfig object. The RbacConfig object is a mesh-wide singleton with a fixed name value of default. You can only use one RbacConfig instance in the mesh. Like other Istio configuration objects, RbacConfig is defined as a Kubernetes CustomResourceDefinition (CRD) object.

In the RbacConfig object, the operator can specify a mode value, which can be:

• OFF: Istio authorization is disabled.
• ON: Istio authorization is enabled for all services in the mesh.
• ON_WITH_INCLUSION: Istio authorization is enabled only for services and namespaces specified in the inclusion field.
• ON_WITH_EXCLUSION: Istio authorization is enabled for all services in the mesh except the services and namespaces specified in the exclusion field.

In the following example, Istio authorization is enabled for the default namespace.

{{< text yaml >}} apiVersion: "config.istio.io/v1alpha2" kind: RbacConfig metadata: name: default namespace: istio-system spec: mode: ON_WITH_INCLUSION inclusion: namespaces: ["default"] {{< /text >}}

Authorization policy

To configure an Istio authorization policy, you specify a ServiceRole and ServiceRoleBinding. Like other Istio configuration objects, they are defined as Kubernetes CustomResourceDefinition (CRD) objects.

• ServiceRole defines a group of permissions to access services.
• ServiceRoleBinding grants a ServiceRole to particular subjects, such as a user, a group, or a service.

The combination of ServiceRole and ServiceRoleBinding specifies: who is allowed to do what under which conditions. Specifically:

• who refers to the subjects: section in ServiceRoleBinding.
• what refers to the permissions: section in ServiceRole.
• which conditions refers to the conditions: section you can specify with the Istio attributes in either ServiceRole or ServiceRoleBinding.

ServiceRole

A ServiceRole specification includes a list of rules:, AKA permissions. Each rule has the following standard fields:

• services: A list of service names. You can set the value to * to include all services in the specified namespace.

• methods: A list of HTTP method names, for permissions on gRPC requests, the HTTP verb is always POST. You can set the value to * to include all HTTP methods.

• paths: HTTP paths or gRPC methods. The gRPC methods must be in the form of /packageName.serviceName/methodName and are case sensitive.

A ServiceRole specification only applies to the namespace specified in the metadata section. The services: and methods: fields are required in a rule. paths: is optional. If a rule is not specified or if it is set to *, it applies to any instance.

The example below shows a simple role: service-admin, which has full access to all services in the default namespace.

{{< text yaml >}} apiVersion: "rbac.istio.io/v1alpha1" kind: ServiceRole metadata: name: service-admin namespace: default spec: rules:

• services: [""] methods: [""] {{< /text >}}

Here is another role: products-viewer, which has read, "GET" and "HEAD", access to the service products.default.svc.cluster.local in the default namespace.

{{< text yaml >}} apiVersion: "rbac.istio.io/v1alpha1" kind: ServiceRole metadata: name: products-viewer namespace: default spec: rules:

• services: ["products.default.svc.cluster.local"] methods: ["GET", "HEAD"] {{< /text >}}

In addition, we support prefix matching and suffix matching for all the fields in a rule. For example, you can define a tester role with the following permissions in the default namespace:

• Full access to all services with prefix "test-*", for example: test-bookstore, test-performance, test-api.default.svc.cluster.local.
• Read ("GET") access to all paths with "*/reviews" suffix, for example: /books/reviews, /events/booksale/reviews, /reviews in service bookstore.default.svc.cluster.local.

{{< text yaml >}} apiVersion: "rbac.istio.io/v1alpha1" kind: ServiceRole metadata: name: tester namespace: default spec: rules:

• services: ["test-"] methods: [""]
• services: ["bookstore.default.svc.cluster.local"] paths: ["*/reviews"] methods: ["GET"] {{< /text >}}

In a ServiceRole, the combination of namespace: + services: + paths: + methods: defines how a service or services are accessed. In some situations, you may need to specify additional conditions for your rules. For example, a rule may only apply to a certain version of a service, or only apply to services with a specific label, like "foo". You can easily specify these conditions using constraints:.

For example, the following ServiceRole definition adds a constraint that request.headers["version"] is either "v1" or "v2" extending the previous products-viewer role. The supported key: values of a constraint are listed in the constraints and properties page. In the case that the attribute is a map, for example request.headers, the key is an entry in the map, for example request.headers["version"].

{{< text yaml >}} apiVersion: "rbac.istio.io/v1alpha1" kind: ServiceRole metadata: name: products-viewer-version namespace: default spec: rules:

• services: ["products.default.svc.cluster.local"] methods: ["GET", "HEAD"] constraints:
  • key: request.headers[version] values: ["v1", "v2"] {{< /text >}}

ServiceRoleBinding

A ServiceRoleBinding specification includes two parts:

• roleRef refers to a ServiceRole resource in the same namespace.
• A list of subjects: that are assigned to the role.

You can either explicitly specify a subject with a user: or with a set of properties:. A property in a ServiceRoleBinding subject is similar to a constraint in a ServiceRole specification. A property also lets you use conditions to specify a set of accounts assigned to this role. It contains a key: and its allowed values. The supported key: values of a constraint are listed in the constraints and properties page.

The following example shows a ServiceRoleBinding named test-binding-products, which binds two subjects to the ServiceRole named "product-viewer" and has the following subjects:

• A service account representing service a, "service-account-a".
• A service account representing the Ingress service "istio-ingress-service-account" and where the JWT "email" claim is "a@foo.com".

{{< text yaml >}} apiVersion: "rbac.istio.io/v1alpha1" kind: ServiceRoleBinding metadata: name: test-binding-products namespace: default spec: subjects:

• user: "service-account-a"
• user: "istio-ingress-service-account" properties: request.auth.claims[email]: "a@foo.com" roleRef: kind: ServiceRole name: "products-viewer" {{< /text >}}

In case you want to make a services publicly accessible, you can set the subject to user: "*". This value assigns the ServiceRole to all users and services, for example:

{{< text yaml >}} apiVersion: "rbac.istio.io/v1alpha1" kind: ServiceRoleBinding metadata: name: binding-products-allusers namespace: default spec: subjects:

• user: "*" roleRef: kind: ServiceRole name: "products-viewer" {{< /text >}}