Kubernetes Auth Method

The kubernetes auth method type allows for a Kubernetes service account token to be used to authenticate to Consul. This method of authentication makes it easy to introduce a Consul token into a Kubernetes pod.

This page assumes general knowledge of Kubernetes and the concepts described in the main auth method documentation.

Config Parameters

The following auth method Config parameters are required to properly configure an auth method of type kubernetes:

• Host (string: <required>) - Must be a host string, a host:port pair, or a URL to the base of the Kubernetes API server.

• CACert (string: <required>) - PEM encoded CA cert for use by the TLS client used to talk with the Kubernetes API. NOTE: Every line must end with a newline (\n). If not set, system certificates are used.

• ServiceAccountJWT (string: <required>) - A Service Account Token (JWT) used by the Consul leader to validate application JWTs during login.

• MapNamespaces (bool: <false>) EnterpriseEnterprise - Deprecated in Consul 1.8.0 in favor of namespace rules. Indicates whether the auth method should attempt to map the Kubernetes namespace to a Consul namespace instead of creating tokens in the auth methods own namespace. Note that mapping namespaces requires the auth method to reside within the default namespace. Deprecated in Consul 1.8.0 in favor of namespace rules.

• ConsulNamespacePrefix (string: <optional>) EnterpriseEnterprise - Deprecated in Consul 1.8.0 in favor of namespace rules. When MapNamespaces is enabled, this value will be prefixed to the Kubernetes namespace to determine the Consul namespace to create the new token within. Deprecated in Consul 1.8.0 in favor of namespace rules.

• ConsulNamespaceOverrides (map: <string:string>) EnterpriseEnterprise - Deprecated in Consul 1.8.0 in favor of namespace rules. This field is a mapping of Kubernetes namespace names to Consul namespace names. If a Kubernetes namespace is present within this map, the value will be used without adding the ConsulNamespacePrefix. If the value in the map is "" then the auth methods namespace will be used instead of attempting to determine an alternate namespace. Deprecated in Consul 1.8.0 in favor of namespace rules.

Sample Config

{
    ...other fields...
    "Config": {
        "Host": "https://192.0.2.42:8443",
        "CACert": "-----BEGIN CERTIFICATE-----\n...-----END CERTIFICATE-----\n",
        "ServiceAccountJWT": "eyJhbGciOiJSUzI1NiIsImtpZCI6IiJ9..."
    }
}

RBAC

The Kubernetes service account corresponding to the configured ServiceAccountJWT needs to have access to two Kubernetes APIs:

• TokenReview

  Kubernetes should be running with --service-account-lookup. This is defaulted to true in Kubernetes 1.7, but any versions prior should ensure the Kubernetes API server is started with this setting.

• ServiceAccount

The following is an example RBAC configuration snippet to grant the necessary permissions to a service account named consul-auth-method-example:

---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: review-tokens
  namespace: default
subjects:
  - kind: ServiceAccount
    name: consul-auth-method-example
    namespace: default
roleRef:
  kind: ClusterRole
  name: system:auth-delegator
  apiGroup: rbac.authorization.k8s.io
---
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: service-account-getter
  namespace: default
rules:
  - apiGroups: ['']
    resources: ['serviceaccounts']
    verbs: ['get']
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: get-service-accounts
  namespace: default
subjects:
  - kind: ServiceAccount
    name: consul-auth-method-example
    namespace: default
roleRef:
  kind: ClusterRole
  name: service-account-getter
  apiGroup: rbac.authorization.k8s.io

Kubernetes Authentication Details

Initially the ServiceAccountJWT given to the Consul leader uses the TokenReview API to validate the provided JWT. The trusted attributes of serviceaccount.namespace, serviceaccount.name, and serviceaccount.uid are populated directly from the Service Account metadata.

The Consul leader makes an additional query, this time to the ServiceAccount API to check for the existence of an annotation of consul.hashicorp.com/service-name on the ServiceAccount object. If one is found its value will override the trusted attribute of serviceaccount.name for the purposes of evaluating any binding rules.

Trusted Identity Attributes

The authentication step returns the following trusted identity attributes for use in binding rule selectors and bind name interpolation.