Service Accounts

A service account provides an identity for processes that run in a Pod.

This is a user introduction to Service Accounts. See also the Cluster Admin Guide to Service Accounts.

Note: This document describes how service accounts behave in a cluster set up as recommended by the Kubernetes project. Your cluster administrator may have customized the behavior in your cluster, in which case this documentation may not apply.

When you (a human) access the cluster (e.g. using kubectl), you are authenticated by the apiserver as a particular User Account (currently this is usually admin, unless your cluster administrator has customized your cluster). Processes in containers inside pods can also contact the apiserver. When they do, they are authenticated as a particular Service Account (e.g. default).

Using the Default Service Account to access the API server.

When you create a pod, you do not need to specify a service account. It is automatically assigned the default service account of the same namespace. If you get the raw json or yaml for a pod you have created (e.g. kubectl get pods/podname -o yaml), you can see the spec.serviceAccount field has been automatically set.

You can access the API using a proxy or with a client library, as described in Accessing the Cluster.

Using Multiple Service Accounts.

Every namespace has a default service account resource called default. You can list this and any other serviceAccount resources in the namespace with this command:

$ kubectl get serviceAccounts
NAME      SECRETS
default   1

You can create additional serviceAccounts like this:

$ cat > /tmp/serviceaccount.yaml <<EOF
apiVersion: v1
kind: ServiceAccount
metadata:
  name: build-robot
EOF
$ kubectl create -f /tmp/serviceaccount.yaml
serviceaccounts/build-robot

If you get a complete dump of the service account object, like this:

$ kubectl get serviceaccounts/build-robot -o yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  creationTimestamp: 2015-06-16T00:12:59Z
  name: build-robot
  namespace: default
  resourceVersion: "272500"
  selfLink: /api/v1/namespaces/default/serviceaccounts/build-robot
  uid: 721ab723-13bc-11e5-aec2-42010af0021e
secrets:
- name: build-robot-token-bvbk5

then you will see that a token has automatically been created and is referenced by the service account.

You may use the ABAC authorization plugin to set permissions on service accounts.

To use a non-default service account, simply set the spec.serviceAccount field of a pod to the name of the service account you wish to use.

The service account has to exist at the time the pod is created, or it will be rejected.

You cannot update the service account of an already created pod.

You can clean up the service account from this example like this:

$ kubectl delete serviceaccount/build-robot

Note that if a pod does not have a ServiceAccount set, the ServiceAccount will be set to default.

Manually create a service account API token.

Suppose we have an existing service account named “build-robot” as mentioned above, and we create a new secret manually.

$ cat > /tmp/build-robot-secret.yaml <<EOF
apiVersion: v1
kind: Secret
metadata:
  name: build-robot-secret
  annotations: 
    kubernetes.io/service-account.name: build-robot
type: kubernetes.io/service-account-token
EOF
$ kubectl create -f /tmp/build-robot-secret.yaml
secrets/build-robot-secret

Now you can confirm that the newly built secret is populated with an API token for the “build-robot” service account.

Any tokens for non-existent service accounts will be cleaned up by the token controller.

$ kubectl describe secrets/build-robot-secret 
Name:   build-robot-secret
Namespace:  default
Labels:   <none>
Annotations:  kubernetes.io/service-account.name=build-robot,kubernetes.io/service-account.uid=870ef2a5-35cf-11e5-8d06-005056b45392

Type: kubernetes.io/service-account-token

Data
====
ca.crt: 1220 bytes
token: ...
namespace: 7 bytes

Note that the content of token is elided here.

Adding ImagePullSecrets to a service account

First, create an imagePullSecret, as described here Next, verify it has been created. For example:

$ kubectl get secrets myregistrykey
NAME             TYPE                              DATA
myregistrykey    kubernetes.io/.dockerconfigjson   1

Next, read/modify/write the service account for the namespace to use this secret as an imagePullSecret

$ kubectl get serviceaccounts default -o yaml > ./sa.yaml
$ cat sa.yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  creationTimestamp: 2015-08-07T22:02:39Z
  name: default
  namespace: default
  resourceVersion: "243024"
  selfLink: /api/v1/namespaces/default/serviceaccounts/default
  uid: 052fb0f4-3d50-11e5-b066-42010af0d7b6
secrets:
- name: default-token-uudge
$ vi sa.yaml
[editor session not shown]
[delete line with key "resourceVersion"]
[add lines with "imagePullSecret:"]
$ cat sa.yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  creationTimestamp: 2015-08-07T22:02:39Z
  name: default
  namespace: default
  selfLink: /api/v1/namespaces/default/serviceaccounts/default
  uid: 052fb0f4-3d50-11e5-b066-42010af0d7b6
secrets:
- name: default-token-uudge
imagePullSecrets:
- name: myregistrykey
$ kubectl replace serviceaccount default -f ./sa.yaml
serviceaccounts/default

Now, any new pods created in the current namespace will have this added to their spec:

spec:
  imagePullSecrets:
  - name: myregistrykey

Adding Secrets to a service account.

TODO: Test and explain how to use additional non-K8s secrets with an existing service account.

TODO explain:

The token goes to: “/var/run/secrets/kubernetes.io/serviceaccount/$WHATFILENAME”