Service Accounts

Service Accounts

Overview

When a person uses the OKD CLI or web console, their API token authenticates them to the OpenShift API. However, when a regular user’s credentials are not available, it is common for components to make API calls independently. For example:

Replication controllers make API calls to create or delete pods.
Applications inside containers could make API calls for discovery purposes.
External applications could make API calls for monitoring or integration purposes.

Service accounts provide a flexible way to control API access without sharing a regular user’s credentials.

User Names and Groups

Every service account has an associated user name that can be granted roles, just like a regular user. The user name is derived from its project and name:

system:serviceaccount:<project>:<name>

For example, to add the view role to the robot service account in the top-secret project:

$ oc policy add-role-to-user view system:serviceaccount:top-secret:robot

If you want to grant access to a specific service account in a project, you can use the -z flag. From the project to which the service account belongs, use the -z flag and specify the <serviceaccount_name>. This is highly recommended, as it helps prevent typos and ensures that access is granted only to the specified service account. For example:

 $ oc policy add-role-to-user <role_name> -z <serviceaccount_name>

If not in the project, use the -n option to indicate the project namespace it applies to, as shown in the examples below.

Every service account is also a member of two groups:

system:serviceaccounts

Includes all service accounts in the system.

system:serviceaccounts:

Includes all service accounts in the specified project.

For example, to allow all service accounts in all projects to view resources in the top-secret project:

$ oc policy add-role-to-group view system:serviceaccounts -n top-secret

To allow all service accounts in the managers project to edit resources in the top-secret project:

$ oc policy add-role-to-group edit system:serviceaccounts:managers -n top-secret

Default Service Accounts and Roles

Three service accounts are automatically created in every project:

Service Account	Usage
builder	Used by build pods. It is given the system:image-builder role, which allows pushing images to any image stream in the project using the internal Docker registry.
deployer	Used by deployment pods and is given the system:deployer role, which allows viewing and modifying replication controllers and pods in the project.
default	Used to run all other pods unless they specify a different service account.

All service accounts in a project are given the system:image-puller role, which allows pulling images from any image stream in the project using the internal container image registry.

Managing Service Accounts

Service accounts are API objects that exist within each project. To manage service accounts, you can use the oc command with the sa or serviceaccount object type or use the web console.

To get a list of existing service accounts in the current project:

$ oc get sa
NAME       SECRETS   AGE
builder    2         2d
default    2         2d
deployer   2         2d

To create a new service account:

$ oc create sa robot
serviceaccount "robot" created

As soon as a service account is created, two secrets are automatically added to it:

an API token
credentials for the OpenShift Container Registry

These can be seen by describing the service account:

$ oc describe sa robot
Name:        robot
Namespace:    project1
Labels:        <none>
Annotations:    <none>
Image pull secrets:    robot-dockercfg-qzbhb
Mountable secrets:     robot-token-f4khf
                       robot-dockercfg-qzbhb
Tokens:                robot-token-f4khf
                       robot-token-z8h44

The system ensures that service accounts always have an API token and registry credentials.

The generated API token and registry credentials do not expire, but they can be revoked by deleting the secret. When the secret is deleted, a new one is automatically generated to take its place.

Managing Allowed Secrets

In addition to providing API credentials, a pod’s service account determines which secrets the pod is allowed to use.

Pods use secrets in two ways:

image pull secrets, providing credentials used to pull images for the pod’s containers
mountable secrets, injecting the contents of secrets into containers as files

To allow a secret to be used as an image pull secret by a service account’s pods, run:

$ oc secrets link --for=pull <serviceaccount-name> <secret-name>

To allow a secret to be mounted by a service account’s pods, run:

$ oc secrets link --for=mount <serviceaccount-name> <secret-name>

Limiting secrets to only the service accounts that reference them is disabled by default. This means that if serviceAccountConfig.limitSecretReferences is set to false (the default setting) in the master configuration file, mounting secrets to a service account’s pods with the —for=mount option is not required. However, using the —for=pull option to enable using an image pull secret is required, regardless of the serviceAccountConfig.limitSecretReferences value.

This example creates and adds secrets to a service account:

$ oc create secret generic secret-plans \
    --from-file=plan1.txt \
    --from-file=plan2.txt
secret/secret-plans
$ oc create secret docker-registry my-pull-secret \
    --docker-username=mastermind \
    --docker-password=12345 \
    --docker-email=mastermind@example.com
secret/my-pull-secret
$ oc secrets link robot secret-plans --for=mount
$ oc secrets link robot my-pull-secret --for=pull
$ oc describe serviceaccount robot
Name:               robot
Labels:             <none>
Image pull secrets:    robot-dockercfg-624cx
                       my-pull-secret
Mountable secrets:     robot-token-uzkbh
                       robot-dockercfg-624cx
                       secret-plans
Tokens:                robot-token-8bhpp
                       robot-token-uzkbh

Using a Service Account’s Credentials Inside a Container

When a pod is created, it specifies a service account (or uses the default service account), and is allowed to use that service account’s API credentials and referenced secrets.

A file containing an API token for a pod’s service account is automatically mounted at /var/run/secrets/kubernetes.io/serviceaccount/token.

That token can be used to make API calls as the pod’s service account. This example calls the users/~ API to get information about the user identified by the token:

$ TOKEN="$(cat /var/run/secrets/kubernetes.io/serviceaccount/token)"
$ curl --cacert /var/run/secrets/kubernetes.io/serviceaccount/ca.crt \
    "https://openshift.default.svc.cluster.local/oapi/v1/users/~" \
    -H "Authorization: Bearer $TOKEN"
kind: "User"
apiVersion: "user.openshift.io/v1"
metadata:
  name: "system:serviceaccount:top-secret:robot"
  selflink: "/oapi/v1/users/system:serviceaccount:top-secret:robot"
  creationTimestamp: null
identities: null
groups:
  - "system:serviceaccount"
  - "system:serviceaccount:top-secret"

Using a Service Account’s Credentials Externally

The same token can be distributed to external applications that need to authenticate to the API.

Use the following syntax to view a service account’s API token:

$ oc describe secret <secret-name>

For example:

$ oc describe secret robot-token-uzkbh -n top-secret
Name:        robot-token-uzkbh
Labels:        <none>
Annotations:    kubernetes.io/service-account.name=robot,kubernetes.io/service-account.uid=49f19e2e-16c6-11e5-afdc-3c970e4b7ffe
Type:    kubernetes.io/service-account-token
Data
token:    eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9...
$ oc login --token=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9...
Logged into "https://server:8443" as "system:serviceaccount:top-secret:robot" using the token provided.
You don't have any projects. You can try to create a new project, by running
    $ oc new-project <projectname>
$ oc whoami
system:serviceaccount:top-secret:robot