Overview

When a person uses the OpenShift Container Platform 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

Every service account is also a member of two groups:

system:serviceaccount

Includes all service accounts in the system.

system:serviceaccount:<project>

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:serviceaccount -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:serviceaccount: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 Docker 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.

Enabling Service Account Authentication

Service accounts authenticate to the API using tokens signed by a private RSA key. The authentication layer verifies the signature using a matching public RSA key.

To enable service account token generation, update the serviceAccountConfig stanza in the /etc/origin/master/master-config.yml file on the master to specify a privateKeyFile (for signing), and a matching public key file in the publicKeyFiles list:

serviceAccountConfig:
  ...
  masterCA: ca.crt (1)
  privateKeyFile: serviceaccount.private.key (2)
  publicKeyFiles:
  - serviceaccount.public.key (3)
  - ...
1 CA file used to validate the API server’s serving certificate.
2 Private RSA key file (for token signing).
3 Public RSA key files (for token verification). If private key files are provided, then the public key component is used. Multiple public key files can be specified, and a token will be accepted if it can be validated by one of the public keys. This allows rotation of the signing key, while still accepting tokens generated by the previous signer.

Managed Service Accounts

Service accounts are required in each project to run builds, deployments, and other pods. The managedNames setting in the /etc/origin/master/master-config.yml file on the master controls which service accounts are automatically created in every project:

serviceAccountConfig:
  ...
  managedNames: (1)
  - builder (2)
  - deployer (3)
  - default (4)
  - ...
1 List of service accounts to automatically create in every project.
2 A builder service account in each project is required by build pods, and is given the system:image-builder role, which allows pushing images to any image stream in the project using the internal container registry.
3 A deployer service account in each project is required by deployment pods, and is given the system:deployer role, which allows viewing and modifying replication controllers and pods in the project.
4 A default service account is used by 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 registry.

Infrastructure Service Accounts

Several infrastructure controllers run using service account credentials. The following service accounts are created in the OpenShift Container Platform infrastructure project (openshift-infra) at server start, and given the following roles cluster-wide:

Service Account Description

replication-controller

Assigned the system:replication-controller role

deployment-controller

Assigned the system:deployment-controller role

build-controller

Assigned the system:build-controller role. Additionally, the build-controller service account is included in the privileged security context constraint in order to create privileged build pods.

To configure the project where those service accounts are created, set the openshiftInfrastructureNamespace field in the /etc/origin/master/master-config.yml file on the master:

policyConfig:
  ...
  openshiftInfrastructureNamespace: openshift-infra

Service Accounts and Secrets

Set the limitSecretReferences field in the /etc/origin/master/master-config.yml file on the master to true to require pod secret references to be whitelisted by their service accounts. Set its value to false to allow pods to reference any secret in the project.

serviceAccountConfig:
  ...
  limitSecretReferences: false

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 secrets new secret-plans plan1.txt plan2.txt
secret/secret-plans

$ oc secrets new-dockercfg 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: "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 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