OpenShift - Run a deployment with a Service Account and Security Context Constraint

If you are not familiar with the oc command, refer to OpenShift - Getting Started with the oc command.

Role Bindings and Security Context Constraint are similar in that they both are access control mechanisms.

  • Role Bindings are used to control what an OpenShift Users are allowed to do
  • Security Context Constraints are used to control what pods are allowed to do

A Security Context Constraint is used to control certain things that a deployment or pod is allowed or not allowed to do, such as mounting a host volume. Typically, a Security Context Constraint (SCC) is associated with a Service Account.

Let's say you have created a Service Account named my-service-account.

~]$ oc create serviceaccount my-service-account
serviceaccount/my-service-account created

 

The oc get serviceaccounts (or just oc get sa) command can be used to list the Service Accounts that have been created in the current project / namespace.

~]$ oc get serviceaccounts
NAME                  SECRETS   AGE
default               2         388d
my-servie-account     2         112s

 

The oc describe serviceaccount command can be used to show more details of a specific Service Account.

~]$ oc describe serviceaccount my-service-account
Name:                my-service-account
Namespace:           my-project
Labels:              <none>
Annotations:         <none>
Image pull secrets:  my-service-account-dockercfg-57b6r
Mountable secrets:   my-service-account-token-sfrpr
                     my-service-account-dockercfg-57b6r
Tokens:              my-service-account-token-6x45k
                     my-service-account-token-sfrpr
Events:              <none>

 

Before you update a container in a deployment with the Service Account, you want to associate the Service Account with a Security Context Contraint (SCC)

~]$ oc adm policy add-scc-to-user restricted -z my-service-account
clusterrole.rbac.authorization.k8s.io/system:openshift:scc:restricted added: "my-service-account"

 

Then the oc set serviceaccount command can be used to have a deployment / pod run by the Service Account which will apply the Security Context Contraint (SCC) to the container / deployment / pod.

~]$ oc set serviceaccount deployment my-deployment my-service-account
deployment.apps/my-deployment serviceaccount updated

 

Or, you could use the oc edit or oc patch command to update the deployment YAML file.

~]$ oc patch deployment my-deployment --patch '{"spec":{"template":{"spec":{"serviceAccount":"my-service-account","serviceAccountName":"my-service-account"}}}}'

 

This command will update the deployment YAML to have the serviceAccount and serviceAccountName keys. 

spec:
  template:
    spec:
      serviceAccount: my-service-account
      serviceAccountName: my-service-account

 

And then this one liner can be used to see that the deployment has the Service Account and the restricted Security Context Contraint (SCC).

~]# oc get deployment my-app --output yaml | oc adm policy scc-review --filename - 
RESOURCE                    SERVICE ACCOUNT       ALLOWED BY         
Deployment/my-deployment    my-service-account    restricted

 

The oc get pods command can be used to see that a new pod should be created.

~]$ oc get pods
NAME                  READY   STATUS      RESTARTS   AGE
my-deployment-mkfjk   1/1     Running     0          4m46s

 

The oc describe pod command should show that the pod has the restricted Security Context Contraint.

~]$ oc describe pod my-deployment-mkfjk
Name:         my-deployment-mkfjk
Namespace:    my-project
Annotations:  openshift.io/scc: restricted

 




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