PowerProtect Data Manager: Kubernetes backup error 'controller pod is not running'

Kubernetes backups start to fail after recovery of PowerProtect Data Manager from its server disaster recovery (This could also apply to other situations):

ABK0002: Unable to back up namespace 'test' in Kubernetes cluster 'my-k8-cluster'.
Review the error details and summary log in the Jobs window or review the log files at /var/log/brs/cndm and /var/log/brs/cndn/k8s for more detailed information to troubleshoot the issue.
Backup failed: controller pod is not running

The following error can be observed in logs:

2021-07-21T03:49:48.340Z ERROR [] [task-5011a057-340f-40fb-8cd8-12414685d058] [][][][TRACE_ID:a66ce529604914ad;JOB_ID:a9b8915af1637407][] [K8sHelperApi.isDone(90)] - Failed to wait on job com.emc.dpsg.ecdm.baseresourceservice.exception.ValidationServiceException: controller pod is not running
2021-07-21T03:50:14.065Z WARN [] [dsSource-plpd-testcluster] [][][][][] [c.e.b.c.s.p.K8sHealthMonitor.checkPodHealth(200)] - Controller Pod is down, cluster: <k8s_cluster_name>, age=PT153H49M43.065S

The 'kubectl describe pod -n PowerProtect' command output shows:

powerprotect     powerprotect-controller-666ffccbbf-p5rwh                   0/1     ImagePullBackOff   0          6d12h
velero-ppdm      backup-driver-587cfcdf59-2mc8p                             1/1     Running            0          49d
velero-ppdm      velero-5df5fcd896-p68rw                                    1/1     Running            0          49d

The pod is unable to pull required images from the configured repositories.

• Validate the Kubernetes cluster can access the required repositories to pull images:
  • Docker Hub: https://hub.docker.com/ (External Link)
  • Quay: https://quay.io/ (External Link) 
• If the repositories are not accessible, pull the images to the Kubernetes cluster local registry. 
• On the PowerProtect Data Manager appliance, create the cndm application properties file:

vi /usr/local/brs/lib/cndm/config/application.properties

• Populate the cndm application properties file with the following:

k8s.docker.registry=fqdn:port For example, k8s.docker.registry=artifacts.example.com:8446
k8s.image.pullsecrets=secret resource name Specify this entry only if you require an image pull secret.

• Restart the cndm daemon: cndm restart
• Run a Kubernetes cluster discovery from the PowerProtect Data Manager Interface.