Is it mandatory to use Cribl UI to upgrade the Leader and nodes?

Or can I can use my playbooks in Ansible etc? Please advise

You are free to upgrade your Cribl instances the way you prefer. There are many ways:

  1. Manually
  2. Via the Cribl UI
  3. Using Ansible/Salt/Puppet/etc. playbooks
  4. Updating the Helm Chart or image tag when deploying on Kubernetes

For more information, consult the docs: Upgrading | Cribl Docs