Ansible variable for keys check

Background:

I have a working cluster with 3 masters and 5 nodes. I ask my colleague to add another node into the cluster. He clones KTRW and our repository that contains our inventory file. He adds the new node into the inventory file.

If he runs the Ansible playbook now, it will destroy the cluster, since he has no keys on his machine.

I was thinking that we could have a validation parameter. If the parameter is set to `true`, it could check if vital keys are missing (for example the `service-account-key.pem`) and if so, simply fail the playbook, explaining that the user needs the keys to continue.

What do you think? Just as a safety measure.