MySQL Open Files Limit.
Verify the open-files-limit configuration is high enough https://access.redhat.com/solutions/1598733
Verify all deployed nodes have their clock synchronised..
Each overcloud node should have their clocks synchronised. The deployment should configure and run ntpd. This validation verifies that it is indeed running and connected to an NPT server on all nodes.
Check the status of the pacemaker cluster.
This runs pcs status and checks for any failed actions. A failed status post-deployment indicates something is not configured correctly. This should also be run before upgrade as the process will likely fail with a cluster that’s not completely healthy.
Rabbitmq limits.
Make sure the rabbitmq file descriptor limits are set to reasonable values.
Verify token_flush is enabled in keystone users crontab..
Without a token_flush crontab enabled for the keystone user, the keystone database can grow very large. This validation checks that the keystone token_flush crontab has been set up.