Mention deleting gitlab-cluster.json

What does this MR do?

Slack conversation (internal):

Customer asking about these kindss of messages (seeing it for the secondary too) after a bit of a messy recovery (afaik everything is up an running now).

The 'geo_primary_role' is defined in /etc/gitlab/gitlab-cluster.json as 'true' and overrides the setting in the /etc/gitlab/gitlab.rb

I'm not finding any specific documentation / issues or other slack messages on this. Can it be ignored? Any specific actions/steps that need to be taken?

The customer in this case tried to promote a secondary, realized the secondary wasn't up to date and is looking to get it added back as a secondary, and is seeing those warnings during a reconfigure.

I feel like just initiating the replication process would update/replace and make these warnings go away. But maybe they need to explicitly update or delete the gitlab-cluster.json

I suspect you are correct, that you may need to delete gitlab-cluster.json when adding a former primary site readding a former secondary site as a secondary. If so, we probably need to mention this to https://docs.gitlab.com/ee/administration/geo/disaster_recovery/bring_primary_back.html

IIUC, the main purpose of gitlab-cluster.json is to allow the gitlab-ctl geo promote command to override gitlab.rb settings since gitlab.rb is user-configured and should not be modified by GitLab code, but gitlab.rb may contain secondary-specific settings which don't make sense after promotion.

If gitlab-cluster.json only contains overrides like "actually this is a primary" or "disable these secondary-specific services", then I think it can be safely deleted when demoting.

Yes, you can delete the gitLab-cluster.json file.

Every Sidekiq, PostgreSQL, Gitaly, and Rails nodes has this file.

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