[Feature flag] Cleanup geo_proxy_direct_to_primary

Summary

This issue is to cleanup the geo_proxy_direct_to_primary feature flag, after the feature flag has been enabled by default for an appropriate amount of time in production.

Owners

• Team: groupgeo
• Most appropriate slack channel to reach out to: #g_geo
• Best individual to reach out to: @mkozono
• PM: @sranasinghe

Stakeholders

• @igor.drozdov

Expectations

What might happen if this goes wrong?

By the time this issue is in play, the FF is already enabled by default. If we break something while removing the dead legacy code, then I believe we'd have to rollback all MRs that were part of the removal.

The most likely problem would be that Git push over SSH against a secondary Geo site would have errors like:

remote: objects:  66% (2/3), 349.95 MiB | 773.00 KiB/s 
remote: ========================================================================
remote: 
remote: ERROR: Remote repository is unavailable

remote: 
remote: ========================================================================
remote: 
send-pack: unexpected disconnect while reading sideband packet
Connection to geo.staging-ref.gitlab.com closed by remote host.
fatal: the remote end hung up unexpectedly

Or ERROR: Internal API unreachable.

Cleaning up the feature flag

• Create a merge request to remove <feature-flag-name> feature flag. Ask for review and merge it.
  • Remove all references to the feature flag from the codebase.
  • Remove the YAML definitions for the feature from the repository.
  • Remove unused Git Proxy endpoints
    • Geo: Perform Git over HTTP requests as a custom... (gitlab-shell#614 - closed)
    • Geo: Send authorization headers to Gitlab Shell... (#390101 - closed)
    • Geo: Move HTTP to SSH conversion from Rails to ... (gitlab-shell#613 - closed)
  • Create a changelog entry.
• Ensure that the cleanup MR has been deployed to both production and canary. If the merge request was deployed before the code cutoff, the feature can be officially announced in a release blog post.
  • /chatops run auto_deploy status <merge-commit-of-cleanup-mr>
• Close the feature issue to indicate the feature will be released in the current milestone.
• If not already done, clean up the feature flag from all environments by running these chatops command in #production channel:
  • /chatops run feature delete <feature-flag-name> --dev
  • /chatops run feature delete <feature-flag-name> --staging
  • /chatops run feature delete <feature-flag-name>
• Close this rollout issue.