[Feature flag] gitaly_disable_spawn_token_queue

What

Enable gitaly_disable_spawn_token_queue feature flag.

Related #5901 (closed)

Owners

• Team: Gitaly
• Most appropriate slack channel to reach out to: #g_gitaly
• Best individual to reach out to: @samihiltunen

Expectations

What release does this feature occur in first?

17.5

What are we expecting to happen?

Gitaly stops using the spawn token mechanism. With that, Gitaly no longer limits the concurrency of process spawning.

What might happen if this goes wrong?

We see increased load that degrades service quality.

What can we monitor to detect problems with this?

Gitaly Apdex: https://dashboards.gitlab.net/d/gitaly-main/gitaly3a-overview?orgId=1

Roll Out Steps

• Enable on staging
  • Is the required code deployed on staging? (howto)
  • Enable on staging (howto)
  • Add featureflagstaging to this issue (howto)
  • Test on staging (howto)
  • Verify the feature flag was used by checking Prometheus metric gitaly_feature_flag_checks_total
• Enable on production
  • Is the required code deployed on production? (howto)
  • Progressively enable in production (howto)
  • Add featureflagproduction to this issue
  • Verify the feature flag was used by checking Prometheus metric gitaly_feature_flag_checks_total
• Create subsequent issues
  • To default enable the feature flag (optional, only required if backwards-compatibility concerns exist)
    • Create issue using the Feature Flag Default Enable template.
    • Set milestone to current+1 release
  • To Remove feature flag
    • Create issue using the Feature Flag Removal template.
    • Set milestone to current+1 (+2 if we created an issue to default enable the flag).

Please refer to the documentation of feature flags for further information.