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[Feature flag] Rollout of `track_gitlab_schema_in_current_transaction`

Summary

This issue is to rollout the feature on production, that is currently behind the track_gitlab_schema_in_current_transaction feature flag.

Owners

  • Team: Sharding group
  • Most appropriate slack channel to reach out to: #g_sharding
  • Best individual to reach out to: Thong Kuah @tkuah
  • PM: @fzimmer

Stakeholders

Expectations

What are we expecting to happen?

  1. Transactions perform as usual (no performance impact)
  2. We might see some cross-database modification errors in Sentry arising from transactions operating in the wrong database (#347368 (closed))

When is the feature viable?

What might happen if this goes wrong?

  • We could see dips in Apdex because the performance related to transaction dips

We can disable this feature flag at any time. There is no impact to disabling the feature flag as the flag exists solely to raise errors with Sentry

What can we monitor to detect problems with this?

Consider mentioning checks for 5xx errors or other anomalies like an increase in redirects (302 HTTP response status)

Drops in Apdex

Drops in transaction

What can we check for monitoring production after rollouts?

Consider adding links to check for Sentry errors, Production logs for 5xx, 302s, etc.

Rollout Steps

Rollout on non-production environments

  • Ensure that the feature MRs have been deployed to non-production environments.
    • /chatops run auto_deploy status <merge-commit-of-your-feature>
  • /chatops run feature set track_gitlab_schema_in_current_transaction 50 --staging
  • Enable the feature globally on non-production environments.
    • /chatops run feature set track_gitlab_schema_in_current_transaction true --dev
    • /chatops run feature set track_gitlab_schema_in_current_transaction true --staging
  • Verify that the feature works as expected. Posting the QA result in this issue is preferable.

Preparation before global rollout

  • Check if the feature flag change needs to be accompanied with a change management issue. Cross link the issue here if it does.
  • Ensure that you or a representative in development can be available for at least 2 hours after feature flag updates in production. If a different developer will be covering, or an exception is needed, please inform the oncall SRE by using the @sre-oncall Slack alias.
  • Ensure that documentation has been updated (More info).
  • Announce on the feature issue an estimated time this will be enabled on GitLab.com.
  • Notify #support_gitlab-com and your team channel (more guidance when this is necessary in the dev docs).

Global rollout on production

For visibility, all /chatops commands that target production should be executed in the #production slack channel and cross-posted (with the command results) to the responsible team's slack channel (#g_TEAM_NAME).

  • Incrementally roll out the feature.
    • If the feature flag in code does NOT have an actor, perform time-based rollout (random rollout).
      • /chatops run feature set track_gitlab_schema_in_current_transaction 10
      • /chatops run feature set track_gitlab_schema_in_current_transaction 25
      • /chatops run feature set track_gitlab_schema_in_current_transaction 50
      • /chatops run feature set track_gitlab_schema_in_current_transaction 75
      • /chatops run feature set track_gitlab_schema_in_current_transaction 100
    • Enable the feature globally on production environment.
      • /chatops run feature set track_gitlab_schema_in_current_transaction true
  • Announce on the feature issue that the feature has been globally enabled.
  • Wait for at least one day for the verification term.

(Optional) Release the feature with the feature flag

If you're still unsure whether the feature is deemed stable but want to release it in the current milestone, you can change the default state of the feature flag to be enabled. To do so, follow these steps:

  • Create a merge request with the following changes. Ask for review and merge it.
  • Ensure that the default-enabling 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-default-enabling-mr>
  • Close the feature issue to indicate the feature will be released in the current milestone.
  • Set the next milestone to this rollout issue for scheduling the flag removal.
  • (Optional) You can create a separate issue for scheduling the steps below to Release the feature.
    • Set the title to "[Feature flag] Cleanup <feature-flag-name>".
    • Execute the /copy_metadata <this-rollout-issue-link> quick action to copy the labels from this rollout issue.
    • Link this rollout issue as a related issue.
    • Close this rollout issue.

WARNING: This approach has the downside that it makes it difficult for us to clean up the flag. For example, on-premise users could disable the feature on their GitLab instance. But when you remove the flag at some point, they suddenly see the feature as enabled and they can't roll it back to the previous behavior. To avoid this potential breaking change, use this approach only for urgent matters.

Release the feature

After the feature has been deemed stable, the clean up should be done as soon as possible to permanently enable the feature and reduce complexity in the codebase.

  • 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.
    • 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.
  • 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.

Rollback Steps

  • This feature can be disabled by running the following Chatops command:
/chatops run feature set track_gitlab_schema_in_current_transaction false
Edited by Thong Kuah