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[Feature flag] Improve efficiency of IID generation for pipelines

Summary

This issue is to rollout Improve the efficiency of non-strictly monotonic (non-gapless) IIDs for pipelines on production, that is currently behind the generate_iids_without_explicit_locking feature flag.

Owners

Stakeholders

The Rollout Plan

  • Due to the way the way IIDs are generated, this is a global feature flag.
  • Rollout first on GitLab.com, and monitor for issues.
  • After confidence is high this does not cause any issues, remove the feature flag.

Testing Groups/Projects/Users

This is a global feature flag

Expectations

What are we expecting to happen?

IID generation should continue uninterrupted, but we should hopefully see less contention creating pipelines in a threaded environment (sidekiq).

What might happen if this goes wrong?

A problem with this flag could affect any objects which rely on IID creation:

issues
merge_requests
deployments
milestones
epics
ci_pipelines
operations_feature_flags
operations_user_lists
alert_management_alerts
sprints
design_management_designs
incident_management_oncall_schedules

At that point, the feature flag should be disabled to revert to the old behavior.

What can we monitor to detect problems with this?

Rollout Steps

Rollout on non-production environments

  • Ensure that the feature MRs have been deployed to non-production environments.
    • /chatops run auto_deploy status 40735f54656a6703d67e5e72933eef670ffd736f
  • Enable the feature globally on non-production environments.
    • /chatops run feature set generate_iids_without_explicit_locking true --dev
    • /chatops run feature set generate_iids_without_explicit_locking true --staging
  • Verify that the feature works as expected. Posting the QA result in this issue is preferable.

Preparation before production rollout

  • Ensure that the feature MRs have been deployed to both production and canary.
    • /chatops run auto_deploy status 40735f54656a6703d67e5e72933eef670ffd736f
  • 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.
  • If the feature might impact the user experience, notify #support_gitlab-com and your team channel (more guidance when this is necessary in the dev docs).
  • If the feature flag in code has an actor, enable it on GitLab.com for testing groups/projects.
    • /chatops run feature set --<actor-type>=<actor> <feature-flag-name> true
  • Verify that the feature works as expected. Posting the QA result in this issue is preferable.

Global rollout on production

  • Incrementally roll out the feature.
    • If the feature flag in code has an actor, perform actor-based rollout.
      • /chatops run feature set <feature-flag-name> <rollout-percentage> --actors
    • If the feature flag in code does NOT have an actor, perform time-based rollout (random rollout).
      • /chatops run feature set generate_iids_without_explicit_locking <rollout-percentage>
    • Enable the feature globally on production environment.
      • /chatops run feature set generate_iids_without_explicit_locking 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 generate_iids_without_explicit_locking 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 generate_iids_without_explicit_locking --dev
    • /chatops run feature delete generate_iids_without_explicit_locking --staging
    • /chatops run feature delete generate_iids_without_explicit_locking
  • Close this rollout issue.

Rollback Steps

  • This feature can be disabled by running the following Chatops command:
/chatops run feature set generate_iids_without_explicit_locking false
Edited by Patrick Bair