[Feature flag] Enable `decomposed_ci_query_in_pipelines_for_merge_request_finder`

Summary

This issue is to rollout Fix PipelinesForMergeRequestFinder doing cross-join to projects, merge_requests, commits on production, that is currently behind the decomposed_ci_query_in_pipelines_for_merge_request_finder feature flag.

Owners

• Team: grouppipeline execution
• Most appropriate slack channel to reach out to: #g_pipeline-execution
• Best individual to reach out to: @ck3g
• PM: Cheryl Li @cheryl.li

Stakeholders

The Rollout Plan

• Partial Rollout on GitLab.com with testing groups
• Rollout on GitLab.com for a certain period (How long)
• Percentage Rollout on GitLab.com
• Rollout Feature for everyone as soon as it's ready

Testing Groups/Projects/Users

• gitlab-org/gitlab project
• gitlab-org/gitlab-foss project
• gitlab-com/www-gitlab-com project
• gitlab-org/gitlab-com groups
• ...

Expectations

What are we expecting to happen?

What might happen if this goes wrong?

What can we monitor to detect problems with this?

• https://dashboards.gitlab.net/d/web-rails-controller/web-rails-controller?orgId=1&var-PROMETHEUS_DS=Global&var-environment=gprd&var-stage=main&var-controller=Projects::MergeRequestsController&var-action=pipelines.json
• https://log.gprd.gitlab.net/goto/85a6ad4294f3e3d0a457e52c9b1aded4

From #341341 (comment 696279958)

Rollout Steps

Rollout on non-production environments

• Ensure that the feature MRs have been deployed to non-production environments.
  • /chatops run auto_deploy status 018e51a2ab5057ac4c6fafd0926c8efbcf0f6af5
• Enable the feature globally on non-production environments.
  • /chatops run feature set decomposed_ci_query_in_pipelines_for_merge_request_finder true --dev
  • /chatops run feature set decomposed_ci_query_in_pipelines_for_merge_request_finder 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 018e51a2ab5057ac4c6fafd0926c8efbcf0f6af5
• Check if the feature flag change needs to be accompanied with a change management issue. Cross link the issue here if it does. (doesn't need)
• 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).

Global rollout on production

All /chatops commands that target production should be done in the #production slack channel for visibility.

• Confirm the feature flag is enabled on staging without incident

• Roll out the feature to targeted testing projects/groups first

  • /chatops run feature set --project=gitlab-org/gitlab decomposed_ci_query_in_pipelines_for_merge_request_finder true
  • /chatops run feature set --project=gitlab-org/gitlab-foss decomposed_ci_query_in_pipelines_for_merge_request_finder true
  • /chatops run feature set --project=gitlab-com/www-gitlab-com decomposed_ci_query_in_pipelines_for_merge_request_finder true

• Incrementally roll out the feature.

  • If the feature flag in code has an actor, perform actor-based rollout.
    • /chatops run feature set decomposed_ci_query_in_pipelines_for_merge_request_finder 25 --actors
    • /chatops run feature set decomposed_ci_query_in_pipelines_for_merge_request_finder 50 --actors
    • /chatops run feature set decomposed_ci_query_in_pipelines_for_merge_request_finder 75 --actors
    • /chatops run feature set decomposed_ci_query_in_pipelines_for_merge_request_finder 100 --actors
  • If the feature flag in code does NOT have an actor, perform time-based rollout (random rollout).
    • [-] /chatops run feature set <feature-flag-name> <rollout-percentage>

• Verify the change has the desired outcome with the limited rollout before enabling the feature globally on production.

• Enable the feature globally on production environment. /chatops run feature set <feature-flag-name> 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.
  • Set the default_enabled attribute in the feature flag definition to true.
  • Create a changelog entry.
• 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 70c250478990971e1779c07f95b58ff9e16da5d4
• 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 decomposed_ci_query_in_pipelines_for_merge_request_finder --dev
  • /chatops run feature delete decomposed_ci_query_in_pipelines_for_merge_request_finder --staging
  • /chatops run feature delete decomposed_ci_query_in_pipelines_for_merge_request_finder
• Close this rollout issue.

Rollback Steps

• This feature can be disabled by running the following Chatops command:

/chatops run feature set <feature-flag-name> false