FF rollout of diff_blob_metadata_only_for_code_review_id

Summary

This issue is to roll out the feature on production, that is currently behind the diff_blob_metadata_only_for_code_review_id feature flag.

Owners

• Most appropriate Slack channel to reach out to: #g_source_code
• Best individual to reach out to: @ghinfey

Expectations

What are we expecting to happen?

code_review_id will use blob OIDs (from_id/to_id) already available in Gitaly's CommitDiffResponse instead of triggering a separate GetBlobs RPC that fetches up to 512KB of content per file. For streamed diffs (commit, compare) this eliminates the extra Gitaly calls entirely. For persisted diffs (MR) it falls back to the existing blob&.id behaviour. This addresses GRPC::DeadlineExceeded and ActiveRecord::QueryCanceled errors on the diff_files_metadata endpoint for large diffs.

What can go wrong and how would we detect it?

• "Mark file as viewed" state could reset if from_id/to_id from the diff response differs from the value returned by blob&.id (unlikely — both represent the same git blob OID)
• Monitor Sentry for new errors on diff_files_metadata endpoints
• Monitor Gitaly dashboard for any unexpected changes in RPC patterns

Rollout Steps

Note: Please make sure to run the chatops commands in the Slack channel that gets impacted by the command.

Rollout on non-production environments

• Verify the MR with the feature flag is merged to master and has been deployed to non-production environments with /chatops gitlab run auto_deploy status <merge-commit-of-your-feature>
• Deploy the feature flag at a percentage (recommended percentage: 50%) with /chatops gitlab run feature set diff_blob_metadata_only_for_code_review_id 50 --actors --dev --pre --staging --staging-ref
• Monitor that the error rates did not increase (repeat with a different percentage as necessary).
• Enable the feature globally on non-production environments with /chatops gitlab run feature set diff_blob_metadata_only_for_code_review_id true --dev --pre --staging --staging-ref
• Verify that the feature works as expected. The best environment to validate the feature in is staging-canary as this is the first environment deployed to. Make sure you are configured to use canary.
• If the feature flag causes end-to-end tests to fail, disable the feature flag on staging to avoid blocking deployments.
  • See #e2e-run-staging Slack channel and look for the following messages:
    • test kicked off: Feature flag diff_blob_metadata_only_for_code_review_id has been set to true on **gstg**
    • test result: This pipeline was triggered due to toggling of diff_blob_metadata_only_for_code_review_id feature flag If you encounter end-to-end test failures and are unable to diagnose them, you may reach out to the #s_developer_experience Slack channel for assistance. Note that end-to-end test failures on staging-ref don't block deployments.

Before production rollout

• If the change is significant and you wanted to announce in #whats-happening-at-gitlab, it best to do it before rollout to gitlab-org/gitlab-com.

Specific rollout on production

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

• Ensure that the feature MRs have been deployed to both production and canary with /chatops gitlab run auto_deploy status <merge-commit-of-your-feature>
• Depending on the type of actor you are using, pick one of these options:
  • For project-actor: /chatops gitlab run feature set --project=gitlab-org/gitlab,gitlab-org/gitlab-foss,gitlab-com/www-gitlab-com diff_blob_metadata_only_for_code_review_id true
  • For group-actor: /chatops gitlab run feature set --group=gitlab-org,gitlab-com diff_blob_metadata_only_for_code_review_id true
  • For user-actor: /chatops gitlab run feature set --user=ghinfey diff_blob_metadata_only_for_code_review_id true
  • For all internal users: /chatops gitlab run feature set --feature-group=gitlab_team_members diff_blob_metadata_only_for_code_review_id true
• Verify that the feature works for the specific actors.

Preparation before global rollout

• Set a milestone to this rollout issue to signal for enabling and removing the feature flag when it is stable.
• 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 exists for the feature, and the version history text has been updated.
• Ensure that any breaking changes have been announced following the release post process to ensure GitLab customers are aware.
• Notify the #support_gitlab-com Slack channel and your team channel (more guidance when this is necessary in the dev docs).
• If this flag is or may be queried by external API consumers (for example, IDE extensions, Duo CLI, or CI integrations), follow the external API consumer guidance and ensure a fail-open mechanism is in place before the rollout milestone is finalised.

Global rollout on production

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

• Incrementally roll out the feature on production.
  • Example: /chatops gitlab run feature set diff_blob_metadata_only_for_code_review_id <rollout-percentage> --actors.
  • Between every step wait for at least 15 minutes and monitor the appropriate graphs on https://dashboards.gitlab.net.
• After the feature has been 100% enabled, wait for at least one day before releasing the feature.

(Optional) Release the feature with the feature flag

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.

See instructions if you're sure about enabling the feature globally through the feature flag definition

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. - [ ] If feature was enabled for various actors, ensure the feature has been enabled globally on production `/chatops gitlab run feature get diff_blob_metadata_only_for_code_review_id`. If the feature has not been globally enabled then enable the feature globally using: `/chatops gitlab run feature set diff_blob_metadata_only_for_code_review_id true` - [ ] Set the default_enabled attribute in the feature flag definition to `true`. - [ ] Decide which changelog entry is needed. - [ ] Ensure that the default-enabling MR has been included in the release package. If the merge request was deployed before the monthly release was tagged, the feature can be officially announced in a release blog post: `/chatops gitlab run release check ` - [ ] After the default-enabling MR has been deployed, clean up the feature flag from all environments by running these chatops command in the `#production` channel: `/chatops gitlab run feature delete diff_blob_metadata_only_for_code_review_id --dev --pre --staging --staging-ref --production` - [ ] 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 "[FF] `diff_blob_metadata_only_for_code_review_id` - Cleanup". - [ ] Execute the `/copy_metadata ` quick action to copy the labels from this rollout issue. - [ ] Link this rollout issue as a related issue. - [ ] Close this rollout issue.

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. You can either create a follow-up issue for Feature Flag Cleanup or use the checklist below in this same issue.

• Create a merge request to remove the diff_blob_metadata_only_for_code_review_id feature flag. Ask for review/approval/merge as usual. The MR should include the following changes:
  • Remove all references to the feature flag from the codebase.
  • Remove the YAML definitions for the feature from the repository.
• Ensure that the cleanup MR has been included in the release package. If the merge request was deployed before the monthly release was tagged, the feature can be officially announced in a release blog post: /chatops gitlab run release check <merge-request-url> <milestone>
• Close the feature issue to indicate the feature will be released in the current milestone.
• Once the cleanup MR has been deployed to production, clean up the feature flag from all environments by running these chatops command in #production channel: /chatops gitlab run feature delete diff_blob_metadata_only_for_code_review_id --dev --pre --staging --staging-ref --production
• Close this rollout issue.

Rollback Steps

• This feature can be disabled on production by running the following Chatops command: /chatops gitlab run feature set diff_blob_metadata_only_for_code_review_id false
• Disable the feature flag on non-production environments: /chatops gitlab run feature set diff_blob_metadata_only_for_code_review_id false --dev --pre --staging --staging-ref
• Delete feature flag from all environments: /chatops gitlab run feature delete diff_blob_metadata_only_for_code_review_id --dev --pre --staging --staging-ref --production