[Feature flag] Rollout of `sidekiq_load_balancing_rotate_up_to_date_replica`
Summary
This issue is to rollout Improve finding caught up replica for SidekiqServerMiddleware on production,
that is currently behind the sidekiq_load_balancing_rotate_up_to_date_replica
feature flag.
Owners
- Team: Memory
- Most appropriate slack channel to reach out to:
#g_memory
- Best individual to reach out to:
@alipniagov
/@nmilojevic1
- PM:
@fzimmer
The Rollout Plan
- Rollout on GitLab.com - will roll back if any issues with the Sidekiq Load balancing behavior will be noticed.
Expectations
What are we expecting to happen?
We should apply a better algorithm for picking up a replica for the workers utilizing LB.
This should reduce the total number of retries happening, in theory, as we will search for caught-up replica and would also shuffle them every time.
In reality, it may not be very noticeable, at least on the short span, as it depends on the statistical probability of replicas being caught up and the percentage of such during the worker execution.
What might happen if this goes wrong?
In theory, a replica picking mechanism could be working wrong, even though we don't expect it. In that case, we should still fall back to primary, so it wouldn't interrupt job execution.
What can we monitor to detect problems with this?
- Database chosen - retries count
- Sidekiq overview
- Kibana worker logs - we could check various workers
- Sidekiq Queue Detail - for multiple queues, or general
- Sidekiq Worker Detail - e.g. for BuildQueueWorker
- Replica pool saturation
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>
-
-
Enable the feature globally on non-production environments. -
/chatops run feature set <feature-flag-name> true --dev
-
/chatops run feature set <feature-flag-name> true --staging
-
-
Verify that the feature works as expected. Posting the QA result in this issue is preferable.
Preparation before production rollout
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Ensure that the feature MRs have been deployed to both production and canary. -
/chatops run auto_deploy status <merge-commit-of-your-feature>
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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 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 <feature-flag-name> <rollout-percentage>
-
- Enable the feature globally on production environment.
-
/chatops run feature set <feature-flag-name> true
-
- If the feature flag in code has an actor, perform actor-based rollout.
-
Announce on the feature issue that the feature has been globally enabled. -
Cross-post chatops slack command to #support_gitlab-com
. (more guidance when this is necessary in the dev docs) and in your team channel -
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 totrue
. - [-] Create a changelog entry.
- [-] Set the
- [-] Ensure that the above 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>
- [-]
- [-] Close the feature issue to indicate the feature will be released in the current milestone.
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 above 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>
-
-
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
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/chatops run feature delete <feature-flag-name>
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-
Close this rollout issue.
Rollback Steps
-
This feature can be disabled by running the following Chatops command:
/chatops run feature set sidekiq_load_balancing_rotate_up_to_date_replica false