[Feature flag] Control migration of exclusive lease from SharedState to ClusterSharedState
Summary
This issue is to rollout the feature on production, that is currently behind the enable_exclusive_lease_double_lock_rw
and use_cluster_shared_state_for_exclusive_lease
feature flag.
Refer to below CRs for the rollout details:
- GSTG - gitlab-com/gl-infra/production#16321 (closed)
- GPRD - gitlab-com/gl-infra/production#16446 (closed)
Owners
- Team: Scalability
- Most appropriate slack channel to reach out to:
#g_scalability
- Best individual to reach out to: @schin1 @marcogreg
- PM: NAME_OF_PM
Stakeholders
Expectations
What are we expecting to happen?
If an existing lease is held (i.e. key exists in old Redis store):
phase | enable_exclusive_lease_double_lock_rw |
use_cluster_shared_state_for_exclusive_lease |
behaviour when try_obtain is called |
---|---|---|---|
1 | false | false | tries to setnx on the key in SS, fails, and returns false |
2 | true | false | tries to setnx on the key in SS, fails, and returns false |
3 | true | true | checks if key exists in SS, which it does, returns false |
To enter phase 2: enable enable_exclusive_lease_double_lock_rw
, it will take roughly 1 minute for the Rails application's in-memory cache to expire and update. The updated apps will start obtaining 2 separate locks when ExclusiveLease
runs try_obtain
.
To enter phase 3: enable use_cluster_shared_state_for_exclusive_lease
, the updated apps will use the new Redis data store when obtaining leases.
We should remain in phase 2 for a minimum duration (~5-10 minute at least) before switching to phase 3 as rollback may be difficult. Note that going from phase 1 to 3 is safe (if the app ensure
s a .cancel
to release the lease) but we cannot roll back to phase 1 safely. It is safer to go 1 -> 2 -> 3
and back.
This diagram summarises the behaviour at different states and the transitions.
When is the feature viable?
NIl
What might happen if this goes wrong?
There could be deadlocks that require waiting for the duration of the lease before any actors can obtain it. But that is highly unlikely since the different stages of migration are listed above and reviewed in detail.
What can we monitor to detect problems with this?
Monitor the rate of lock acquisition failure (FailedToObtainLockError
) we can roughly estimate this by checking sidekiq logs for lock
keyword in error messages.
Consider mentioning checks for 5xx errors or other anomalies like an increase in redirects (302 HTTP response status)
What can we check for monitoring production after rollouts?
Consider adding links to check for Sentry errors, Production logs for 5xx, 302s, etc.
Check sidekiq error rates and request rates via the overview dashboard.
Check redis-cluster-shared-state
service dashboard for the increase in request rates after either flags are enabled.
Check redis
service dashboard for a drop in request rate after use_cluster_shared_state_for_exclusive_lease
is enabled. The drop in request rate is due to the reduction in SETNX
being used. There will still be some exclusive-lease-related traffic since writes like cancel
and renew
are still happening.
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. -
Verify that the feature MRs have been deployed to non-production environments with: -
/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 --staging --staging-ref
-
If the feature flag causes QA end-to-end tests to fail: -
Disable the feature flag on staging to avoid blocking deployments.
-
-
-
Verify that the feature works as expected. Posting the QA result in this issue is preferable. The best environment to validate the feature in is staging-canary as this is the first environment deployed to. Note you will need to make sure you are configured to use canary as outlined here when accessing the staging environment in order to make sure you are testing appropriately.
For assistance with QA end-to-end test failures, please reach out via the #quality
Slack channel. Note that QA test failures on staging-ref don't block deployments.
Specific 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
).
-
Ensure that the feature MRs have been deployed to both production and canary. -
/chatops run auto_deploy status <merge-commit-of-your-feature>
- Depending on the type of actor you are using, pick one of these options:
- If you're using project-actor, you must enable the feature on these entries:
-
/chatops run feature set --project=gitlab-org/gitlab,gitlab-org/gitlab-foss,gitlab-com/www-gitlab-com <feature-flag-name> true
-
- If you're using group-actor, you must enable the feature on these entries:
-
/chatops run feature set --group=gitlab-org,gitlab-com <feature-flag-name> true
-
- If you're using user-actor, you must enable the feature on these entries:
-
/chatops run feature set --user=<your-username> <feature-flag-name> true
-
- If you're using project-actor, you must enable the feature on these entries:
-
-
Verify that the feature works on the specific entries. Posting the QA result in this issue is preferable.
Preparation before global rollout
-
Set a milestone to the 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 has been updated (More info). -
Leave a comment on the feature issue announcing estimated time when this feature flag will be enabled on GitLab.com. -
Ensure that any breaking changes have been announced following the release post process to ensure GitLab customers are aware. -
Notify #support_gitlab-com
and your team channel (more guidance when this is necessary in the dev docs). -
Ensure that the feature flag rollout plan is reviewed by another developer familiar with the domain.
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. -
Between every step wait for at least 15 minutes and monitor the appropriate graphs on https://dashboards.gitlab.net. -
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> --random
-
- Enable the feature globally on production environment.
-
/chatops run feature set <feature-flag-name> true
-
-
-
-
Observe appropriate graphs on https://dashboards.gitlab.net and verify that services are not affected. -
Leave a comment on the feature issue announcing 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 totrue
. -
Review what warrants a changelog entry and decide if a 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 run release check <merge-request-url> <milestone>
-
-
Consider cleaning up the feature flag from all environments by running these chatops command in #production
channel. Otherwise these settings may override the default enabled.-
/chatops run feature delete <feature-flag-name> --dev --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 "[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.
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 <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 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 run release check <merge-request-url> <milestone>
-
-
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 --staging --staging-ref --production
-
-
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