Migrate ClickHouse staging data to the new instance

Production Change

Change Summary

Related OKR: https://gitlab.com/gitlab-com/gitlab-OKRs/-/work_items/6669

We use ClickHouse Cloud instances for implementing analytical features within the GitLab application. We have a ClickHouse service configured for staging. Unfortunately, when we set up the service, us-east1 was not available so the instance was set up in us-central1. To reduce the latency between GitLab application servers and ClickHouse we would like to migrate the data to a newly created ClickHouse server.

I'd suggest to run the migration synchronously via a zoom call.

High-level steps:

1. Disable data-ingestion related feature flags so the source DB won't get new writes.
2. Invoke the migrator script on a node where rails console is available to copy data from the source DB to the target DB.
3. Re-configure the staging ClickHouse configuration variables to point to the target DB. (https://gitlab.com/gitlab-com/gl-infra/k8s-workloads/gitlab-com/-/blob/8e3d114c81a043d6055b032b93292f2866486cb8/releases/gitlab/values/gstg.yaml.gotmpl#L1784)
4. Verify the migrated data.
5. Enable data-ingestion related feature flags.

Prerequisites:

• Secrets, usernames and hosts are known.
• Connectivity between the two DBs is working (from source to target).
• The rails application is available on the host (invoking the rails runner command works).
• Both DB has the same DB structure (tables, materialized views). ( @ahegyi ensures this prior the migration)

Change Details

1. Services Impacted - ServiceWeb ServiceSidekiq
2. Change Technician - @jcstephenson
3. Change Reviewer - @gsgl
4. Time tracking - Time, in minutes, needed to execute all change steps, including rollback
5. Downtime Component - If there is a need for downtime, include downtime estimate here

Detailed steps for the change

Change Steps - steps to take to execute the change

Estimated Time to Complete (mins) - 30 minutes

• Set label changein-progress /label ~change::in-progress

• Enable the suspend_click_house_data_ingestion ops feature flag on staging only (#staging slack channel).

     /chatops run feature set suspend_click_house_data_ingestion true --staging

• @ahegyi, verifies that no data ingestion happens.

• Start a console session to a node where rails console is available.

• Clone the migrator script and invoke it in a screen or tmux session. On staging the script will finish in a few minutes (credentials will be provided via shared secrets). @ahegyi provides a shared note via 1password so we can easily invoke it in rails console

• @ahegyi verifies the data by counting records on both DBs

  SELECT *
  FROM
      (
          (
              SELECT
                  'events' as table,
                  (
                      select
                          count(*)
                      from
                          events final
                  ) as count
          )
          UNION ALL
              (
                  SELECT
                      'ci_finished_builds' as table,
                      (
                          select
                              count(*)
                          from
                              ci_finished_builds final
                      ) as count
              )
          UNION ALL
              (
                  SELECT
                      'audit_events' as table,
                      (
                          select
                              count(*)
                        from
                            audit_events final
                    ) as count
            )
        UNION ALL
            (
                SELECT
                    'sync_cursors' as table,
                    (
                        select
                            count(*)
                        from
                            sync_cursors final
                    ) as count
            )
        UNION ALL
            (
                SELECT
                    'code_suggestion_usages' as table,
                    (
                        select
                            count(*)
                        from
                            code_suggestion_usages final
                    ) as count
            )
    ) data
    ORDER BY
    table

• Reconfigure staging to use the new ClickHouse server (https://gitlab.com/gitlab-com/gl-infra/k8s-workloads/gitlab-com/-/blob/8e3d114c81a043d6055b032b93292f2866486cb8/releases/gitlab/values/gstg.yaml.gotmpl#L1784)

• @ahegyi verifies the connectivity by visiting the contribution analytics page. (https://staging.gitlab.com/groups/gitlab-org/-/contribution_analytics)

• Disable the suspend_click_house_data_ingestion ops feature flag on staging (#staging slack channel).

     /chatops run feature delete suspend_click_house_data_ingestion true --staging

• @ahegyi verifies that the background jobs are working via kibana.

• Set label changecomplete /label ~change::complete

Rollback

Rollback steps - steps to be taken in the event of a need to rollback this change

Estimated Time to Complete (mins) - 10 minutes

The migration can be stopped at any step. If something does not work after the new ClickHouse database is set up, we need to reconfigure the old values.

• Reconfigure staging to use the old ClickHouse server (https://gitlab.com/gitlab-com/gl-infra/k8s-workloads/gitlab-com/-/blob/master/releases/gitlab/values/gstg.yaml.gotmpl?ref_type=heads#L1731)
• Set label changeaborted /label ~change::aborted

Monitoring

Key metrics to observe

The disabled workers can be verified via kibana, once the suspend_click_house_data_ingestion feature flag is enabled we shouldn't see jobs scheduled:

1. Go to kibana
2. Select pubsub-sidekiq-inf-gprd* index
3. Filter for json.class.name is ClickHouse::EventsSyncWorker
4. You shouldn't see a new job appearing (worker is scheduled in every 3 minutes)

Apart from this, there is not much to monitor. @ahegyi, will keep an eye on ClickHouse metrics on ClickHouse Cloud console.

Change Reviewer checklist

C4 C3 C2 C1:

• Check if the following applies:
  • The scheduled day and time of execution of the change is appropriate.
  • The change plan is technically accurate.
  • The change plan includes estimated timing values based on previous testing.
  • The change plan includes a viable rollback plan.
  • The specified metrics/monitoring dashboards provide sufficient visibility for the change.

C2 C1:

• Check if the following applies:
  • The complexity of the plan is appropriate for the corresponding risk of the change. (i.e. the plan contains clear details).
  • The change plan includes success measures for all steps/milestones during the execution.
  • The change adequately minimizes risk within the environment/service.
  • The performance implications of executing the change are well-understood and documented.
  • The specified metrics/monitoring dashboards provide sufficient visibility for the change.
    • If not, is it possible (or necessary) to make changes to observability platforms for added visibility?
  • The change has a primary and secondary SRE with knowledge of the details available during the change window.
  • The change window has been agreed with Release Managers in advance of the change. If the change is planned for APAC hours, this issue has an agreed pre-change approval.
  • The labels blocks deployments and/or blocks feature-flags are applied as necessary.

Change Technician checklist

• Check if all items below are complete:
  • The change plan is technically accurate.
  • This Change Issue is linked to the appropriate Issue and/or Epic
  • Change has been tested in staging and results noted in a comment on this issue.
  • A dry-run has been conducted and results noted in a comment on this issue.
  • The change execution window respects the Production Change Lock periods.
  • For C1 and C2 change issues, the change event is added to the GitLab Production calendar.
  • For C1 and C2 change issues, the SRE on-call has been informed prior to change being rolled out. (In #production channel, mention @sre-oncall and this issue and await their acknowledgement.)
  • For C1 and C2 change issues, the SRE on-call provided approval with the eoc_approved label on the issue.
  • For C1 and C2 change issues, the Infrastructure Manager provided approval with the manager_approved label on the issue.
  • Release managers have been informed prior to any C1, C2, or blocks deployments change being rolled out. (In #production channel, mention @release-managers and this issue and await their acknowledgment.)
  • There are currently no active incidents that are severity1 or severity2
  • If the change involves doing maintenance on a database host, an appropriate silence targeting the host(s) should be added for the duration of the change.