Disaster recovery for planned failover

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The primary use-case of Disaster Recovery is to ensure business continuity in the event of unplanned outage, but it can be used in conjunction with a planned failover to migrate your GitLab instance between regions without extended downtime.

As replication between Geo sites is asynchronous, a planned failover requires a maintenance window in which updates to the primary site are blocked. The length of this window is determined by your replication capacity - when the secondary site is completely synchronized with the primary site, the failover can occur without data loss.

This document assumes you already have a fully configured, working Geo setup. Read this document and the Disaster Recovery failover documentation in full before proceeding. Planned failover is a major operation, and if performed incorrectly, there is a high risk of data loss. Consider rehearsing the procedure until you are comfortable with the necessary steps and have a high degree of confidence in being able to perform them accurately.

Not all data is automatically replicated

If you are using any GitLab features that Geo doesn’t support, you must make separate provisions to ensure that the secondary site has an up-to-date copy of any data associated with that feature. This may extend the required scheduled maintenance period significantly. A list of features supported by Geo can be found in the replicated data types table.

A common strategy for keeping this period as short as possible for data stored in files is to use rsync to transfer the data. An initial rsync can be performed ahead of the maintenance window; subsequent rsyncs (including a final transfer inside the maintenance window) then transfers only the changes between the primary site and the secondary sites.

Git repository-centric strategies for using rsync effectively can be found in the moving repositories documentation; these strategies can be adapted for use with any other file-based data.

Container registry

By default, the container registry is not automatically replicated to secondary sites and this needs to be manually configured, see container registry for a secondary site.

If you are using local storage on your current primary site for the container registry, you can rsync the container registry objects to the secondary site you are about to failover to: 

# Run from the secondary site
rsync --archive --perms --delete root@<geo-primary>:/var/opt/gitlab/gitlab-rails/shared/registry/. /var/opt/gitlab/gitlab-rails/shared/registry

Alternatively, you can back up the container registry on the primary site and restore it onto the secondary site:

  1. On your primary site, back up only the registry and exclude specific directories from the backup: 

    # Create a backup in the /var/opt/gitlab/backups folder
sudo gitlab-backup create SKIP=db,uploads,builds,artifacts,lfs,terraform_state,pages,repositories,packages

  2. Copy the backup tarball generated from your primary site to the /var/opt/gitlab/backups folder on your secondary site.

  3. On your secondary site, restore the registry following the Restore GitLab documentation.

Preflight checks

Run this command to list out all preflight checks and automatically check if replication and verification are complete before scheduling a planned failover to ensure the process goes smoothly: 

gitlab-ctl promotion-preflight-checks

Each step is described in more detail below.

DNS TTL

If you plan to update the primary domain DNS record, you may wish to maintain a low TTL to ensure fast propagation of DNS changes.

Object storage

If you have a large GitLab installation or cannot tolerate downtime, consider migrating to Object Storage before scheduling a planned failover. Doing so reduces both the length of the maintenance window, and the risk of data loss as a result of a poorly executed planned failover.

In GitLab 15.1, you can optionally allow GitLab to manage replication of Object Storage for secondary sites. For more information, see Object Storage replication.

Review the configuration of each secondary site

Database settings are automatically replicated to the secondary site, but the /etc/gitlab/gitlab.rb file must be set up manually, and differs between sites. If features such as Mattermost, OAuth or LDAP integration are enabled on the primary site but not the secondary site, they are lost during failover.

Review the /etc/gitlab/gitlab.rb file for both sites and ensure the secondary site supports everything the primary site does before scheduling a planned failover.

Run system checks

Run the following on both primary and secondary sites: 

gitlab-rake gitlab:check
gitlab-rake gitlab:geo:check

If any failures are reported on either site, they should be resolved before scheduling a planned failover.

Check that secrets and SSH host keys match between nodes

The SSH host keys and /etc/gitlab/gitlab-secrets.json files should be identical on all nodes. Check this by running the following on all nodes and comparing the output: 

sudo sha256sum /etc/ssh/ssh_host* /etc/gitlab/gitlab-secrets.json

If any files differ, manually replicate GitLab secrets and replicate SSH host keys to the secondary site as necessary.

Check that the correct certificates are installed for HTTPS

This step can be safely skipped if the primary site and all external sites accessed by the primary site use public CA-issued certificates.

If the primary site uses custom or self-signed TLS certificates to secure inbound connections or if the primary site connects to external services that use custom or self-signed certificates, the correct certificates should also be installed on the secondary site. Follow instructions for using custom certificates with secondary sites.

Ensure Geo replication is up-to-date

The maintenance window does not end until Geo replication and verification is completely finished. To keep the window as short as possible, you should ensure these processes are close to 100% as possible during active use.

On the secondary site:

  1. On the left sidebar, at the bottom, select Admin.

  2. Select Geo > Sites. Replicated objects (shown in green) should be close to 100%, and there should be no failures (shown in red). If a large proportion of objects aren’t yet replicated (shown in gray), consider giving the site more time to complete

    Geo admin dashboard showing the synchronization status of a secondary site

If any objects are failing to replicate, this should be investigated before scheduling the maintenance window. Following a planned failover, anything that failed to replicate is lost.

A common cause of replication failures is the data being missing on the primary site - you can resolve these failures by restoring the data from backup, or removing references to the missing data.

Verify the integrity of replicated data

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Notify users of scheduled maintenance

On the primary site:

  1. On the left sidebar, at the bottom, select Admin.
  2. Select Messages.
  3. Add a message notifying users on the maintenance window. You can check under Geo > Sites to estimate how long it takes to finish syncing.
  4. Select Add broadcast message.

Runner failover

Depending on how your instance URL is configured, there may be additional steps to keep your runner fleet at 100% after the failover.

The token used to register runners should work on the primary or secondary instances. If you are seeing issues connecting after failover, it is possible that the secrets were not copied over during the secondary configuration. You can reset runner tokens, however, be aware that you may experience other issues unrelated to runners, if secrets are not in sync.

If a runner is repeatedly unable to connect to a GitLab instance, it stops trying to connect for a period of time (default 1 hour). If you would like to avoid this, the runners should be shutdown until the GitLab instance is reachable. See the check_interval documentation, and the configuration options unhealthy_requests_limit and unhealthy_interval.

  • If you are using our Location aware URL, after the old primary is removed from the DNS configuration, runners should automatically connect to the next closest instance.
  • If you are using separate URLs, then any runner connected to the current primary needs to be updated to connect to the new primary, once promoted.
  • If you have any runners connected to your current secondary, see how to handle them during the failover.

Prevent updates to the primary site

To ensure that all data is replicated to a secondary site, updates (write requests) need to be disabled on the primary site:

  1. Enable maintenance mode on the primary site.
  2. On the left sidebar, at the bottom, select Admin.
  3. Select Monitoring > Background jobs.
  4. On the Sidekiq dashboard, select Cron.
  5. Select Disable All to disable non-Geo periodic background jobs.

  6. Select Enable for the following cronjobs:

    • geo_metrics_update_worker
    • geo_prune_event_log_worker
    • geo_verification_cron_worker
    • repository_check_worker

    This re-enables several cron jobs that are essential for planned failover to complete successfully.

Finish replicating and verifying all data

  1. If you are manually replicating any data not managed by Geo, trigger the final replication process now.
  2. On the primary site:
    1. On the left sidebar, at the bottom, select Admin.
    2. On the left sidebar, select Monitoring > Background jobs.
    3. On the Sidekiq dashboard, select Queues, and wait for all queues except those with geo in the name to drop to 0. These queues contain work that has been submitted by your users; failing over before it is completed, causes the work to be lost.

    4. On the left sidebar, select Geo > Sites and wait for the following conditions to be true of the secondary site you are failing over to:

      • All replication meters reach 100% replicated, 0% failures.
      • All verification meters reach 100% verified, 0% failures.
      • Database replication lag is 0 ms.
      • The Geo log cursor is up to date (0 events behind).
  3. On the secondary site:
    1. On the left sidebar, at the bottom, select Admin.
    2. On the left sidebar, select Monitoring > Background jobs.
    3. On the Sidekiq dashboard, select Queues, and wait for all the geo queues to drop to 0 queued and 0 running jobs.
    4. Run an integrity check to verify the integrity of CI artifacts, LFS objects, and uploads in file storage.

At this point, your secondary site contains an up-to-date copy of everything the primary site has, meaning nothing was lost when you fail over.

Promote the secondary site

After the replication is finished, promote the secondary site to a primary site. This process causes a brief outage on the secondary site, and users may need to sign in again. If you follow the steps correctly, the old primary Geo site should still be disabled and user traffic should go to the newly-promoted site instead.

When the promotion is completed, the maintenance window is over, and your new primary site now begins to diverge from the old one. If problems do arise at this point, failing back to the old primary site is possible, but likely to result in the loss of any data uploaded to the new primary in the meantime.

Don’t forget to remove the broadcast message after the failover is complete.

Finally, you can bring the old site back as a secondary.