Add manual sync instructions for Geo container registry

doc/administration/geo/disaster_recovery/planned_failover.md

@@ -42,6 +42,38 @@ Repository-centric strategies for using `rsync` effectively can be found in the
 [moving repositories](../../operations/moving_repositories.md) documentation; these strategies can
 be adapted for use with any other file-based data, such as [GitLab Pages](../../pages/index.md#change-storage-path).
 
+### Container registry
+
+By default, the container registry is not automatically replicated to secondary
+sites and this needs to be manually configured, see [Docker Registry for a secondary site](../replication/docker_registry.md).
+
+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:
+
+```shell
+# 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](../../../raketasks/backup_restore.md#back-up-gitlab)
+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](../../../raketasks/backup_restore.md#excluding-specific-directories-from-the-backup):
+
+   ```shell
+   # 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
+   ```
+
+1. Copy the backup tarball generated from your primary site to the `/var/opt/gitlab/backups` folder
+on your secondary site.
+
+1. On your secondary site, restore the registry following the [Restore GitLab](../../../raketasks/backup_restore.md#restore-gitlab)
+documentation.
+
 ## Preflight checks
 
 NOTE: