Docker Registry for a secondary site

You can set up a Docker Registry on your secondary Geo site that mirrors the one on the primary Geo site.

Storage support

Docker Registry currently supports a few types of storage. If you choose a distributed storage (azure, gcs, s3, swift, or oss) for your Docker Registry on the primary site, you can use the same storage for a secondary Docker Registry as well. For more information, read the Load balancing considerations when deploying the Registry, and how to set up the storage driver for the GitLab integrated Container Registry.

Replicating Docker Registry

You can enable a storage-agnostic replication so it can be used for cloud or local storage. Whenever a new image is pushed to the primary site, each secondary site pulls it to its own container repository.

To configure Docker Registry replication:

Configure the primary site.
Configure the secondary site.
Verify Docker Registry replication.

Configure primary site

Make sure that you have Container Registry set up and working on the primary site before following the next steps.

We need to make Docker Registry send notification events to the primary site.

SSH into your GitLab primary server and login as root:
```
sudo -i
```
Edit /etc/gitlab/gitlab.rb:
```
registry['notifications'] = [
  {
    'name' => 'geo_event',
    'url' => 'https://example.com/api/v4/container_registry_event/events',
    'timeout' => '500ms',
    'threshold' => 5,
    'backoff' => '1s',
    'headers' => {
      'Authorization' => ['<replace_with_a_secret_token>']
    }
  }
]
```
Replace <replace_with_a_secret_token> with a case sensitive alphanumeric string that starts with a letter. You can generate one with < /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c 32 | sed "s/^[0-9]*//"; echo

If you use an external Registry (not the one integrated with GitLab), you must add these settings to its configuration yourself. In this case, you also have to specify notification secret in registry.notification_secret section of /etc/gitlab/gitlab.rb file.

If you use GitLab HA, you also have to specify the notification secret in registry.notification_secret section of /etc/gitlab/gitlab.rb file for every web node.
Reconfigure the primary node for the change to take effect:
```
gitlab-ctl reconfigure
```

Configure secondary site

Make sure you have Container Registry set up and working on the secondary site before following the next steps.

The following steps should be done on each secondary site you’re expecting to see the Docker images replicated.

Because we need to allow the secondary site to communicate securely with the primary site Container Registry, we need to have a single key pair for all the sites. The secondary site uses this key to generate a short-lived JWT that is pull-only-capable to access the primary site Container Registry.

For each application and Sidekiq node on the secondary site:

SSH into the node and login as the root user:
```
sudo -i
```
Copy /var/opt/gitlab/gitlab-rails/etc/gitlab-registry.key from the primary to the node.

Edit /etc/gitlab/gitlab.rb and add:

gitlab_rails['geo_registry_replication_enabled'] = true
   
# Primary registry's hostname and port, it will be used by
# the secondary node to directly communicate to primary registry
gitlab_rails['geo_registry_replication_primary_api_url'] = 'https://primary.example.com:5050/' 

Reconfigure the node for the change to take effect:
```
gitlab-ctl reconfigure
```

Verify replication

To verify Container Registry replication is working, on the secondary site:

On the top bar, select Menu > Admin.
On the left sidebar, select Geo > Nodes. The initial replication, or “backfill”, is probably still in progress.

You can monitor the synchronization process on each Geo site from the primary site’s Geo Nodes dashboard in your browser.