Docker Registry for a secondary node (PREMIUM ONLY)

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

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 node, 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 node, each secondary node will pull it to its own container repository.

To configure Docker Registry replication:

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

Configure primary node

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

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

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>']
    }
  }
]
```
NOTE: 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

NOTE: 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 will also have to specify notification secret in registry.notification_secret section of /etc/gitlab/gitlab.rb file.

NOTE: If you use GitLab HA, you will 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 node

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

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

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

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

Edit /etc/gitlab/gitlab.rb:

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

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

Verify replication

To verify Container Registry replication is working, go to Admin Area > Geo (/admin/geo/nodes) on the secondary node. The initial replication, or "backfill", will probably still be in progress. You can monitor the synchronization process on each Geo node from the primary node's Geo Nodes dashboard in your browser.