Add notes to the Sidekiq and Container Registry documentation

doc/administration/packages/container_registry.md

@@ -824,6 +824,13 @@ notifications:
 
 ## Run the Cleanup policy now
 
+WARNING:
+If you're using a distributed architecture and Sidekiq is running on a different node, the cleanup
+policies don't work. To fix this, you must configure the `gitlab.rb` file on the Sidekiq nodes to
+point to the correct registry URL and copy the `registry.key` file to each Sidekiq node. For more
+information, see the [Sidekiq configuration](../sidekiq.md)
+page.
+
 To reduce the amount of [Container Registry disk space used by a given project](../troubleshooting/gitlab_rails_cheat_sheet.md#registry-disk-space-usage-by-project),
 administrators can clean up image tags
 and [run garbage collection](#container-registry-garbage-collection).

doc/administration/sidekiq.md

@@ -94,6 +94,16 @@ you want using steps 1 and 2 from the GitLab downloads page.
    gitlab_exporter['enable'] = false
    ```
 
+1. If you're using the Container Registry and it's running on a different node than Sidekiq, then
+   configure the registry URL:
+
+   ```ruby
+   registry_external_url 'https://registry.example.com'
+   gitlab_rails['registry_api_url'] = "https://registry.example.com"
+   ```
+  
+   You must also copy the `registry.key` file to each Sidekiq node.
+
 1. Run `gitlab-ctl reconfigure`.
 
 You will need to restart the Sidekiq nodes after an update has occurred and database
@@ -180,6 +190,10 @@ node_exporter['listen_address'] = '10.10.1.48:9100'
 
 # Rails Status for prometheus
 gitlab_rails['monitoring_whitelist'] = ['10.10.1.42', '127.0.0.1']
+
+# Container Registry URL for cleanup jobs
+registry_external_url 'https://registry.example.com'
+gitlab_rails['registry_api_url'] = "https://registry.example.com"
 ```
 
 ## Further reading