Handle invalid repositories in Docker Registry correctly

changelogs/unreleased/196158-fix-tags-nil.yml

+---
+title: 'Geo: Handle repositories in Docker Registry with no tags gracefully'
+merge_request: 23022
+author:
+type: fixed

ee/app/services/geo/container_repository_sync.rb

@@ -55,10 +55,11 @@ module Geo
 
     def primary_tags
       @primary_tags ||= begin
-        tags = client.repository_tags(name)['tags']
-        return [] if tags.nil?
+        manifest = client.repository_tags(name)
 
-        tags.map do |tag|
+        return [] unless manifest && manifest['tags']
+
+        manifest['tags'].map do |tag|
           { name: tag, digest: client.repository_tag_digest(name, tag) }
         end
       end

ee/spec/services/geo/container_repository_sync_spec.rb

@@ -84,5 +84,20 @@ describe Geo::ContainerRepositorySync, :geo do
 
       described_class.new(container_repository).execute
     end
+
+    context 'when primary repository has no tags' do
+      it 'considers the primary repository empty and does not fail' do
+        stub_request(:get, "http://primary.registry.gitlab/v2/group/test/my_image/tags/list")
+          .with(
+            headers: { 'Authorization' => 'bearer pull-token' })
+          .to_return(
+            status: 200,
+            headers: { 'Content-Type' => 'application/json' })
+
+        expect(container_repository).to receive(:delete_tag_by_digest).with('sha256:aaaaa')
+
+        described_class.new(container_repository).execute
+      end
+    end
   end
 end