Database should be read-only in maintenance mode

ee/lib/ee/gitlab/database.rb

@@ -10,7 +10,7 @@ module Database
 
         override :read_only?
         def read_only?
-          ::Gitlab::Geo.secondary?
+          ::Gitlab::Geo.secondary? || ::Gitlab.maintenance_mode?
         end
 
         def healthy?

ee/spec/lib/ee/gitlab/database_spec.rb

@@ -34,6 +34,16 @@
         expect(described_class.read_only?).to be_falsey
       end
     end
+
+    context 'in maintenance mode' do
+      before do
+        stub_application_setting(maintenance_mode: true)
+      end
+
+      it 'returns true' do
+        expect(described_class.read_only?).to be_truthy
+      end
+    end
   end
 
   describe '.healthy?' do