1 files changed, 3 insertions, 0 deletions
diff --git a/app/services/clusters/applications/prometheus_update_service.rb b/app/services/clusters/applications/prometheus_update_service.rb
index 437f6ab1202..b8b50f06d72 100644
--- a/app/services/clusters/applications/prometheus_update_service.rb
+++ b/app/services/clusters/applications/prometheus_update_service.rb
@@ -2,6 +2,7 @@
 
 module Clusters
   module Applications
+    # Deprecated, to be removed in %14.0 as part of https://gitlab.com/groups/gitlab-org/-/epics/4280
     class PrometheusUpdateService < BaseHelmService
       attr_accessor :project
 
@@ -11,6 +12,8 @@ module Clusters
       end
 
       def execute
+        raise NotImplementedError, 'Externally installed prometheus should not be modified!' unless app.managed_prometheus?
+
         app.make_updating!
 
         helm_api.update(patch_command(values))