Deploy to clusters for a project's groups

Look for matching clusters starting from the closest ancestor, then go
up the ancestor tree.

Then use Ruby to get clusters for each group in order. Not that
efficient, considering we will doing up to `NUMBER_OF_ANCESTORS_ALLOWED`
number of queries, but it's a finite number

Explicitly order query by depth

This allows us to control ordering explicitly and also to reverse the
order which is useful to allow us to be consistent with
Clusters::Cluster.on_environment (EE) which does reverse ordering.

Puts querying group clusters behind Feature Flag. Just in case we have
issues with performance, we can easily disable this

1 files changed, 10 insertions, 0 deletions

diff --git a/app/models/clusters/cluster.rb b/app/models/clusters/cluster.rb
index 13906c903b9..a3d26d62a22 100644
--- a/app/models/clusters/cluster.rb
+++ b/app/models/clusters/cluster.rb
@@ -86,6 +86,16 @@ module Clusters
 
     scope :default_environment, -> { where(environment_scope: DEFAULT_ENVIRONMENT) }
 
+    # Returns an ordered list of group clusters order from clusters of closest
+    # group up to furthest ancestor group
+    def self.ordered_group_clusters_for_project(project_id)
+      project_groups = ::Group.joins(:projects).where(projects: { id: project_id })
+      hierarchy_groups = Gitlab::GroupHierarchy.new(project_groups)
+        .base_and_ancestors(depth: :desc)
+
+      hierarchy_groups.flat_map(&:clusters)
+    end
+
     def status_name
       if provider
         provider.status_name