Add missing sharding keys

db/docs/pages_domain_acme_orders.yml

@@ -8,3 +8,12 @@ description: Stores ACME order information used in obtaining Let's Encrypt certi
 introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/14014
 milestone: '12.0'
 gitlab_schema: gitlab_main
+desired_sharding_key:
+  project_id:
+    references: projects
+    backfill_via:
+      parent:
+        foreign_key: pages_domain_id
+        table: pages_domains
+        sharding_key: project_id
+        belongs_to: pages_domain

db/docs/pages_domains.yml

@@ -8,3 +8,5 @@ description: Store Pages domain, certificate and encryption meta data.
 introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/173
 milestone: '8.5'
 gitlab_schema: gitlab_main
+sharding_key:
+  project_id: projects

spec/lib/gitlab/database/sharding_key_spec.rb

@@ -21,7 +21,8 @@
     [
       *tables_with_alternative_not_null_constraint,
       'labels.project_id', # https://gitlab.com/gitlab-org/gitlab/-/issues/434356
-      'labels.group_id' # https://gitlab.com/gitlab-org/gitlab/-/issues/434356
+      'labels.group_id', # https://gitlab.com/gitlab-org/gitlab/-/issues/434356
+      'pages_domains.project_id' # https://gitlab.com/gitlab-org/gitlab/-/issues/442178
     ]
   end