Add logs for ci resource groups

Now logs related to resource group acquisition can be found in
ci_resource_groups_json file

Changelog: added

app/models/ci/resource_group.rb

@@ -29,13 +29,19 @@ def assign_resource_to(processable)
         partition_id: processable.partition_id
       }
 
-      resources.free.limit(1).update_all(attrs) > 0
+      success = resources.free.limit(1).update_all(attrs) > 0
+      log_event(success: success, processable: processable, action: "assign resource to processable")
+
+      success
     end
 
     def release_resource_from(processable)
       attrs = { build_id: nil, partition_id: nil }
 
-      resources.retained_by(processable).update_all(attrs) > 0
+      success = resources.retained_by(processable).update_all(attrs) > 0
+      log_event(success: success, processable: processable, action: "release resource from processable")
+
+      success
     end
 
     def upcoming_processables
@@ -72,5 +78,14 @@ def ensure_resource
       # belong to the same resource group are executed once at time.
       self.resources.build if self.resources.empty?
     end
+
+    def log_event(success:, processable:, action:)
+      Gitlab::Ci::ResourceGroups::Logger.build.info({
+        resource_group_id: self.id,
+        processable_id: processable.id,
+        message: "attempted to #{action}",
+        success: success
+      })
+    end
   end
 end

doc/administration/logs/index.md

@@ -771,6 +771,24 @@ are recorded in this file. For example:
 {"severity":"INFO","time":"2020-11-24T02:31:29.329Z","correlation_id":null,"key":"cd_auto_rollback","action":"remove"}
 ```
 
+## `ci_resource_groups_json.log`
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/384180) in GitLab 15.9.
+
+Depending on your installation method, this file is located at:
+
+- Omnibus GitLab: `/var/log/gitlab/gitlab-rails/ci_resource_group_json.log`
+- Installations from source: `/home/git/gitlab/log/ci_resource_group_json.log`
+
+It contains information about [resource group](../../ci/resource_groups/index.md) acquisition. For example:
+
+```json
+{"severity":"INFO","time":"2023-02-10T23:02:06.095Z","correlation_id":"01GRYS10C2DZQ9J1G12ZVAD4YD","resource_group_id":1,"processable_id":288,"message":"attempted to assign resource to processable","success":true}
+{"severity":"INFO","time":"2023-02-10T23:02:08.945Z","correlation_id":"01GRYS138MYEG32C0QEWMC4BDM","resource_group_id":1,"processable_id":288,"message":"attempted to release resource from processable","success":true}
+```
+
+The examples show the `resource_group_id`, `processable_id`, `message`, and `success` fields for each entry.
+
 ## `auth.log`
 
 > Introduced in GitLab 12.0.

lib/gitlab/ci/resource_groups/logger.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    module ResourceGroups
+      class Logger < ::Gitlab::JsonLogger
+        def self.file_name_noext
+          'ci_resource_groups_json'
+        end
+      end
+    end
+  end
+end