Gitaly feature flag metadata

changelogs/unreleased/gitaly_feature_flag_metadata.yml

+---
+title: Add client and call site metadata to Gitaly calls for better traceability
+merge_request: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14332
+author:
+type: added

lib/gitlab/gitaly_client.rb

@@ -28,6 +28,7 @@ module Gitlab
 
     SERVER_VERSION_FILE = 'GITALY_SERVER_VERSION'.freeze
     MAXIMUM_GITALY_CALLS = 30
+    CLIENT_NAME = (Sidekiq.server? ? 'gitlab-sidekiq' : 'gitlab-web').freeze
 
     MUTEX = Mutex.new
     private_constant :MUTEX
@@ -79,7 +80,16 @@ module Gitlab
 
     def self.request_metadata(storage)
       encoded_token = Base64.strict_encode64(token(storage).to_s)
-      { metadata: { 'authorization' => "Bearer #{encoded_token}" } }
+      metadata = {
+        'authorization' => "Bearer #{encoded_token}",
+        'client_name' => CLIENT_NAME
+      }
+
+      feature_stack = Thread.current[:gitaly_feature_stack]
+      feature = feature_stack && feature_stack[0]
+      metadata['call_site'] = feature.to_s if feature
+
+      { metadata: metadata }
     end
 
     def self.token(storage)
@@ -137,7 +147,14 @@ module Gitlab
       Gitlab::Metrics.measure(metric_name) do
         # Some migrate calls wrap other migrate calls
         allow_n_plus_1_calls do
-          yield is_enabled
+          feature_stack = Thread.current[:gitaly_feature_stack] ||= []
+          feature_stack.unshift(feature)
+          begin
+            yield is_enabled
+          ensure
+            feature_stack.shift
+            Thread.current[:gitaly_feature_stack] = nil if feature_stack.empty?
+          end
         end
       end
     end