Merge branch 'sh-make-unicorn-work-rbtrace' into 'master'

Make rbtrace work under unicorn

See merge request gitlab-org/gitlab-ce!20892

config/initializers/rbtrace.rb

-# frozen_string_literal: true
-
-require 'rbtrace' if ENV['ENABLE_RBTRACE']

config/initializers/sidekiq.rb

@@ -8,6 +8,8 @@ Sidekiq.default_worker_options = { retry: 3 }
 enable_json_logs = Gitlab.config.sidekiq.log_format == 'json'
 
 Sidekiq.configure_server do |config|
+  require 'rbtrace' if ENV['ENABLE_RBTRACE']
+
   config.redis = queues_config_hash
 
   config.server_middleware do |chain|

config/unicorn.rb.example

@@ -124,6 +124,10 @@ before_fork do |server, worker|
 end
 
 after_fork do |server, worker|
+  # Unicorn clears out signals before it forks, so rbtrace won't work
+  # unless it is enabled after the fork.
+  require 'rbtrace' if ENV['ENABLE_RBTRACE']
+
   # per-process listener ports for debugging/admin/migrations
   # addr = "127.0.0.1:#{9293 + worker.nr}"
   # server.listen(addr, :tries => -1, :delay => 5, :tcp_nopush => true)

doc/administration/troubleshooting/debug.md

@@ -77,7 +77,12 @@ and more. However, this is not enabled by default. To enable it, define the
 gitlab_rails['env'] = {"ENABLE_RBTRACE" => "1"}
 ```
 
-Then reconfigure the system and restart Unicorn and Sidekiq.
+Then reconfigure the system and restart Unicorn and Sidekiq. To run this
+in Omnibus, run as root:
+
+```ruby
+/opt/gitlab/embedded/bin/ruby /opt/gitlab/embedded/bin/rbtrace
+```
 
 ## Common Problems