allowing for graceful unicorn restarts

closes #7217

Changelog.md

@@ -28,6 +28,7 @@
 * Update notifications every 5 minutes and when opening the notification dropdown [#6952](https://github.com/diaspora/diaspora/pull/6952)
 * Show browser notifications when receiving new unread notifications [#6952](https://github.com/diaspora/diaspora/pull/6952)
 * Only clear comment textarea when comment submission was successful [#7186](https://github.com/diaspora/diaspora/pull/7186)
+* Add support for graceful unicorn restarts [#7217](https://github.com/diaspora/diaspora/pull/7217)
 
 # 0.6.1.0
 

config/defaults.yml

@@ -42,7 +42,7 @@ defaults:
   server:
     listen: '0.0.0.0:3000'
     rails_environment: 'development'
-    pid:
+    pid: "tmp/pids/web.pid"
     stderr_log:
     stdout_log:
     unicorn_worker: 2

config/diaspora.yml.example

@@ -177,8 +177,8 @@ configuration: ## Section
     #listen: 'unix:/run/diaspora/diaspora.sock'
     #listen: '127.0.0.1:3000'
 
-    ## Set the path for the PID file of the unicorn master process (default=none)
-    #pid: '/run/diaspora/diaspora.pid'
+    ## Set the path for the PID file of the unicorn master process (default=tmp/pids/web.pid)
+    #pid: 'tmp/pids/web.pid'
 
     ## Rails environment (default='development').
     ## The environment in which the server should be started by default.

config/eye.rb

@@ -12,10 +12,21 @@ Eye.application("diaspora") do
   stderr "log/eye_processes_stderr.log"
 
   process :web do
-    start_command "bin/bundle exec unicorn -c config/unicorn.rb"
-    daemonize true
-    pid_file "tmp/pids/web.pid"
+    unicorn_command = "bin/bundle exec unicorn -c config/unicorn.rb"
+
+    if rails_env == "production"
+      start_command "#{unicorn_command} -D"
+      daemonize false
+      restart_command "kill -USR2 {PID}"
+      restart_grace 10.seconds
+    else
+      start_command unicorn_command
+      daemonize true
+    end
+
+    pid_file AppConfig.server.pid.get
     stop_signals [:TERM, 10.seconds]
+
     env "PORT" => ENV["PORT"]
 
     monitor_children do

config/unicorn.rb

@@ -4,7 +4,7 @@ port = ENV["PORT"]
 port = port && !port.empty? ? port.to_i : nil
 
 listen port || AppConfig.server.listen.get unless RACKUP[:set_listener]
-pid AppConfig.server.pid.get if AppConfig.server.pid?
+pid AppConfig.server.pid.get
 worker_processes AppConfig.server.unicorn_worker.to_i
 timeout AppConfig.server.unicorn_timeout.to_i
 stderr_path AppConfig.server.stderr_log.get if AppConfig.server.stderr_log?
@@ -26,11 +26,25 @@ before_fork do |_server, _worker|
   end
 end
 
-after_fork do |_server, _worker|
+after_fork do |server, worker|
   Logging.reopen # reopen logfiles to obtain a new file descriptor
 
   ActiveRecord::Base.establish_connection # preloading app in master, so reconnect to DB
 
   # We don't generate uuids in the frontend, but let's be on the safe side
   UUID.generator.next_sequence
+
+  # Check for an old master process from a graceful restart
+  old_pid = "#{AppConfig.server.pid.get}.oldbin"
+
+  if File.exist?(old_pid) && server.pid != old_pid
+    begin
+      # Remove a worker from the old master when we fork a new one (TTOU)
+      # Except for the last worker forked by this server, which kills the old master (QUIT)
+      signal = (worker.nr + 1) >= server.worker_processes ? :QUIT : :TTOU
+      Process.kill(signal, File.read(old_pid).to_i)
+    rescue Errno::ENOENT, Errno::ESRCH
+      # someone else did our job for us
+    end
+  end
 end