unicorn / rails的零停机时间重启

Question

在我们的部署脚本中，我们使用以下代码段重新启动unicorn：

desc "Zero downtime restart of Unicorn"
task :restart do
  run "kill -s USR2 unicorn_pid"
end

主进程分叉，启动新工作人员然后杀死旧工作人员。但现在似乎新主人杀死了旧主人，并在新孩子完全开始之前接管任何新连接。当我们使用preload_app false禁用应用程序的预加载时，新工作人员需要大约30到60秒才能启动。在此期间，新连接/网站挂起。如何避免这种情况，以便新主人只有在新孩子完全准备好并准备服务器请求后才接管？ ：）

更新

我的unicorn.rb看起来像这样：

# name of application
application = "myapp"

# environment specific stuff
case ENV["RAILS_ENV"]
when "integration", "staging"
  worker_processes 1
when "production"
  worker_processes 4
else
  raise "Invalid runtime environment '#{ENV["RAILS_ENV"]}'"
end

# set directories
base_dir = "/srv/#{application}/current"
shared_path = "/srv/#{application}/shared"
working_directory base_dir

# maximum runtime of requests
timeout 300

# multiple listen directives are allowed
listen "#{shared_path}/unicorn.sock", :backlog => 64

# location of pid file
pid "#{shared_path}/pids/unicorn.pid"

# location of log files
stdout_path "#{shared_path}/log/unicorn.log"
stderr_path "#{shared_path}/log/unicorn.err"

# combine REE with "preload_app true" for memory savings
# http://rubyenterpriseedition.com/faq.html#adapt_apps_for_cow
preload_app false
if GC.respond_to?(:copy_on_write_friendly=)
  GC.copy_on_write_friendly = true
end

before_exec do |server|
  # see http://unicorn.bogomips.org/Sandbox.html
  ENV["BUNDLE_GEMFILE"] = "#{base_dir}/Gemfile"
end

before_fork do |server, worker|
  # the following is highly recomended for "preload_app true"
  if defined?(ActiveRecord::Base)
    ActiveRecord::Base.connection.disconnect!
  end
  if defined?(Sequel::Model)
    Sequel::DATABASES.each{ |db| db.disconnect }
  end

  # This allows a new master process to incrementally
  # phase out the old master process with SIGTTOU to avoid a
  # thundering herd (especially in the "preload_app false" case)
  # when doing a transparent upgrade. The last worker spawned
  # will then kill off the old master process with a SIGQUIT.
  old_pid = "#{server.config[:pid]}.oldbin"
  if old_pid != server.pid
    begin
      sig = (worker.nr + 1) >= server.worker_processes ? :QUIT : :TTOU
      Process.kill(sig, File.read(old_pid).to_i)
    rescue Errno::ENOENT, Errno::ESRCH
      # someone else did our job for us
    end
  end
end

after_fork do |server, worker|
  if defined?(ActiveRecord::Base)
    ActiveRecord::Base.establish_connection
  end
end

我认为主要问题是没有child_ready钩子。 before_fork和after_hook被称为“太早”。我想我可以在after_fork钩子中添加一些逻辑来以某种方式检测孩子何时准备好...但我希望有一个更简单的解决方案？ ：）