我是否正确地在Heroku + Unicorn中预加载应用程序？

Question

在Heroku上使用Unicorn时.扩展,将会有问题,因为当它仍然加载应用程序时,请求可以访问新缩放的web dyno.这主要导致超时错误.

我在http://codelevy.com/2010/02/09/getting-started-with-unicorn.html和https://github.com/blog/517-unicorn上做了一些阅读

这两篇文章建议使用preload_app true.和after_fork和before_fork块.

在Rails 3+中,before_block仍然需要代码吗？我读到了某个地方,否则.任何经历过这种情况并且想要分享的人？

我错过了什么吗？我是否正确加载了应用程序？

# config/initializers/unicorn.rb
# Read from:
# http://michaelvanrooijen.com/articles/2011/06/01-more-concurrency-on-a-single-heroku-dyno-with-the-new-celadon-cedar-stack/
worker_processes 3 # amount of unicorn workers to spin up
timeout 30         # restarts workers that hang for 90 seconds

# Noted from http://codelevy.com/2010/02/09/getting-started-with-unicorn.html
# and https://github.com/blog/517-unicorn
preload_app true

after_fork do |server, worker|
  ActiveRecord::Base.establish_connection
end

before_fork do |server, worker|
  ##
  # When sent a USR2, Unicorn will suffix its pidfile with .oldbin and
  # immediately start loading up a new version of itself (loaded with a new
  # version of our app). When this new Unicorn is completely loaded
  # it will begin spawning workers. The first worker spawned will check to
  # see if an .oldbin pidfile exists. If so, this means we've just booted up
  # a new Unicorn and need to tell the old one that it can now die. To do so
  # we send it a QUIT.
  #
  # Using this method we get 0 downtime deploys.

  old_pid = Rails.root + '/tmp/pids/unicorn.pid.oldbin'
  if File.exists?(old_pid) && server.pid != old_pid
    begin
      Process.kill("QUIT", File.read(old_pid).to_i)
    rescue Errno::ENOENT, Errno::ESRCH
      # someone else did our job for us
    end
  end
end

Answer 1

您在这里看到的内容是预期的。当您通过 dyno 进行扩展时，Heroku 平台会将该 slug 部署到新的 dyno，该新的 dyno 与您的其他 dyno（即另一个独角兽大师）完全隔离。

一旦该 dyno 部署并运行（有效启动），路由网格将开始向该 dyno 发送请求，此时 Rails 将在 Unicorn 或您已设置的任何服务器上启动。

但是，一旦请求到达，您就有 30 秒的时间返回数据，否则请求将在路由网格上超时（错误 H12）。

因此，总而言之，您的问题与分叉无关，而是您的应用程序无法在 30 秒内启动，因此会提前超时。在 Heroku 平台上，您无需担心分叉和 PID 文件。