Starting or Restarting Unicorn with Capistrano 3.X

Starting or restarting Unicorn with Capistrano 3.x

Can't say anything specific about capistrano 3(i use 2), but i think this may help: How to run shell commands on server in Capistrano v3?.
Also i can share some unicorn-related experience, hope this helps.

I assume you want 24/7 graceful restart approach.

Let's consult unicorn documentation for this matter. For graceful restart(without downtime) you can use two strategies:

1. kill -HUP unicorn_master_pid It requires your app to have 'preload_app' directive disabled, increasing starting time of every one of unicorn workers. If you can live with that - go on, it's your call.

2. kill -USR2 unicorn_master_pid
kill -QUIT unicorn_master_pid

More sophisticated approach, when you're already dealing with performance concerns. Basically it will reexecute unicorn master process, then you should kill it's predecessor. Theoretically you can deal with usr2-sleep-quit approach. Another(and the right one, i may say) way is to use unicorn before_fork hook, it will be executed, when new master process will be spawned and will try to for new children for itself.
You can put something like this in config/unicorn.rb:

# Where to drop a pidfile
pid project_home + '/tmp/pids/unicorn.pid'

before_fork do |server, worker|
  server.logger.info("worker=#{worker.nr} spawning in #{Dir.pwd}")

  # graceful shutdown.
  old_pid_file = project_home + '/tmp/pids/unicorn.pid.oldbin'
  if File.exists?(old_pid_file) && server.pid != old_pid_file
    begin
      old_pid = File.read(old_pid_file).to_i
      server.logger.info("sending QUIT to #{old_pid}")
      # we're killing old unicorn master right there
      Process.kill("QUIT", old_pid)
    rescue Errno::ENOENT, Errno::ESRCH
      # someone else did our job for us
    end
  end
end

It's more or less safe to kill old unicorn when the new one is ready to fork workers. You won't get any downtime that way and old unicorn will wait for it's workers to finish.

And one more thing - you may want to put it under runit or init supervision. That way your capistrano tasks will be as simple as sv reload unicorn, restart unicorn or /etc/init.d/unicorn restart. This is good thing.

How to make capistrano 3 run rake and start unicorn?

you can do something like this:

%w[start stop restart].each do |command|
desc "#{command} unicorn server"
  task command, roles: :app, except: {no_release: true} do
    run "/etc/init.d/unicorn_#{application} #{command}"
  end
end

and regard your task:

task :your_task, :roles => :app do
  run "cd #{release_path}; bundle exec rake db:production RAILS_ENV=#{rails_env}"
end

Unicorn restart issue with capistrano

You should set the BUNDLE_GEMFILE environment variable before you start the server, point it at current/Gemfile.

Unicorn restart issue when deploying my rails app (capistrano)

I had the similar issue, what helped was to put

listen 3000, reuseport: true

reuseport: true to my unicorn.rb

Capistrano-unicorn gem getting wrong environment set

Ok, after a long time not having the correct environment, I have discovered the issue!

Basically, my init scripts were running BEFORE my capistrano-unicorn bin was doing its thing.

So, make sure that your init.d or upstart scripts to manage Unicorn and its workers are taken into account when capistrano-unicorn is doing the unicorn restart / reload / duplication tasks.

I did not think to look at these scripts when I had to debug the stale pid file / already running / unable to listen on socket errors. But it makes sense, as upstart starts Unicorn when it is not running, and then capistrano-unicorn is also attempting to start Unicorn.

I have now combined these capistrano tasks and hooks with Monit and a Unicorn init script.

Capistrano tasks:

namespace :monit do
  desc ' wait 20 seconds '
  task :wait_20_seconds do
    sleep 20
  end
  task :monitor_all, :roles => :app do
    sudo "monit monitor all"
  end

  task :unmonitor_all, :roles => :app do
    sudo "monit unmonitor all"
  end

  desc 'monitor unicorn in the monit rc file'
  task :monitor_unicorn, :roles => :app do
    sudo "monit monitor unicorn"
  end

  desc 'unmonitor unicorn in the monit rc file'
  task :unmonitor_unicorn, :roles => :app do
    sudo "monit unmonitor unicorn"
  end
end

Capistrano hooks:

after 'deploy:restart', 'unicorn:duplicate'  # app preloaded. check https://github.com/sosedoff/capistrano-unicorn section for zero downtime

before 'deploy', "monit:unmonitor_unicorn"
before 'deploy:migrations', "monit:unmonitor_unicorn"

after 'deploy', 'monit:wait_20_seconds'
after "deploy:migrations", "monit:wait_20_seconds"

after 'monit:wait_20_seconds', 'monit:monitor_unicorn'

I use Monit to monitor my unicorn process:

Within /etc/monit/monitrc:

check process unicorn
  with pidfile /var/www/apps/my_app/shared/pids/mypid.pid
  start program = "/usr/bin/sudo service unicorn start"
  stop program = "/usr/bin/sudo service unicorn stop"

Within your init script, you will start the unicorn process with something like:
unicorn_rails -c /var/www/apps/my_app/current/config/unicorn.rb -E staging -D
Make sure the -E flag is set to the correct environment. The capistrano-unicorn gem has directives using :set within deploy.rb which allow you to specify the environment for that unicorn process.

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