Use unicorn in Docker container

config/unicorn.rb

@@ -0,0 +1,55 @@
+ASCIINEMA_HOME = ENV["ASCIINEMA_HOME"] || Dir.pwd
+UNICORN_WORKERS = (ENV["UNICORN_WORKERS"] || "4").to_i
+
+# Use at least one worker per core if you're on a dedicated server,
+# more will usually help for _short_ waits on databases/caches.
+worker_processes UNICORN_WORKERS
+
+# Help ensure your application will always spawn in the symlinked
+# "current" directory that Capistrano sets up.
+working_directory ASCIINEMA_HOME
+
+listen 3000, :tcp_nopush => true
+
+# nuke workers after 60 seconds
+timeout 60
+
+# feel free to point this anywhere accessible on the filesystem
+pid "#{ASCIINEMA_HOME}/tmp/unicorn.pid"
+
+preload_app true
+
+# Enable this flag to have unicorn test client connections by writing the
+# beginning of the HTTP headers before calling the application.  This
+# prevents calling the application for connections that have disconnected
+# while queued.  This is only guaranteed to detect clients on the same
+# host unicorn runs on, and unlikely to detect disconnects even on a
+# fast LAN.
+check_client_connection false
+
+before_exec do |server|
+  ENV["BUNDLE_GEMFILE"] = "#{ASCIINEMA_HOME}/Gemfile"
+end
+
+before_fork do |server, worker|
+  if defined?(ActiveRecord::Base)
+    ActiveRecord::Base.connection.disconnect!
+    Rails.logger.info('Disconnected from ActiveRecord')
+  end
+
+  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
+    end
+  end
+end
+
+after_fork do |server, worker|
+  if defined?(ActiveRecord::Base)
+    ActiveRecord::Base.establish_connection
+    Rails.logger.info('Connected to ActiveRecord')
+  end
+end

docker/supervisor/asciinema.conf

@@ -6,6 +6,6 @@ command=/usr/sbin/nginx -g "daemon off;"
 redirect_stderr=true
 
 [program:rails]
-command=bundle exec rails server
+command=bundle exec unicorn -p 3000 -c config/unicorn.rb
 redirect_stderr=true
 directory=/app