Starting background tasks with Capistrano - ruby-on-rails

Question

For my RubyOnRails-App I have to start a background job at the end of Capistrano deployment. For this, I tried the following in deploy.rb:
run "nohup #{current_path}/script/runner -e production 'Scheduler.start' &", :pty => true
Sometimes this works, but most of the time it does not start the process (= not listed in ps -aux). And there are no error messages. And there is no nohup.out, not in the home directory and not in the rails app directory.
I tried using trap('SIGHUP', 'IGNORE') in scheduler.rb instead of nohup, but the result is the same.
The only way to get it work is removing the ":pty => true" and do a manual Ctrl-C at the end of "cap deploy". But I don't like this...
Are there any other chances to invoke this Scheduler.start? Or to get some more error messages?
I'm using Rails 2.3.2, Capistrano 2.5.8, Ubuntu Hardy on the Server

Answer 1

With :pty => true, user shell start-up scripts (e.g. bashrc, etc.) are (usually) not loaded. My ruby program exited right after launching because of the lack of dependent environment variables.
Without :pty => true, as you described in the question, capistrano hangs there waiting for the process to exit. You'll need to redirect both stdout and stderr to make it return immediately.
run 'nohup ruby -e "sleep 5" &' # hangs for 5 seconds
run 'nohup ruby -e "sleep 5" > /dev/null &' # hangs for 5 seconds
run 'nohup ruby -e "sleep 5" > /dev/null 2>&1 &' # returns immediately. good.
If your background task still doesn't run. Try redirecting stdout and stderr to a log file so that you can investigate the output.

Answer 2

I'd like to share my solution which also works when executing multiple commands. I tried many other variants found online, including the "sleep N" hack.
run("nohup sh -c 'cd #{release_path} && bundle exec rake task_namespace:task_name RAILS_ENV=production > ~/shared/log/<rakelog>.log &' > /dev/null 2>&1", :pty => true)
This is a dup response launching background process in capistrano task but want to make sure others and myself can google for this solution.

Answer 3

Do you want your Scheduler job to run continually in the background and get restarted when you run Capistrano?
If so, then for that I use runit http://smarden.sunsite.dk/runit/ and DelayedJob http://github.com/Shopify/delayed_job/tree/master
Install runit in the mode of not replacing init
Add your background job as a runit service and add the log monitor for it from runit.
Have Capistrano call sudo sv kill job_name to kill and restart the job.
My backround job is an instance of the Rails plugin DelayedJob which handles background Rails tasks. I kill it with every Capistrano deploy so it will restart with the updated code base.
This has proved to be very reliable.
HTH,
Larry

Answer 4

If this task scheduler has a -d switch it will work. For example passenger standalone has a -d option to start it as a demonized process.
namespace :passenger_standalone do
task :start do
run "cd #{current_path} && passenger start -e #{rails_env} -d"
end
task :stop do
run "cd #{current_path} && RAILS_ENV=#{rails_env} passenger stop"
end
task :restart do
stop
start
end
end