How to implement auto starting and exiting daemons in rails

Question

I'm a bit overwhelmed by mere amount a possible solutions the Rails community has created for my problem. So perhaps anyone can help me to figure out how to solve it best.

What I want to do is to write a Rails app that behaves kind of "dropbox". On the one hand it should be a web interface where I can upload and download files to my web server. This interacts with my database and all that stuff. On the other hand I have SSH access to that server and can put files there manually. Now I want this file system actions to trigger my Rails app to do the things it would do if I'd created the file via the web interface.

So I somehow write a daemon, right? There are a lot of solutions, like
daemons.rubyforge.org/
github.com/mirasrael/daemons-rails
github.com/costan/daemonz
github.com/kennethkalmer/daemon-kit

Another feature that I would like to have, is that my Rails app automatically spawns and stops my daemon as start or quit my Rails app resp. So "daemonz" seems the best solution. But as I googled further I found
github.com/FooBarWidget/daemon_controller/
which seems a lot more "high tech" and already used as I deploy with passenger. But I don't understand if it kills my daemons as I quit Rails. I suppose that is not the case and so I wonder how to implement this in my app.

The way to implement a "thing" to react to file system changes seems straight forward for me. I'd use
github.com/guard/listen/
(an alternative would be: github.com/ttilley/fssm )
But what I don't understand as this the first time I'm really faced with this protocol things is, if this spawns a server I'm able to communicate with or what kind of object I have to deal with.

The last thing, I would like to implement is a kind of worker queue so that the listening for file system changes is seperated from the the actions of my rails app. But there are so many solutions that I'm totally overwhelmed to pick one:
github.com/tobi/delayed_job/
github.com/defunkt/resque
http://backgroundrb.rubyforge.org/

And what is
http://godrb.com/
all about? How could that help me?

Has anyone hints how to solve this? Thanks a lot!

Jan

P.S. I'd like to post links to all the github projects but unfortunately I don't have enough 'reputation'

Answer 1

I'd definitely look into creating a process (daemon) that monitors the relevant directory. Then your Rails app can just put files into it without having to know anything about the back end, and it'll work with SSH too.

Your daemon can load the Rails environment & communicate with your database. I'd leave all the communication between them at that level.

As for making it start/stop with your rails app...are you sure? I use god (the ruby gem) to start/monitor processes. It will "daemonize" your Ruby app for you, too. If you want to, you can actually tell god to stop your directory-monitor process & then exit when Rails stops. And you can fire off god from a Rails initializer.

However, if you might find yourself using SSH or some other means to put files into that directory when rails is not running, you might look into putting a script into /etc/init.d to automatically start god when the server boots up.

HTH

Answer 2

I think you want something like Guard for monitoring the changes on the filesystem and performing actions when changes occur.

As for god, you should definitely look into it. It will make starting/stopping processes you depend on considerably easier. We used Bluepill for a while, but there are so many bugs, we ditched it and moved to God, which IMHO is a lot more pleasant to work with, for the mostpart.

Answer 3

Have you tried creating a script file eg:

startDaemon.rb

And then placing it:

config/initializers/ 

?