There are variety of options open to the sysadmin when serving Ruby applications.
One of them is thin. This is a 3rd party web server that is proxied to from the main web server (similar to mongrels in a general setup). Let's take a look at installing thin.
I am assuming you have Ruby and Rubygems installed on your Slice. If you don't, please see the CentOS Ruby on Rails article.
Thin is a rubygem and so installation couldn't be easier:
sudo gem install thin
On the test Slice with a basic rubygems and Rails installation, the process installed the following gems:
rack-0.9.1 eventmachine-0.12.6 daemons-1.0.10 thin-1.0.0
There will be separate articles for proxying to thin from different web servers (Apache, Nginx, etc).
As such, we'll only look at the basics of thin, leaving Virtual Host configurations for later.
To determine the thin verion:
As is often the case in the wacky world of the developer, each version has a unique name:
thin 1.0.0 codename That's What She Said
Starting and stopping
Starting thin requires you to navigate to the rails directory and issue this command:
thin start -d
The '-d' option runs it in the background. If you omitted the '-d' option, it would act in a similar manner to the webbrick server and requires an 'open' terminal. In that case, a standard 'Ctl -C' would kill the process.
In any case the resulting output will be shown as follows:
!! Ruby 1.8.5 is not secure please install cgi_multipart_eof_fix: gem install cgi_multipart_eof_fix
We need to follow the instructions and install a security fix for Ruby v.1.8.5 before thin will run correctly on our slice.
gem install cgi_multipart_eof_fix
Now let's try to start thin again:
thin start -d
To stop thin, you don't need to worry about finding the PID or searching for something to kill:
The default environment for thin is development. To start it in a production environment is easy:
thin start -d -e production
It would be relatively unusual for a Rails application to only need 1 ruby server, so to start a cluster of 3 would require this:
thin start --servers 3
The output shows 3 servers being started sequentially from port 3000 (the default port).
Stopping the cluster is just as easy:
thin stop --servers 3
Again, the output is very clear: a quit signal is sent to each PID.
You can add thin to a runlevel (/etc/init.d/) with ease.
To start with you need to create the script:
sudo thin install
Then add the script to the default runlevels:
sudo /sbin/chkconfig --level 345 thin on
We can check that thin is set to run on the run levels specified by issuing:
sudo /sbin/chkconfig --list thin
The output confirms the process:
thin 0:off 1:off 2:on 3:on 4:on 5:on 6:off
Now we need to define which (if any) of the rails applications to start on a reboot.
Just for example, assume I have a rails application located here:
I want to start 3 thin servers and be in production mode when they are started:
sudo thin config -C /etc/thin/testapp.yml -c /home/demo/public_html/testapp/ --servers 3 -e production
Have a look at the file that was created:
pid: tmp/pids/thin.pid log: log/thin.log timeout: 30 port: 3000 max_conns: 1024 max_persistent_conns: 512 environment: production chdir: /home/demo/public_html/testapp require:  address: 0.0.0.0 servers: 3 daemonize: true
As you can see, there are several options that can be tweaked by hand if needed.
Note the server numbers and environment are exactly as we set them. You can, of course, add as many or as few options to the command as you require, such as port numbers and so on.
When the Slice is rebooted, the 3 thin servers will now start automatically.
As with most applications, there is more than I can go into here but please do check out all the options that are available to you:
Thin is an established method of serving Ruby on Rails applications. I hope this introduction outlines how easy and sysadmin friendly thin actually is.
To see how to proxy to the thin web server from Apache or Nginx, please see the next few articles.