How to setup a full blown Mongrel Cluster powered Rails app on a CentOS server with Pound Load Balancing
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Author: Alexandru Ungur and Robert Eaton

This little guide, outlines all the steps needed to bootstrap a full blown
Mongrel cluster powered Rails install on a brand new CentOS 4.x box. We cover all of the sofware needed as well the steps needed to actually get
it installed and configured. Following the best practices in the business,
wherever possible, the packages from standard CentOS were used, except for
situations where it came into conflict with Rails own requirements (Ruby
1.8.1 that comes with CentOS is a little too old for Rails).

Here we go:

PART I - Setting up a blank CentOS box for Rails
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==Server Set Up==

We will not go into this too deeply, but… a suggestion would be to install your unix server with a fresh install of CENTOS 4.4 without Cpanel or Plesk.

(This is what was used during the writting of this article, things may have changed since this article was written, if this article has some time against it, I suggest doing some research to see what has changed.)

CPanel has a bad habit of rewritting the apache config file which will destroy everything we are doing. Cpanel also comes with a different version of Apache than what we need. Plesk is a wonderful server admin tool, but it also conflicts with what we are doing. We suggest provisioning your server with CENTOS 4 (4.4 actually) without a control panel of any kind. Since the actual job this article was created for used a Godaddy Dedicate Unix Server. We will explain how to do this using Godaddy Servers.

==Which server to get?==

We started with a Godaddy Dedicated Unix Server. Nothing special. Just a Centos box will do! We upgraded ours with a Pentium 4 and selected the NO CONTROL PANEL OPTION. (This was actually Robert’s 3rd attempt… 1st time with plesk, second time with Cpanel, third time… NO STINKING PANEL!) Learn from my mistakes… do it right the first time and you will save 5 yourself a 5 day battle against those controlling control panels! The beautiful part about installing without a control panel with a Godaddy Centos 4 box is when you install without these panels, you get the Apache 2.0 Server with the default Centos 4.4. If you install Cpanel, we ended up with Apache 1.3! It is best to use a Centos Operating system that uses the needed services by default than to custom compile apache, the reason is because these packages are tested by many contributors in the Centos Project for bugs and security issues. When you custom compile a service like apache, you risk messing up a lot of work many people have already optimized! Unless your a guru, then I will leave that decesion up to you!
Once your server is ready… log into ssh and switch to root user.

== Exim ==

Exim is a powerfull MTA which is an excellent alternative to Sendmail. Comes by
default with CentOS and requires no setup at all to get it started on CentOS.
Just install and start it:

(make sure you remove sendmail first if it is installed)

up2date exim
service exim start
chkconfig exim on

== Subversion ==

Subversion instal consits of two parts. Installing the software and setting up
the network access to the repositories. Please refer to the documentation for the
full explanations of the format of the svnserve.conf file, but for a basic install,
disabling anonymous access and granting read/write rights to authenticated users
is usually enough.

up2date subversion
svnadmin create /var/svn
(edit /var/svn/conf/svnserve.conf, setup access)
(edit /var/svn/conf/passwd to setup users/password)
svnserve -d -r /var/svn
(add the above command to /etc/rc.d/rc.local)

== MySQL Server ==

Thanks to the excellent yum installer, the MySQL server install is a snap on any
RHEL/CentOS box:

yum groupinstall “MySQL Database”
yum install mysql-server
service mysqld start
chkconfig mysqld on

== Apache webserver ==

Once again, nothing amazing. We install the standard httpd package from CentOS,
which at the time of writting this is apache 2.0.5x

up2date httpd
(edit /etc/httpd/conf/httpd.conf to suit your needs, in our case that simply
means configuring a virtual host to proxy the requests to the balancer[1])
service httpd start
chkconfig httpd on

== Install Ruby and Rubygems software ==

These are the only packages that will be compiled from source on this guide. Due
to the fact that the versions that ship with CentOS4.4 are obsolete for Rails, we
will have to compile these from source:

wget http://ftp.ruby-lang.org/pub/ruby/1.8/ruby-1.8.5-p2.tar.gz
tar xzf ruby*tar.gz && rm -f ruby*tar.gz
cd ruby*; ./configure && make && make install
cd ..; rm -rf ruby*

wget http://rubyforge.org/frs/download.php/20585/rubygems-0.9.3.tgz
tar xzf rubygems*tgz && rm -f rubygems*tgz
cd rubygems*; ruby setup.rb
cd ..; rm -rf rubygems*

== Install Ruby gems ==

Install the necessary Ruby gems for the application to start up and work

gem install -r rails –include-dependencies
gem install -r mongrel –include-dependencies
gem install -r mongrel_cluster –include-dependencies
gem install -r capistrano –include-dependencies

== Install Pound HTTP balancer ==

Although this is not available in CentOS either, we install this from the excellent
and worthtrusty Dag repository, in .rpm format. It’s one step better than compilling
things by hand, and the best step when packages are not available in CentOS by default

(available at: http://dag.wieers.com/rpm/packages/pound/)
wget http://dag.wieers.com/rpm/packages/pound/pound-2.3-1.el4.rf.i386.rpm
rpm -ivh pound*rpm && rm -f pound*rpm
(edit /etc/pound.cfg)
(pound # delay its start until you start the mongrel cluster first)
(add it to /etc/rc.d/rc.local)

== Fetch the Rails application ==

Typically the application is checked out from a VCS repository (subversion in this
guide) the DB access setup, and the mongrel cluster config file installed. Then
we’re ready to go

(svn co <repo>; cd app)
(install the mongrel cluster config file[3]: config/mongrel_cluster.yml)
mongrel_rails cluster::start

== Done ==

Point your browser to the domainname you configured for this Rails app and enjoy!
It should all be up & running at this point.

PART II - Adding additional Rails apps on an already configured box
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Ok, if you followed the first part of the tutorial, you should have a Rails enabled
CentOS box at this point. Now how to add aditional application… ? Quite easy
All the software is already in place, which means we only need to add a couple of
configurations and we should be done. Here are the steps:

1. configure a new virtual host for the additional domain
2. configure an additional balancer for the new cluster
3. setup a new cluster for the new Rails app

So in other words, each app, gets it’s own independent cluster, which in turn requires
it’s own balancer, which in turn requires it’s own domain that will be proxied from an
Apache virtual host.

For step 1, simply use the attached config file[1] as a template, and set it up for
the new domain. What you do need to change, besides the domainname of course, is the
port you will redirect to. That port is the same port pound will listen on. So, suppose
the first application uses port 82 like in the sample config file, then for an additional
app you would use the next port, say 83. Then what you need to do is this:

1. create a new virtual host using port 83 to proxy the requests to, or whatever port you wan, we are using port 83 in this example.

2. Then create an additional pound config file, you could name it /etc/pound2.cfg

Use for this one the pound config template[2] but modify the port it listens to
from 82 to 83. Now the new apache virtual host will correctly proxy the requests
to the new pound balancer, which is configured properly to listen on a new port.
There’s one more step now needed for pound:
Change the ports for the cluster. In the template we use ports 8000 to 8003
for the four mongrels that are part of the first cluster, so we need now another
four ports. Simply pick the next four, 8004 to 8007 and replace them accordingly
in the new pound config file. That’s it for pound. Now it knows to listen on the
new port and to forward the requests to the new ports. Let’s setup a new mongrel
cluster now.

3. Use the template[3] and copy it in the config folder of the new Rails app we’re
setting up right now. Edit the first line to start from 8004 instead of 8000
and that’s it for Mongrel.

Now, with all the files in place, we’re ready to start it all.
1. cd to the root of the new Rails app and issue:

mongrel_rails cluster::start

2. run this to start the balancer:

pound -f /etc/pound2.cfg

3. and this to restart apache

service httpd restart

Enjoy it!
Your new Rails app, should be up and running now

Sample config files used in this guide
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[1] Sample apache setup for proxying requests to a balancer

<VirtualHost *:80>
ServerName ruby.cookbookwiki.com
ProxyPass / http://127.0.0.1:82/
ProxyPassReverse / http://127.0.0.1:82
ProxyPreserveHost on
</VirtualHost>

[2] Simple pound configuration for a cluster with 4 mongrels

ListenHTTP
Address 0.0.0.0
Port 82
Service
BackEnd
Address 127.0.0.1
Port 8000
End
BackEnd
Address 127.0.0.1
Port 8001
End
BackEnd
Address 127.0.0.1
Port 8002
End
BackEnd
Address 127.0.0.1
Port 8003
End
End
End

[3] Sample 4 mongrel clusters config file

port: 8000
pid_file: /tmp/test-mongrel.pid
servers: 4
address: 127.0.0.1
environment: development