Mongrel Cluster a quick note - and extra notes

A few quick notes concerning Mongrel load balancing setup behind an Apache proxy server. These are a few gotcha's I encountered that should be shared with the rest of the webosphere (hopefully if you have the same problem you'll be directed here for a quick bit of help).

First, I am assuming the following: You have apache2 up and running, and you are trying to proxy requests to mongrel_rails - which you have at least one server running...

If you receive an Apache error stating that you do not have permission to access a particular directory (which normally you do, except when you try to proxy).. and you see in the apache2/error.log

Or something similar... then you need to do the following. Edit apache's proxy.conf which is nicely configured right off the bat to be a pain in the butt:

Inside you will see something like the following - make yours match this - all I did was comment out the "Deny from all" and add an "Allow from 127.0.0.1" -- this assumes that you are only proxying on the localhost.

Next lets cover a quick tutorial (more for my benefit than anything else) on exactly how do you setup the mongrel cluster. These are very specific instructions for Ubuntu - sorry I dont have the time to expand these to be very thorough or general, again I assume you already have mongrel_rails in place and working (see my previous post for a gotcha there).

Also - I put a blank line in between shell commands. If there isn't a blank line between something then consider it all to be on one line when you type it into the shell console.

Im also basing this off a particular setup that was quite different from one I had dealt with before - so be warned this may not match exactly what you have.

There you just installed mongrel_cluster then took added the mongrel_cluster command to your init folder - and prepared it for on-bootup execution. Now if you look inside the mongrel_cluster file:

You will see this line:

If you try to run mongrel_cluster at this point (or at least on my system) -

Thats why you will also need to do this:

Good, almost there - now create a directory in /etc called "mongrel_cluster" (This is the Required name!!!)

Now, go into your rails project directory (so that if you were to type ls you would see the app/ config/ log/ public/ etc... folders). Then create your mongrel_cluster config:

This will update the file config/mongrel_cluster.yml in your rails app. You can test it by doing "sudo mongrel_rails cluster::start" -- check that it correctly created your pid files inside the log/ directory - then do a "sudo mongrel_rails cluster::stop".

Now, link that config into your mongrel_cluster directory:

Finally setup the server to autostart the mongrel_cluster upon reboot:

So, now your mongrel cluster should boot up and dazzle you with its ease of setup. So - lets take a big look at that VirtualHost setup in your apache config - how, now, do you configure your VHost to support multiple mongrel servers? Not too hard, here is what you will need inside your VHost config to make it properly proxy requests to Mongrel.

Well, I lied.. I thought this would be a quick post - but it wasn't. I guess it doesn't matter, I wont loose any sleep over it.

Until next time, happy coding =)