Reconfiguring the whole rails stack via a central YAML file

val — Mon, 20 Aug 2007 02:07:00 +0000

The challenge with hosting of multiple Rails-based Facebook applications is that the amount of users grow quickly. To address this problem we are using EC2 nodes that we can expand/shrink as the demand grows. The price/performance ratio isn’t quite what we first expected, so we are moving toward having a few dedicated boxes instead. Another problem that we add at least a couple of applications a week. On each box that hosts them, we need to reconfigure monit, haproxy, nginx, logrotate and nagios.

To mitigate both issues on dedicated boxes, we resolved to have a central configuration definition in svn with individual box configurations keyed on localhost name. A ruby script regenerates all those aforementioned configuration files from ERB-processed templates when it is run on a box and bounces the services. A sample config looks like:

dedicated-1:

    description: "The dedicated box #1"
    ip: 64.233.167.99
    failover: dedicated-2

    apps:

        bookshelf:
            port: 5000
            instances: 20
            response: Book

        ljconnect:
            port: 6000
            instances: 7
            virtual: ljconnect.hungrymachine.com
            response: Journal

That definition would generate a monit config with 20 instances of the bookshelf application and 7 instances of the ljconnect application plus all other configurations (including nagios health checks expecting the response value) . It is all possible because we adopt a fixed application deployment file structure and port numbering conventions (via offsets) for all servers.

Hungry Machine » yaml

Reconfiguring the whole rails stack via a central YAML file