Using Augeas to reliably edit config files

Sometimes it seems like every application has its own subtly different config file format, and writing regular expressions to parse and modify all of them can be a tiresome business.

Thankfully, Augeas is here to help. Augeas is a system that aims to simplify working with different config file formats by presenting them all as a simple tree of values. Puppet's Augeas support allows you to create augeas resources that can make the required config changes intelligently and automatically.

How to do it...

Follow these steps to create an example Augeas resource:

1. Modify your base module as follows:

class base {
  augeas { 'enable-ip-forwarding':
    incl    => '/etc/sysctl.conf',
    lens    => 'Sysctl.lns',
    changes => ['set net.ipv4.ip_forward 1'],
  }
}

2. Run Puppet:

[root@cookbook ~]# puppet agent -t
Info: Using configured environment 'production'
Info: Retrieving pluginfacts
Info: Retrieving plugin
Info: Caching catalog for cookbook.example.com...