Creating custom Ohai plugins

Ohai is the tool used by a Chef client to find out everything about the node's environment. During a Chef client run, Ohai populates the node object with all the information it found about the node, such as its operating system, hardware, and so on.

It is possible to write custom Ohai plugins to query additional properties about a node's environment.

Tip

Please note that Ohai data isn't populated until after a successful chef-client run!

In this example, we will see how to query the currently active firewall rules with Ohai using iptables and make them available as node attributes.

Getting ready

Make sure you have iptables installed on your node. See the Managing firewalls with iptables recipe in Chapter 7, Servers and Cloud Infrastructure.

Make sure you have the chef-client cookbook available:

1. Add the chef-client cookbook to your Berksfile:

   mma@laptop:~/chef-repo $ subl Berksfile
   cookbook 'chef-client'
   

2. Add the chef-client cookbook to your node's run list:

   mma@laptop...