Ohai is the tool used by a Chef client to find out everything about the node's environment. During a Chef client run, Ohai plugin 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.
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 using iptables and make them available as node attributes.
Make sure you have
iptables installed on your node. See the Managing firewalls with iptables recipe in Chapter 7, Servers and Cloud ...