Getting the interface that matches an IP in Puppet

I was recently in a situation where I needed to figure out which interface name matched a particular, static IPv4 address. On a single or a handful of nodes this could have been hardcoded in Hiera, for example, but there were dozens of nodes. The way I solved this was by creating a custom fact that uses the IPv4 address and loops through the interfaces list to find the matching interface name:

# frozen_string_literal: true

Get the name of the interface that is bound to 192.168.122.10

Facter.add(:kvm_iface) do

confine kernel: ‘Linux’

desired_ip = ‘192.168.122.10’ interfaces_fact = Facter.value(:networking)[‘interfaces’] interfaces_list = interfaces_fact.keys interfaces_list.each do |interface| interface_ip = interfaces_fact[interface][‘bindings’][0][‘address’] next unless interface_ip == desired_ip

`desired_interface = interface`
`setcode do`
  `desired_interface`
`end`

end end

In the end the code did not get used because we could rely on the interface name being static, but hopefully this code is helpful for somebody else.