Getting IP Addresses with Facter

When configuring services with Puppet, you sometimes need to know the IP address of a server. For example, I export nagios host definitions from many of my servers and use them to configure my nagios service. Facter ships with two sets of network-related facts that can help.

The first is the ipaddress fact. This fact contains the IP address of the first first network interface reported by ifconfig, which outputs them in alphabetical order. The second is a fact for each network interface that has an IP address; unsurprisingly, it contains the interface's IP address.

For example, here are the facts from a server with three network interfaces, eth0, eth1, and eth2. eth1 and eth2 are bonded as the device bond0.

ipaddress => 172.16.32.48
ipaddress_bond0 => 172.16.32.48
ipaddress_eth0 => 192.0.32.10

In my environment, the device specific facts are too narrow. Although I'm consistent on which interfaces are plugged into which network, some servers use bonding or bridging so I can't assume that the device that has the physical link is what the ip address is assigned to. The private ip might be on eth1 or bond0, for example. Of course, this means the ipaddress fact is too broad. It will be a public IP address on some servers and a private IP address on others, depending on how the interfaces are named.

To improve on this, I've created two custom facts, ipaddress_public and ipaddress_private. Instead of containing the first IP address they find, they contain the first public or private IP address. I also have two facts, on_public and on_private, that report whether a server has any public or private IP address. Here is how my previous example looks with these new facts.

ipaddress => 172.16.32.48
ipaddress_bond0 => 172.16.32.48
ipaddress_eth0 => 192.0.32.10
ipaddress_private => 172.16.32.48
ipaddress_public => 192.0.32.10
on_private => true
on_public => true

The code for the facts is below.

require 'facter/util/ip'
 
def has_address(interface)
  ip = Facter::Util::IP.get_interface_value(interface, 'ipaddress')
  if ip.nil?
    false
  else
    true
  end
end
 
def is_private(interface)
  rfc1918 = Regexp.new('^10\.|^172\.(?:1[6-9]|2[0-9]|3[0-1])\.|^192\.168\.')
  ip = Facter::Util::IP.get_interface_value(interface, 'ipaddress')
  if rfc1918.match(ip)
    true
  else
    false
  end
end
 
def find_networks
  found_public = found_private = false
  Facter::Util::IP.get_interfaces.each do |interface|
    if has_address(interface)
      if is_private(interface)
        found_private = true
      else
        found_public = true
      end
    end
  end
  [found_public, found_private]
end
 
# these facts check if any interface is on a public or private network
# they return the string true or false
# this fact will always be present
 
Facter.add(:on_public) do
  confine :kernel => Facter::Util::IP.supported_platforms
  setcode do
    found_public, found_private = find_networks
    found_public
  end
end
 
Facter.add(:on_private) do
  confine :kernel => Facter::Util::IP.supported_platforms
  setcode do
    found_public, found_private = find_networks
    found_private
  end
end
 
# these facts return the first public or private ip address found
# when iterating over the interfaces in alphabetical order
# if no matching address is found the fact won't be present
 
Facter.add(:ipaddress_public) do
  confine :kernel => Facter::Util::IP.supported_platforms
  setcode do
    ip=""
    Facter::Util::IP.get_interfaces.each do |interface|
      if has_address(interface)
        if not is_private(interface)
          ip = Facter::Util::IP.get_interface_value(interface, 'ipaddress')
          break
        end
      end
    end
    ip
  end
end
 
Facter.add(:ipaddress_private) do
  confine :kernel => Facter::Util::IP.supported_platforms
  setcode do
    ip=""
    Facter::Util::IP.get_interfaces.each do |interface|
      if has_address(interface)
        if is_private(interface)
          ip = Facter::Util::IP.get_interface_value(interface, 'ipaddress')
          break
        end
      end
    end
    ip
  end
end