Deal with NICs in Ansible without knowing what udev/systemd will call them

Intro.txt

Scenario:

You are building a load balancer wherein you want to bond the interfaces that will be used to serve the traffic.
You're managing this via Ansible. You don't want to have to boot to an OS to see what udev/system will name the
NICs you intend to bond, because that is just stupid. So you decide to work with the MAC addresses. Oops,
the `ansible_facts` don't make that easy.

Solution:

The convoluted trickery published here.

macfaces.py

#!/bin/env python
# put this in your playbook's "library" directory
import os
import json

def file_get_contents(filename):
  with file(filename) as f:
    s = f.read()
  return s

ifaceNames = os.listdir('/sys/class/net/')
result = dict()

for iface in ifaceNames:
  mac = file_get_contents('/sys/class/net/' + iface + '/address').strip()
  result[mac] = iface

print json.dumps(result)

nics.yml

- name: add bond interface
  template:
    src: templates/bond-iface.cfg
    dest: "/etc/sysconfig/network-scripts/ifcfg-{{bond_iface}}"
  notify:
    - restart network

- name: map macs to iface names
  macfaces:
    nothing: 'no input needed'
  register: ifaces

- name: merge iface data
  set_fact:
    iface: "{{ dict(device=ifaces[item.mac_address]) | combine(item) }}"
  register: merged_iface_data
  with_items: "{{slave_nics}}"

- name: add slave interfaces
  template:
    src: templates/slave-iface.cfg
    dest: "/etc/sysconfig/network-scripts/ifcfg-{{iface.device}}"
  with_items: "{{merged_iface_data.results}}"
  vars:
    iface: "{{item.ansible_facts.iface}}"
    device: "{{iface.device}}"
    uuid: "{{iface.uuid}}"
    mac_address: "{{iface.mac_address}}"
    master: "{{iface.master}}"
  notify:
    - restart network

vars.yml

# These rules are used to configure the bond interface that is used
# to handle all traffic on the load balancer.
bond_iface: bond0
bond_iface_mac: b3:3b:b8:f3:47:zz
bond_ip_address: 172.25.50.zz
bond_netmasK: 255.255.255.0
bond_gateway: 172.25.50.1
bond_dns1: 168.28.240.81
bond_dns2: 168.28.240.82
bond_opts: 'mode=balance-alb miimon=100'

# These variables define all of the interfaces that will be used by the
# bond interface to let it do its thing. Notice that we are not listing the
# interface names. We are matching based on MAC since there's no telling
# what the names could be.
slave_nics:
  - mac_address: 00:00:00:aa:bb:cc
    uuid: 1A87ED79-0D4A-4888-96CE-3879B8BFF1zz
    master: "{{bond_iface}}"
  - mac_address: 00:00:00:aa:bb:dd
    uuid: B5E8399D-93D3-4915-9847-E83927260Czz
    master: "{{bond_iface}}"