Loop Over Dictionary Attribute in Ansible

Working with variables can sometimes get tricky in Ansible. Say, you have a dictionary where you want loop over a certain attribute, not all values. For example, when your variables are declared like this:

interfaces:
  eth0:
    ip: 10.0.0.10
    mask: 16
  eth1:
    ip: 192.168.1.100
    mask: 24

How do you just loop over all the IP addresses? This is where the map filter comes in:

vars:
  ip_addresses: "{{ interfaces.values() | map(attribute='container') | list }}"

The snippet takes all values from the interfaces dictionary (eth0, eth1) and then extracts the ip attribute from them. Finally, it casts the result into list.

Ansible filters are a very powerful tool, so I would recommend you take some time to read it thoroughly. If you are looking for more Ansible tips, such as how to make a playbook distribution agnostic or setup your laptop with Ansible, look here.