Ansible: assign and loop through list dynamically

I'm new at Ansible and trying to automate a Fortigate configuration using the fortinet.fortios modules.

I'm having a problem with fortios_firewall_addrgrp specifically that does not support the append of a firewall address to a group.

I have this set in my variables:

addresses:
  host_0:
    subnet: 192.168.1.10/24
    group: group_0
  host_1:
    subnet: 192.168.1.11/24
    group: group_0
  host_2:
    subnet: 192.168.10.10/24
    group: group_1
  host_3:
    subnet: 192.168.10.11/24
    group: group_1

And I'm running this task to generate an address group.

- name: Configure IPv4 address groups.
  fortios_firewall_addrgrp:
    vdom: '{{ vdom }}'
    state: present
    firewall_addrgrp:
      name: '{{ item.value.group }}'
      member:
        - name: '{{ item.key }}'
  loop: '{{ addresses | dict2items }}'

It loops through each host and generates an address group, but it results in having 2 groups containing only the last hostname in the list.

Ideally, the module should support the append of a hostname to an existing group, but it doesn't, so I'm trying to work around it to make the following happening:

member:
  - name: host_0
  - name: host_1

The example above would work, but I cannot know in advance groups and hostnames in the variable.

I could generate or filter the input variable into a dictionary of host and groups and give it to members. Still, I cannot understand how to loop through it dynamically.

The problem you are having is related to the data structure you are using for the loop. As you mentioned, the fortios_firewall_addrgrp module expects a list of dictionaries for the members key, representing each host.

So, you need to create a new data structure that fits the input of the fortios_firewall_addrgrp module. Here is an example of how to do it:

---
- hosts: localhost
  gather_facts: 'no'
  vars:
    addresses:
      host_0:
        subnet: 192.168.1.10/24
        group: group_0
      host_1:
        subnet: 192.168.1.11/24
        group: group_0
      host_2:
        subnet: 192.168.10.10/24
        group: group_1
      host_3:
        subnet: 192.168.10.11/24
        group: group_1
  tasks:
    - set_fact:
        addresses_by_group: |
          {{
            addresses_by_group | default({}) | combine({
              item.value.group: (addresses_by_group[item.value.group] | default([])) + [{"name": item.key}]
            })
          }}
      loop: '{{ addresses | dict2items }}'
    - name: Configure IPv4 address groups.
      fortios_firewall_addrgrp:
        vdom: '{{ vdom }}'
        state: present
        firewall_addrgrp:
          name: '{{ item.key }}'
          member: '{{ item.value }}'
      loop: '{{ addresses_by_group | dict2items }}'

We create a new variable called addresses_by_group that will store a list of hosts for each group. The combine filter allows you to combine two different dictionaries, while the default filter sets a default value for an undefined variable. We use the + operator to concatenate two lists. If you debug the value of the variable addresses_by_group you'll see this:

TASK [debug] *******************************************************************
ok: [localhost] => 
  addresses_by_group:
    group_0:
    - name: host_0
    - name: host_1
    group_1:
    - name: host_2
    - name: host_3

Which is just what we need. Bear in mind that we didn't touch the addresses variables so that you can use them later on.