Ansible: Example of working with lists of host vars

ansible-ip-list-play.yml

---
- hosts: servers
  gather_facts: true
  sudo: true

  vars:
     fail2ban_config_ignoreip:
        - "127.0.0.1/8"
        - "{{ ansible_ssh_host }}"

  tasks:

   - debug: msg="{{ groups['servers'] }}"

   - name: get hostvars for servers' ansible_default_ipv4
     set_fact:
        ip_list1: "{{ hostvars|fetchlistfromdict(groups.servers)|map(attribute='ansible_default_ipv4.address')|list }}"

   - name: Show the list of ansible_default_ipv4
     debug: msg="{{ ip_list1 }}"


   - name: Get the servers' ansible_all_ipv4_addresses
     set_fact:
       ip_list2: "{{hostvars|fetchlistfromdict(groups.servers)|map(attribute='ansible_all_ipv4_addresses')|list }}"

   - name: Show the list we obtained for ansible_all_ipv4_addresses
     debug: msg="{{ip_list2}}"


   - name: Flatten the list of ansible_all_ipv4_addresses
     set_fact:
        ip_list3:  "{{ ip_list2 | flatten_dict_values }}"

   - debug: msg="{{ ip_list3 }}"


   - name: Join all of the lists
     set_fact:
        ip_list4: "{{ fail2ban_config_ignoreip | union(ip_list1) | union(ip_list3) }}"

   - name: show the final list
     debug: msg="{{ ip_list4 }}"

ansible-ip-list-readme.MD

An additional example of creating a list from a dictionary var using Jinja filters in an ansible play task. see article: http://www.blue-bag.com/blog/ansible-filters-taming-lists-part-2

flatten_dict_values.py

# This function will take a dictionary composed of sub arrays
# and flatten it
# e.g.
# [[u'46.101.45.8', u'10.131.174.53'], [u'46.101.45.10', u'10.131.174.54']]
#  to
#  [u'46.101.45.8', u'10.131.174.53', u'46.101.45.10', u'10.131.174.54']

def flatten_dict_values(dictionary):
    result = []
    result = reduce(list.__add__, dictionary,[])
    return result

class FilterModule (object):
    def filters(self):
        return {
            "flatten_dict_values": flatten_dict_values
        }

# http://feldboris.alwaysdata.net/blog/python-trick-how-to-flatten-dictionaries-values-composed-of-iterables.html
# http://stackoverflow.com/questions/15995/useful-code-which-uses-reduce-in-python

x-ip-list.log

$ ansible-playbook ip_lists.yml -K
SUDO password:

PLAY [servers] ****************************************************************

GATHERING FACTS ***************************************************************
ok: [web01.example.co.uk]
ok: [db01.example.co.uk]

TASK: [debug msg="{{ groups['servers'] }}"] ***********************************
ok: [web01.example.co.uk] => {
    "msg": "['web01.example.co.uk', 'db01.example.co.uk']"
}
ok: [db01.example.co.uk] => {
    "msg": "['web01.example.co.uk', 'db01.example.co.uk']"
}

TASK: [get hostvars for servers' ansible_default_ipv4] ************************
ok: [db01.example.co.uk]
ok: [web01.example.co.uk]

TASK: [Show the list of ansible_default_ipv4] *********************************
ok: [web01.example.co.uk] => {
    "msg": "[u'1.2.3.4', u'1.2.3.5']"
}
ok: [db01.example.co.uk] => {
    "msg": "[u'1.2.3.4', u'1.2.3.5']"
}

TASK: [Get the servers' ansible_all_ipv4_addresses] ***************************
ok: [web01.example.co.uk]
ok: [db01.example.co.uk]

TASK: [Show the list we obtained for ansible_all_ipv4_addresses] **************
ok: [db01.example.co.uk] => {
    "msg": "[[u'1.2.3.4', u'10.10.20.1'], [u'1.2.3.5', u'10.10.20.2']]"
}
ok: [web01.example.co.uk] => {
    "msg": "[[u'1.2.3.4', u'10.10.20.1'], [u'1.2.3.5', u'10.10.20.2']]"
}

TASK: [Flatten the list of ansible_all_ipv4_addresses] ************************
ok: [db01.example.co.uk]
ok: [web01.example.co.uk]

TASK: [debug msg="{{ ip_list3 }}"] ********************************************
ok: [db01.example.co.uk] => {
    "msg": "[u'1.2.3.4', u'10.10.20.1', u'1.2.3.5', u'10.10.20.2']"
}
ok: [web01.example.co.uk] => {
    "msg": "[u'1.2.3.4', u'10.10.20.1', u'1.2.3.5', u'10.10.20.2']"
}

TASK: [Join all of the lists] *************************************************
ok: [web01.example.co.uk]
ok: [db01.example.co.uk]

TASK: [show the final list] ***************************************************
ok: [web01.example.co.uk] => {
    "msg": "['127.0.0.1/8', u'1.2.3.4', u'1.2.3.5', u'10.10.20.1', u'10.10.20.2']"
}
ok: [db01.example.co.uk] => {
    "msg": "['127.0.0.1/8', u'1.2.3.5', u'1.2.3.4', u'10.10.20.1', u'10.10.20.2']"
}

PLAY RECAP ********************************************************************
db01.example.co.uk            : ok=10   changed=0    unreachable=0    failed=0
web01.example.co.uk           : ok=10   changed=0    unreachable=0    failed=0

Instead of fetchlistfromdict the new method is to use the extract filter with a map.

This StackOverflow Answer does a great job of answering.

There's also the new json_query filter in 2.2, but I'm not sure how to use it for this case.