Ansible: Merge variable values into new variable

Let's say I have an inventory like this:

database:
  hosts:
    database1:
      ansible_host: 192.168.0.125
    database2:
      ansible_host: 192.168.0.126
    database3:
      ansible_host: 192.168.0.127

Now I'll have to replace a string in a file that has the IP addresses of all hosts and hosts from the future as well. So in short, I need a variable that looks like this:

192.168.0.125,192.168.0.126,192.168.0.127

Now, I could just do this:

Inventory:

database:
  hosts:
    database1:
      ansible_host: 192.168.0.124
    database2:
      ansible_host: 192.168.0.126
    database3:
      ansible_host: 192.168.0.127
  vars:
      dbs: "{{ hostvars['database1']['ansible_host'] + ',' + hostvars['database2']['ansible_host'] + ',' + hostvars['database3']['ansible_host'] }}"

Playbook:

- name: Show host's ip
    debug:
      msg: "{{ dbs }}"

But this clearly is not good, cause if a new instance comes in this list, I'll have to add manualla + ',' + hostvars['databaseX']['ansible_host'] to the inventory and I wish to avoid that.

Can you guys recommend a way to use a loop or items list to get the string in a variable with all the IP addresses?

Thanks !

Solution

Create the variable dynamically in the inventory. For example,

shell> cat hosts
database:
  hosts:
    database1:
      ansible_host: 192.168.0.124
    database2:
      ansible_host: 192.168.0.126
    database3:
      ansible_host: 192.168.0.127
  vars:
    dbs: "{{ groups.database|
             map('extract', hostvars, 'ansible_host')|
             join(',') }}"

^{Example of a complete playbook for testing
shell> cat pb.yml
- hosts: all
tasks:
- debug:
var: dbs

gives
shell> ansible-playbook pb.yml

PLAY [all] ***********************************************************************************

TASK [debug] *********************************************************************************
ok: [database1] =>
dbs: 192.168.0.124,192.168.0.126,192.168.0.127
ok: [database3] =>
dbs: 192.168.0.124,192.168.0.126,192.168.0.127
ok: [database2] =>
dbs: 192.168.0.124,192.168.0.126,192.168.0.127

PLAY RECAP ***********************************************************************************
database1: ok=1 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
database2: ok=1 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
database3: ok=1 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0}