Ansible – Check if Variable Exists in Attribute List

ansiblejinja2yaml

I have a variable containing details of host machines on my network (called 'hostlist' – I believe you call this a dictionary, but I'm not sure of the terminology. The variable is defined in a file in group_vars/all, so it's available in all playbooks (not sure if this is important).

I have a play which I would like to run only if ansible_hostname is not found in the list of host names in hostlist. The host names in hostlist are one of the attributes of the variable, but again I'm not sure if "attribute" is the right term…

Hostlist is defined as:

hostlist:
  - { name: 'host1', ip_addr: '192.168.2.31', hostgrp: 'physical_workstation' }
  - { name: 'host2', ip_addr: '192.168.2.32', hostgrp: 'physical_workstation' }
  - { name: 'host3', ip_addr: '192.168.2.33', hostgrp: 'virtual_machine' }

The play I'm using to try to get this working is:

- name: Conditional test
  debug:
    msg: "ansible_hostname not found in hostlist."
  when: ansible_hostname not in hostlist.name

I'm not sure of the syntax required in the condition, or if what I'm wanting is achieveable in this manner?

Best Answer

There are presumably more elegant ways of doing it, but something like this works for me:

If your inventory file looks like this

host1
host2
host3
host4

Then a playbook with the following content, would only be run against host4 because it isn't matched in the hostlist var:
$ cat test.yml

- hosts: all
  vars:
    hostlist:
      - { name: 'host1', ip_addr: '192.168.2.31', hostgrp: 'physical_workstation' }
      - { name: 'host2', ip_addr: '192.168.2.32', hostgrp: 'physical_workstation' }
      - { name: 'host3', ip_addr: '192.168.2.33', hostgrp: 'virtual_machine' }
  tasks:

    - name: Conditional test
      debug:
        msg: "ansible_hostname not found in hostlist."
      when: hostlist|selectattr("name", "equalto", ansible_hostname)|list|length == 0

when called like this:

ansible-playbook test.yml

means that only host4 runs the block of tasks....

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

TASK [Gathering Facts] *************************************
ok: [host1]
ok: [host2]
ok: [host3]
ok: [host4]

TASK [debug] ***********************************************
ok: [host4] => {
    "msg": "hostname not in hostlist name list"
}
skipping: [host1]
skipping: [host2]
skipping: [host3]
Related Topic