How to fetch remote file only if file does not already exist in Ansible

Question

In Ansible, I want to fetch a remote file, using the Fetch module, only if the file does not already exist at the destination. How could I do this? It doesn't seem like Fetch has an existing parameter to check for this.

My task:

- name: Fetch file from remote host
  fetch: 
    dest: /path/filename.{{groups['host'][0]}}.pub
    src: /path/filename.pub
    flat: yes
  delegate_to: "{{groups['host'][0]}}"

Thanks in advance!

Answer 1

Q: "Fetch module, only if the file does not already exist at the destination."

A: The fetch module is idempotent and downloads only changed file. For example the first run of the playbook

- hosts: test_01
  tasks:
    - fetch:
        dest: /tmp/fetched
        src: /etc/passwd
        flat: yes

gives

TASK [fetch] *********************************************************************************************************************************
changed: [test_01]

PLAY RECAP ***********************************************************************************************************************************
test_01                    : ok=1    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0 

Repeated run of the same playbook gives

TASK [fetch] *********************************************************************************************************************************
ok: [test_01]

PLAY RECAP ***********************************************************************************************************************************
test_01                    : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

The source shows that the file will be fetched only if the remote and local checksums differ.