Special ansible variable 'omit' gets interpreted as ssh user when used with `delegate_to` and `remote_user`

[golebiewsky]

Hello, I've commented on this closed issue https://github.com/mitogen-hq/mitogen/issues/1040 - but opening new one for visibility.

On mitogen 0.3.18 I had to add

self._connection._play_context.post_validate(templar=connection.templar)

as mentioned in first comment of https://github.com/mitogen-hq/mitogen/issues/1040. With that patch all of my playbooks worked without hiccups after upgrading from mitogen 0.3.9.

I was hoping to now migrate from mitogen 0.3.18 to mitogen 0.3.22, since issue was closed and many other improvements were made to mitogen.

I noticed that using omit with delegate_to: and with remote_user: can make ssh use omit value as ssh user.

e.g. I will try to omit remote_user, by not defining test variable

- name: Test
  hosts: all
  gather_facts: false
  tasks:
    - name: Touch file using file module
      ansible.builtin.file:
        path: /tmp/test
        state: touch
      remote_user: "{{ test | default(omit) }}"
      delegate_to: 1.2.3.4

In mitogen 0.3.18 (with the patch), ssh user is just not forwarded so default will be used:

[mux  93383] 18:18:18.765805 D mitogen.parent: creating connection to context 2 using mitogen.ssh
[mux  93383] 18:18:18.765558 D mitogen.io: PollPoller.poll(None)
[mux  93383] 18:18:18.810675 D mitogen.parent: command line for Connection(None): ssh -o "LogLevel ERROR" -o "Compression yes" ...

In mitogen 0.3.22, it tries to use value of omit as actual user

[mux  93949] 18:22:39.322810 D mitogen.parent: creating connection to context 2 using mitogen.ssh
[mux  93949] 18:22:39.322571 D mitogen.io: PollPoller.poll(None)
[mux  93949] 18:22:39.350936 D mitogen.parent: command line for Connection(None): ssh -o "LogLevel ERROR" -l __omit_place_holder__12cecd4460ad11a8ab6a9edbde1b2af5a4505b42 -o "Compression yes" ...

Without delegate_to: it works in both versions, but there are special cases where I need to use both.. I would appreciate any tips related to this.

• Which version of Ansible are you running? 2.16.13
• Is your version of Ansible patched in any way? No
• Are you running with any custom modules, or module_utils loaded? No
• Have you tried the latest master version from Git? Tested on 0.3.22, it used to work on 0.3.9
• Mention your host and target OS and versions Host: macOS/Ubuntu 22.04, Target: Ubuntu 22.04 LTS
• Mention your host and target Python versions Host: Python 3.12.9, Target: Python 3.10.12

[moreati]

This looks like an upstream Ansible issue to me. I can reproduce it without Mitogen, e.g.

- hosts: d13.lan
  gather_facts: false
  vars:
    ansible_python_interpreter: python3
  tasks:
    - file:
        path: /tmp/mitogen-issue1250
        mode: u=rw,go=
        state: touch
    - file:
        path: /tmp/mitogen-issue1250-delegate
        mode: u=rw,go=
        state: touch
      delegate_to: d12.lan
    - file:
        path: /tmp/mitogen-issue1250-delegate-ruser-omit
        mode: u=rw,go=
        state: touch
      delegate_to: d12.lan
      remote_user: "{{ variable_intentionally_undefined | default(omit) }}"

➜  mitogen git:(master) ✗ ANSIBLE_STRATEGY=linear ansible-playbook issue1250.yml

PLAY [d13.lan] *******************************************************************************************

TASK [file] **********************************************************************************************
changed: [d13.lan]

TASK [file] **********************************************************************************************
changed: [d13.lan -> d12.lan]

TASK [file] **********************************************************************************************
fatal: [d13.lan -> d12.lan]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: __omit_place_holder__2414c3f6600f005398ab5de9a4823e2cf44b8d48@d12.lan: Permission denied (publickey,password).", "unreachable": true}

PLAY RECAP ***********************************************************************************************
d13.lan                    : ok=2    changed=2    unreachable=1    failed=0    skipped=0    rescued=0    ignored=0