Ansible task is run regardless of condition

Question

If I store a string into an ansible register, and then have other tasks run only when that register contains a certain value, they are always run, regardless of the value in the register.

Why is ansible running tasks when a conditional should fail?

This is a simple example. It should only debug once (as test_foo.stdout == "Foo") but instead it will print both debug statements:

- name: foo
  command: "echo \"Foo\""
  register: test_foo
  tags: [ 'foo-test' ]

- debug:
    var: test_foo
  when: test_foo.stdout == "Foo",
  tags: [ 'foo-test' ]

- debug:
    var: test_foo
  when: test_foo.stdout == "Bar",
  tags: [ 'foo-test' ]

Just to note, this also happens when another command call is triggered with the same conditional, not just debug calls. It will always execute both tasks.

Here's the output:

TASK [test : foo] ***********************************************************************************************************************************************************************************
changed: [localServer -> localhost] => {"changed": true, "cmd": ["echo", "Foo"], "delta": "0:00:01.002745", "end": "2020-11-17 11:22:25.733089", "rc": 0, "start": "2020-11-17 11:22:24.730344", "stderr": "", "stderr_lines": [], "stdout": "Foo", "stdout_lines": ["Foo"]}

TASK [test : debug] *********************************************************************************************************************************************************************************
ok: [localServer] => {
    "test_foo": {
        "changed": true,
        "cmd": [
            "echo",
            "Foo"
        ],
        "delta": "0:00:01.002745",
        "end": "2020-11-17 11:22:25.733089",
        "failed": false,
        "rc": 0,
        "start": "2020-11-17 11:22:24.730344",
        "stderr": "",
        "stderr_lines": [],
        "stdout": "Foo",
        "stdout_lines": [
            "Foo"
        ]
    }
}

TASK [test : debug] *********************************************************************************************************************************************************************************
ok: [localServer] => {
    "test_foo": {
        "changed": true,
        "cmd": [
            "echo",
            "Foo"
        ],
        "delta": "0:00:01.002745",
        "end": "2020-11-17 11:22:25.733089",
        "failed": false,
        "rc": 0,
        "start": "2020-11-17 11:22:24.730344",
        "stderr": "",
        "stderr_lines": [],
        "stdout": "Foo",
        "stdout_lines": [
            "Foo"
        ]
    }
}

And just in case this something weirdly version specific, I'm on Ubuntu 20.04 and this is my version:

$ ansible --version
ansible 2.9.6
  config file = /path/to/project/orchestration/ansible.cfg
  configured module search path = ['/home/myUser/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3/dist-packages/ansible
  executable location = /usr/bin/ansible
  python version = 3.8.5 (default, Jul 28 2020, 12:59:40) [GCC 9.3.0]

Answer 1

The problem is the trailing comma. The task below works as expected and gives "msg: false"

    - debug:
        msg: '{{ "A" == "B" }}'

The trailing comma creates a tuple

    - debug:
        msg: '{{ "A" == "B", }}'
    - debug:
        msg: "{{ (false,)|type_debug }}"

gives

  msg: (False,)

  msg: tuple

Non-empty variables, including tuples, evaluate to true

    - debug:
        msg: OK
      when: (A,)

gives

  msg: OK

See CONDITIONAL_BARE_VARS

Answer 2

I have just copied your code into my lab VM and I noticed you are using a comma at the end of the "when" statement (Which I have never seen). I have removed them and get expected output.

When variable is Foo:

PLAY [localhost] ***************************************************************************************************************

TASK [foo] *********************************************************************************************************************
changed: [localhost]

TASK [debug] *******************************************************************************************************************
ok: [localhost] => {
    "test_foo": {
        "changed": true,
        "cmd": [
            "echo",
            "Foo"
        ],
        "delta": "0:00:00.006168",
        "end": "2020-11-17 12:50:11.863107",
        "failed": false,
        "rc": 0,
        "start": "2020-11-17 12:50:11.856939",
        "stderr": "",
        "stderr_lines": [],
        "stdout": "Foo",
        "stdout_lines": [
            "Foo"
        ]
    }
}

TASK [debug] *******************************************************************************************************************
skipping: [localhost]

PLAY RECAP *********************************************************************************************************************
localhost                  : ok=2    changed=1    unreachable=0    failed=0

When variable is Bar:

PLAY [localhost] ***************************************************************************************************************

TASK [foo] *********************************************************************************************************************
changed: [localhost]

TASK [debug] *******************************************************************************************************************
skipping: [localhost]

TASK [debug] *******************************************************************************************************************
ok: [localhost] => {
    "test_foo": {
        "changed": true,
        "cmd": [
            "echo",
            "Bar"
        ],
        "delta": "0:00:00.006077",
        "end": "2020-11-17 12:53:24.142058",
        "failed": false,
        "rc": 0,
        "start": "2020-11-17 12:53:24.135981",
        "stderr": "",
        "stderr_lines": [],
        "stdout": "Bar",
        "stdout_lines": [
            "Bar"
        ]
    }
}

PLAY RECAP *********************************************************************************************************************
localhost                  : ok=2    changed=1    unreachable=0    failed=0

My ansible version is:

ansible 2.7.10
python version = 2.7.5