How to catch and re-raise errors in Ansible

The following is based on the latest version of Ansible 2.9 and 2.10 as of November 13, 2020.

Intro

There are cases where you are using a role from inside a block, and the role itself uses a block, and you want to propagate errors from the inner block to be handled in a rescue in an outer block, and you want access to the ansible_failed_result from the inner block.

---
- name: test nested blocks
  hosts: localhost
  tasks:
    - block:
        - name: first outer level task
          debug:
            msg: first outer level task
        - block:
            - name: first inner level task
              debug:
                msg: first inner level task
            - name: inner task that fails
              fail:
                msg: inner task that fails
            - name: inner task that should never execute
              debug:
                msg: inner task that should never execute
        - name: second outer level task
          debug:
            msg: second outer level task
      rescue:
        - name: outer block rescue task
          debug:
            msg: outer block rescue task ansible_failed_result is {{ ansible_failed_result | d("undefined") | to_nice_json }}
        - name: check for error message
          assert:
            that: ansible_failed_result.msg == "inner task that fails"

This case works fine - the error from the inner block is correctly propagated to the rescue in the outer block with the correct context information.

Problem - ansible_failed_result is undefined

The problem arises when you want to use always or rescue in the inner block:

...
        - block:
            - name: first inner level task
              debug:
                msg: first inner level task
            - name: inner task that fails
              fail:
                msg: inner task that fails
            - name: inner task that should never execute
              debug:
                msg: inner task that should never execute

          always:
            - name: inner always task
              debug:
                msg: inner always task e.g. remove temporary directory
...

The outer rescue block is still called, which means an error was detected by Ansible and handled, but the context information is gone and ansible_failed_result is undefined:

TASK [outer block rescue task] *************************************************
task path: /home/rmeggins/ansible_sandbox/nested-block-two.yml:27
ok: [localhost] => {}

MSG:

outer block rescue task ansible_failed_result is "undefined"

TASK [check for error message] *************************************************
task path: /home/rmeggins/ansible_sandbox/nested-block-two.yml:30
fatal: [localhost]: FAILED! => {}

MSG:

The conditional check 'ansible_failed_result.msg == "inner task that fails"' failed. The error was: error while evaluating conditional (ansible_failed_result.msg == "inner task that fails"): 'ansible_failed_result' is undefined

Same if a rescue is used in the inner block, with or without the always.

Solution - re-raise the ansible_failed_result

You can re-raise the error with the ansible_failed_result by using it as the only value for a fail module msg argument:

...
        - block:
            - name: first inner level task
              debug:
                msg: first inner level task
            - name: inner task that fails
              fail:
                msg: inner task that fails
            - name: inner task that should never execute
              debug:
                msg: inner task that should never execute
          rescue:
            - name: re-raise the error
              fail:
                msg: "{{ ansible_failed_result }}"
          always:
            - name: inner always task
              debug:
                msg: inner always task e.g. remove temporary directory
...

Now we get the desired result:

TASK [outer block rescue task] *************************************************
task path: /home/rmeggins/ansible_sandbox/nested-block.yml:38
ok: [localhost] => {}

MSG:

outer block rescue task ansible_failed_result is {
    "_ansible_no_log": false,
    "changed": false,
    "failed": true,
    "msg": "inner task that fails"
}

TASK [check for error message] *************************************************
task path: /home/rmeggins/ansible_sandbox/nested-block.yml:41
ok: [localhost] => {
    "changed": false
}

MSG:

All assertions passed

Here is the complete example, with some extra tasks to show the behavior:

---
- name: test nested blocks
  hosts: localhost
  tasks:
    - block:
        - name: first outer level task
          debug:
            msg: first outer level task
        - block:
            - name: first inner level task
              debug:
                msg: first inner level task
            - name: inner task that fails
              fail:
                msg: inner task that fails
            - name: inner task that should never execute
              debug:
                msg: inner task that should never execute
          rescue:
            - name: inner block rescue task
              debug:
                msg: inner block rescue task ansible_failed_result is {{ ansible_failed_result | d("undefined") | to_nice_json }}
            - name: re-raise error
              fail:
                msg: "{{ ansible_failed_result }}"
          always:
            - name: first inner block always task
              debug:
                msg: first inner block always task ansible_failed_result is {{ ansible_failed_result | d("undefined") | to_nice_json }}
        - block:
            - name: second block inner level task
              debug:
                msg: second block inner level task
        - name: second outer level task
          debug:
            msg: second outer level task
      rescue:
        - name: outer block rescue task
          debug:
            msg: outer block rescue task ansible_failed_result is {{ ansible_failed_result | d("undefined") | to_nice_json }}
        - name: check for error message
          assert:
            that: ansible_failed_result.msg == "inner task that fails"

Run like this:

ANSIBLE_STDOUT_CALLBACK=debug \
ansible-playbook -vv nested-block-re-raise.yml