ansible/docs/docsite/rst/user_guide/playbooks_blocks.rst

Blocks

Blocks allow for logical grouping of tasks and in play error handling. Most of what you can apply to a single task (with the exception of loops) can be applied at the block level, which also makes it much easier to set data or directives common to the tasks. This does not mean the directive affects the block itself, but is inherited by the tasks enclosed by a block. i.e. a when will be applied to the tasks, not the block itself.

tasks:
  - name: Install Apache
    block:
      - yum:
          name: "{{ item }}"
          state: installed
        with_items:
          - httpd
          - memcached
      - template:
          src: templates/src.j2
          dest: /etc/foo.conf
      - service:
          name: bar
          state: started
          enabled: True
    when: ansible_distribution == 'CentOS'
    become: true
    become_user: root

In the example above, each of the 3 tasks will be executed after appending the when condition from the block and evaluating it in the task's context. Also they inherit the privilege escalation directives enabling "become to root" for all the enclosed tasks.

2.3

The name: keyword for block: was added in Ansible 2.3.

Error Handling

Blocks also introduce the ability to handle errors in a way similar to exceptions in most programming languages. Blocks only deal with 'failed' status of a task. A bad task definition, an undefined variable or an unreachable host are not rescuable errors.

tasks: - name: Handle the error block: - debug: msg: 'I execute normally' - name: i force a failure command: /bin/false - debug: msg: 'I never execute, due to the above task failing, :-(' rescue: - debug: msg: 'I caught an error, can do stuff here to fix it, :-)'

This will 'revert' the failed status of the task for the run and the play will continue as if it had succeeded.

There is also an always section, that will run no matter what the task status is.

• name: Always do X block: - debug: msg: 'I execute normally' - name: i force a failure command: /bin/false - debug: msg: 'I never execute :-(' always: - debug: msg: "This always executes, :-)"

They can be added all together to do complex error handling.

- name: Attempt and graceful roll back demo
  block:
    - debug:
        msg: 'I execute normally'
    - name: i force a failure
      command: /bin/false
    - debug:
        msg: 'I never execute, due to the above task failing, :-('
  rescue:
    - debug:
        msg: 'I caught an error'
    - name: i force a failure in middle of recovery! >:-)
      command: /bin/false
    - debug:
        msg: 'I also never execute :-('
  always:
    - debug:
        msg: "This always executes"

The tasks in the block would execute normally, if there is any error the rescue section would get executed with whatever you need to do to recover from the previous error. The always section runs no matter what previous error did or did not occur in the block and rescue sections. It should be noted that the play continues if a rescue section completes successfully as it 'erases' the error status (but not the reporting), this means it won't trigger max_fail_percentage nor any_errors_fatal configurations but will appear in the playbook statistics.

Another example is how to run handlers after an error occurred :

tasks:
  - name: Attempt and graceful roll back demo
    block:
      - debug:
          msg: 'I execute normally'
        notify: run me even after an error
      - command: /bin/false
    rescue:
      - name: make sure all handlers run
        meta: flush_handlers
handlers:
   - name: run me even after an error
     debug:
       msg: 'This handler runs even on error'

2.1

Ansible also provides a couple of variables for tasks in the rescue portion of a block:

ansible_failed_task

The task that returned 'failed' and triggered the rescue. For example, to get the name use ansible_failed_task.name.

ansible_failed_result

The captured return result of the failed task that triggered the rescue. This would equate to having used this var in the register keyword.

playbooks

An introduction to playbooks

playbooks_reuse_roles

Playbook organization by roles

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