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

Blocks

Blocks create logical groups of tasks. Blocks also offer ways to handle task errors, similar to exception handling in many programming languages.

Grouping tasks with blocks

All tasks in a block inherit directives applied at the block level. Most of what you can apply to a single task (with the exception of loops) can be applied at the block level, so blocks make it much easier to set data or directives common to the tasks. The directive does not affect the block itself, it is only inherited by the tasks enclosed by a block. For example, a when statement is applied to the tasks within a block, not to the block itself.

tasks:
  - name: Install, configure, and start Apache
    block:
      - name: install httpd and memcached
        yum:
          name:
          - httpd
          - memcached
          state: present
      - name: apply the foo config template
        template:
          src: templates/src.j2
          dest: /etc/foo.conf
      - name: start service bar and enable it
        service:
          name: bar
          state: started
          enabled: True
    when: ansible_facts['distribution'] == 'CentOS'
    become: true
    become_user: root
    ignore_errors: yes

In the example above, the 'when' condition will be evaluated before Ansible runs each of the three tasks in the block. All three tasks also inherit the privilege escalation directives, running as the root user. Finally, ignore_errors: yes ensures that Ansible continues to execute the playbook even if some of the tasks fail.

Names for tasks within blocks have been available since Ansible 2.3. We recommend using names in all tasks, within blocks or elsewhere, for better visibility into the tasks being executed when you run the playbook.

Handling errors with blocks

You can control how Ansible responds to task errors using blocks with rescue and always sections.

Rescue blocks specify tasks to run when an earlier task in a block fails. This approach is similar to exception handling in many programming languages. Ansible only runs rescue blocks after a task returns a 'failed' state. Bad task definitions and unreachable hosts will not trigger the rescue block.

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, :-)'

You can also add an always section to a block. Tasks in the always section run no matter what the task status of the previous block 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, :-)"

Together, these elements offer 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 execute normally. If any tasks in the block return failed, the rescue section executes tasks to recover from the error. The always section runs regardless of the results of the block and rescue sections.

If an error occurs in the block and the rescue task succeeds, Ansible reverts the failed status of the original task for the run and continues to run the play as if the original task had succeeded. The rescued task is considered successful, and does not not trigger max_fail_percentage or any_errors_fatal configurations. However, Ansible still reports a failure in the playbook statistics.

You can use blocks with flush_handlers in a rescue task to ensure that all handlers run even if an error occurs:

tasks:
  - name: Attempt and graceful roll back demo
    block:
      - debug:
          msg: 'I execute normally'
        changed_when: yes
        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 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_intro

An introduction to playbooks

playbooks_reuse_roles

Playbook organization by roles

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