Blocks — Ansible Documentation

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# 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.

Block example with named tasks inside the block

     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, 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. Finally, `ignore_errors: yes` will continue executing 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.

## Blocks 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 or an unreachable host are not ‘rescuable’ errors.

Block error handling example

     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.

Block with always section

     - 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.

Block with all sections

    - 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 :

Block run handlers in error handling

     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'

New in version 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.

See also

Working With Playbooks
  An introduction to playbooks
Roles
  Playbook organization by roles
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  #ansible IRC chat channel