ansible/docs/docsite/rst/user_guide/playbooks_blocks.rst
Andreas Olsson 1a11cecaef Prefer https:// links in the docs site
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2018-08-01 08:20:40 -07:00

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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 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.
.. code-block:: YAML
:emphasize-lines: 3
:caption: Block example
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.
.. versionadded:: 2.3
The ``name:`` keyword for ``block:`` was added in Ansible 2.3.
.. _block_error_handling:
Error Handling
``````````````
Blocks also introduce the ability to handle errors in a way similar to exceptions in most programming languages.
.. code-block:: YAML
:emphasize-lines: 3,9,15
:caption: Block error handling example
tasks:
- name: Attempt and graceful roll back demo
block:
- debug:
msg: 'I execute normally'
- command: /bin/false
- debug:
msg: 'I never execute, due to the above task failing'
rescue:
- debug:
msg: 'I caught an error'
- 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 :
.. code-block:: YAML
:emphasize-lines: 6,10
:caption: Block run handlers in error handling
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'
.. versionadded:: 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.
.. seealso::
:doc:`playbooks`
An introduction to playbooks
:doc:`playbooks_reuse_roles`
Playbook organization by roles
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