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Update playbooks_strategies.rst (#57784)

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* Update playbooks_strategies.rst

##### SUMMARY
This page is very confusing and may suggest, that there is still a `serial` strategy (like it used to), but now it is just a directive of `linear` strategy. Multiple people reported this to me and it needs change.


##### ISSUE TYPE
- Docs Pull Request

+label: docsite_pr

* Update docs/docsite/rst/user_guide/playbooks_strategies.rst

Co-Authored-By: Sam Doran <sdoran@redhat.com>

* Update docs/docsite/rst/user_guide/playbooks_strategies.rst

Co-Authored-By: Sam Doran <sdoran@redhat.com>

* Updates strategies page more broadly

* incorporate samdoran feedback

* fixes broken link

* new page title, focus on user intent

* more sdoran feedback

* adds details on setting the number of forks
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Lucian Maly 2019-06-19 06:52:01 +10:00 committed by Sandra McCann
parent 7765bd41e6
commit 446027341a
1 changed files with 29 additions and 16 deletions
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docs/docsite/rst/user_guide/playbooks_strategies.rst
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.. _playbooks_strategies:
Strategies
===========
Controlling playbook execution: strategies and more
===================================================
Strategies are a way to control play execution. By default, plays run with a ``linear`` strategy, in which all hosts will run each task before any host starts the next task, using the number of forks (default 5) to parallelize.
By default, Ansible runs each task on all hosts affected by a play before starting the next task on any host, using 5 forks. If you want to change this default behavior, you can use a different strategy plugin, change the number of forks, or apply one of several play-level keywords like ``serial``.
The ``serial`` directive can 'batch' this behaviour to a subset of the hosts, which then run to
completion of the play before the next 'batch' starts.
.. contents::
:local:
A second ``strategy`` ships with Ansible - ``free`` - which allows each host to run until the end of
the play as fast as it can.::
Selecting a strategy
--------------------
The default behavior described above is the :ref:`linear strategy<linear_strategy>`. Ansible offers other strategies, including the :ref:`debug strategy<debug_strategy>` (see also :ref:`playbook_debugger`) and the :ref:`free strategy<free_strategy>`, which allows
each host to run until the end of the play as fast as it can::
- hosts: all
strategy: free
tasks:
...
You can select a different strategy for each play as shown above, or set your preferred strategy globally in ``ansible.cfg``, under the ``defaults`` stanza::
Strategy Plugins
`````````````````
[defaults]
strategy = free
The strategies are implemented as plugins. In the future, new
execution strategies can be added, either locally by users or to Ansible itself by
a code contribution.
All strategies are implemented as :ref:`strategy plugins<strategy_plugins>`. Please review the documentation for each strategy plugin for details on how it works.
One example is ``debug`` strategy. See :doc:`playbooks_debugger` for details.
Setting the number of forks
---------------------------
If you have the processing power available and want to use more forks, you can set the number in ``ansible.cfg``::
[defaults]
forks = 30
or pass it on the command line: `ansible-playbook -f 30 my_playbook.yml`.
Using keywords to control execution
-----------------------------------
Several play-level :ref:`keyword<playbook_keywords>` also affect play execution. The most common one is ``serial``, which sets a number, a percentage, or a list of numbers of hosts you want to manage at a time. Setting ``serial`` with any strategy directs Ansible to 'batch' the hosts, completing the play on the specified number or percentage of hosts before starting the next 'batch'. This is especially useful for :ref:`rolling updates<rolling_update_batch_size>`.
Other keywords that affect play execution include ``ignore_errors``, ``ignore_unreachable``, and ``any_errors_fatal``. Please note that these keywords are not strategies. They are play-level directives or options.
.. seealso::
:doc:`playbooks`
:ref:`about_playbooks`
An introduction to playbooks
:doc:`playbooks_reuse_roles`
:ref:`playbooks_reuse_roles`
Playbook organization by roles
`User Mailing List <https://groups.google.com/group/ansible-devel>`_
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