ansible/rst/patterns.rst

.. _patterns:

The Inventory File, Patterns, and Groups
========================================

How to select hosts you wish to manage

.. seealso::

   :doc:`examples`
       Examples of basic commands
   :doc:`playbooks`
       Learning ansible's configuration management language


.. _inventoryformat:

Inventory File Format
+++++++++++++++++++++

Ansible works against multiple systems in your infrastructure at the
same time.  It does this by selecting portions of systems listed in
Ansible's inventory file, which defaults to /etc/ansible/hosts, and
looks like this::

    mail.example.com

    [webservers]
    foo.example.com
    bar.example.com

    [dbservers]
    one.example.com
    two.example.com
    three.example.com

The things in brackets are group names, you don't have to have them,
but they are useful.

Selecting Targets
+++++++++++++++++

These patterns target all hosts in the inventory file::

    all
    *    

Basically 'all' is an alias for '*'.  It is also possible to address a specific host or hosts::

    one.example.com
    one.example.com:two.example.com
    192.168.1.50
    192.168.1.*
 
The following patterns address one or more groups, which are denoted
with the aforementioned bracket headers in the inventory file::

    webservers
    webservers:dbservers

Individual host names (or IPs), but not groups, can also be referenced using
wildcards::

    *.example.com
    *.com

It's also ok to mix wildcard patterns and groups at the same time::

    one*.com:dbservers

.. note::
    It is not possible to target a host not in the inventory file.   This is a safety feature.

Easy enough.  Now see :doc:`examples` and then :doc:`playbooks` for how to do things to selected hosts.