ansible/rst/patterns.rst

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.. _patterns:
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Inventory & Patterns
====================
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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.
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.. _inventoryformat:
Hosts and Groups
++++++++++++++++
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The format for /etc/ansible/hosts is an INI format and looks like this::
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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.
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If you have hosts that run on non-standard SSH ports you can put the port number
after the hostname with a colon.
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four.example.com:5309
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Selecting Targets
+++++++++++++++++
We'll go over how to use the command line in :doc:`examples` section, however, basically it looks like this::
ansible <pattern_goes_here> -m <module_name> -a <arguments>
Such as::
ansible webservers -m service -a "name=httpd state=restarted"
Within :doc:`playbooks`, these patterns can be used for even greater purposes.
Anyway, to use Ansible, you'll first need to know how to tell Ansible which hosts in your inventory file to talk to.
This is done by designating particular host names or groups of hosts.
The following patterns target all hosts in the inventory file::
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all
*
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Basically 'all' is an alias for '*'. It is also possible to address a specific host or hosts::
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one.example.com
one.example.com:two.example.com
192.168.1.50
192.168.1.*
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The following patterns address one or more groups, which are denoted
with the aforementioned bracket headers in the inventory file::
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webservers
webservers:dbservers
Individual host names (or IPs), but not groups, can also be referenced using
wildcards::
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*.example.com
*.com
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It's also ok to mix wildcard patterns and groups at the same time::
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one*.com:dbservers
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Easy enough. See :doc:`examples` and then :doc:`playbooks` for how to do things to selected hosts.
Host Variables
++++++++++++++
Using the 0.4 branch of Ansible, it is easy to assign variables to hosts that will be used
later in playbooks::
[atlanta]
host1 http_port=80 maxRequestsPerChild=808
host2 http_port=303 maxRequestsPerChild=909
Group Variables
+++++++++++++++
Using the 0.4 branch of Ansible, variables can also be applied to an entire group at once::
[atlanta]
host1
host2
[atlanta:vars]
ntp_server=ntp.atlanta.example.com
proxy=proxy.atlanta.example.com
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Groups of Groups, and Group Variables
+++++++++++++++++++++++++++++++++++++
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Using Ansible 0.4, it is possible to make groups of groups and assign
variables to groups. These variables can be used by /usr/bin/ansible-playbook, but not
/usr/bin/ansible.
[atlanta]
host1
host2
[raleigh]
host2
host3
[southeast:children]
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atlanta
raleigh
[southeast:vars]
some_server=foo.southeast.example.com
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halon_system_timeout=30
self_destruct_countdown=60
escape_pods=2
[usa:children]
southeast
northeast
southwest
southeast
YAML Inventory Format
+++++++++++++++++++++
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For people using 0.3, or those that prefer to use it, the inventory file can also be expressed in
YAML::
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---
# some ungrouped hosts, either use the short string form or the "host: " prefix
- host: jupiter
- mars
# variables can be assigned like this...
- host: saturn
vars:
- moon: titan
# groups can also set variables to all hosts in the group
# here are a bunch of hosts using a non-standard SSH port
# and also defining a variable 'ntpserver'
- group: greek
hosts:
- zeus
- hera
- poseidon
vars:
- ansible_ssh_port: 3000
- ntp_server: olympus.example.com
# individual hosts can still set variables inside of groups too
# so you aren't limited to just group variables and host variables.
- group: norse
hosts:
- host: thor
vars:
- hammer: True
- odin
- loki
vars:
- asdf: 1234
Tip: Be sure to start your YAML file with the YAML record designator ``---``.
.. seealso::
:doc:`examples`
Examples of basic commands
:doc:`playbooks`
Learning ansible's configuration management language
`Mailing List <http://groups.google.com/group/ansible-project>`_
Questions? Help? Ideas? Stop by the list on Google Groups
`irc.freenode.net <http://irc.freenode.net>`_
#ansible IRC chat channel