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116 lines
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ReStructuredText
116 lines
4 KiB
ReStructuredText
.. _intro_patterns:
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Working with Patterns
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=====================
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.. contents:: Topics
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Patterns in Ansible are how we decide which hosts to manage. This can mean what hosts to communicate with, but in terms
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of :doc:`playbooks` it actually means what hosts to apply a particular configuration or IT process to.
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We'll go over how to use the command line in :doc:`intro_adhoc` section, however, basically it looks like this::
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ansible <pattern_goes_here> -m <module_name> -a <arguments>
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Such as::
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ansible webservers -m service -a "name=httpd state=restarted"
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A pattern usually refers to a set of groups (which are sets of hosts) -- in the above case, machines in the "webservers" group.
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Anyway, to use Ansible, you'll first need to know how to tell Ansible which hosts in your inventory to talk to.
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This is done by designating particular host names or groups of hosts.
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The following patterns are equivalent and target all hosts in the inventory::
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all
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*
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It is also possible to address a specific host or set of hosts by name::
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one.example.com
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one.example.com:two.example.com
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192.0.2.50
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192.0.2.*
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The following patterns address one or more groups. Groups separated by a colon indicate an "OR" configuration.
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This means the host may be in either one group or the other::
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webservers
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webservers:dbservers
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You can exclude groups as well, for instance, all machines must be in the group webservers but not in the group phoenix::
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webservers:!phoenix
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You can also specify the intersection of two groups. This would mean the hosts must be in the group webservers and
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the host must also be in the group staging::
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webservers:&staging
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You can do combinations::
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webservers:dbservers:&staging:!phoenix
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The above configuration means "all machines in the groups 'webservers' and 'dbservers' are to be managed if they are in
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the group 'staging' also, but the machines are not to be managed if they are in the group 'phoenix' ... whew!
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You can also use variables if you want to pass some group specifiers via the "-e" argument to ansible-playbook, but this
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is uncommonly used::
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webservers:!{{excluded}}:&{{required}}
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You also don't have to manage by strictly defined groups. Individual host names, IPs and groups, can also be referenced using
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wildcards
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.. code-block:: none
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*.example.com
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*.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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You can select a host or subset of hosts from a group by their position. For example, given the following group::
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[webservers]
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cobweb
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webbing
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weber
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You can refer to hosts within the group by adding a subscript to the group name::
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webservers[0] # == cobweb
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webservers[-1] # == weber
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webservers[0:2] # == webservers[0],webservers[1]
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# == cobweb,webbing
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webservers[1:] # == webbing,weber
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webservers[:3] # == cobweb,webbing,weber
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Most people don't specify patterns as regular expressions, but you can. Just start the pattern with a '~'::
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~(web|db).*\.example\.com
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While we're jumping a bit ahead, additionally, you can add an exclusion criteria just by supplying the ``--limit`` flag to /usr/bin/ansible or /usr/bin/ansible-playbook::
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ansible-playbook site.yml --limit datacenter2
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And if you want to read the list of hosts from a file, prefix the file name with '@'.::
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ansible-playbook site.yml --limit @retry_hosts.txt
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Easy enough. See :doc:`intro_adhoc` and then :doc:`playbooks` for how to apply this knowledge.
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.. note:: You can use ',' instead of ':' as a host list separator. The ',' is preferred specially when dealing with ranges and ipv6.
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.. seealso::
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:doc:`intro_adhoc`
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Examples of basic commands
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:doc:`playbooks`
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Learning ansible's configuration management language
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`Mailing List <https://groups.google.com/group/ansible-project>`_
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Questions? Help? Ideas? Stop by the list on Google Groups
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`irc.freenode.net <http://irc.freenode.net>`_
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#ansible IRC chat channel
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