ansible/patterns.html
2012-05-13 11:00:02 -04:00

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<li><a class="reference internal" href="#">Inventory &amp; Patterns</a><ul>
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<li><a class="reference internal" href="#selecting-targets">Selecting Targets</a></li>
<li><a class="reference internal" href="#host-variables">Host Variables</a></li>
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<div class="section" id="inventory-patterns">
<span id="patterns"></span><h1>Inventory &amp; Patterns<a class="headerlink" href="#inventory-patterns" title="Permalink to this headline"></a></h1>
<p>Ansible works against multiple systems in your infrastructure at the
same time. It does this by selecting portions of systems listed in
Ansible&#8217;s inventory file, which defaults to /etc/ansible/hosts.</p>
<div class="section" id="hosts-and-groups">
<span id="inventoryformat"></span><h2>Hosts and Groups<a class="headerlink" href="#hosts-and-groups" title="Permalink to this headline"></a></h2>
<p>The format for /etc/ansible/hosts is an INI format and looks like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">mail</span><span class="o">.</span><span class="n">example</span><span class="o">.</span><span class="n">com</span>
<span class="p">[</span><span class="n">webservers</span><span class="p">]</span>
<span class="n">foo</span><span class="o">.</span><span class="n">example</span><span class="o">.</span><span class="n">com</span>
<span class="n">bar</span><span class="o">.</span><span class="n">example</span><span class="o">.</span><span class="n">com</span>
<span class="p">[</span><span class="n">dbservers</span><span class="p">]</span>
<span class="n">one</span><span class="o">.</span><span class="n">example</span><span class="o">.</span><span class="n">com</span>
<span class="n">two</span><span class="o">.</span><span class="n">example</span><span class="o">.</span><span class="n">com</span>
<span class="n">three</span><span class="o">.</span><span class="n">example</span><span class="o">.</span><span class="n">com</span>
</pre></div>
</div>
<p>The things in brackets are group names. You don&#8217;t have to have them,
but they are useful.</p>
<p>If you have hosts that run on non-standard SSH ports you can put the port number
after the hostname with a colon.</p>
<blockquote>
<div>four.example.com:5309</div></blockquote>
</div>
<div class="section" id="selecting-targets">
<h2>Selecting Targets<a class="headerlink" href="#selecting-targets" title="Permalink to this headline"></a></h2>
<p>We&#8217;ll go over how to use the command line in <a class="reference internal" href="examples.html"><em>Command Line</em></a> section, however, basically it looks like this:</p>
<div class="highlight-python"><pre>ansible &lt;pattern_goes_here&gt; -m &lt;module_name&gt; -a &lt;arguments&gt;</pre>
</div>
<p>Such as:</p>
<div class="highlight-python"><pre>ansible webservers -m service -a "name=httpd state=restarted"</pre>
</div>
<p>Within <a class="reference internal" href="playbooks.html"><em>Playbooks</em></a>, these patterns can be used for even greater purposes.</p>
<p>Anyway, to use Ansible, you&#8217;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.</p>
<p>The following patterns target all hosts in the inventory file:</p>
<div class="highlight-python"><pre>all
*</pre>
</div>
<p>Basically &#8216;all&#8217; is an alias for &#8216;*&#8217;. It is also possible to address a specific host or hosts:</p>
<div class="highlight-python"><pre>one.example.com
one.example.com:two.example.com
192.168.1.50
192.168.1.*</pre>
</div>
<p>The following patterns address one or more groups, which are denoted
with the aforementioned bracket headers in the inventory file:</p>
<div class="highlight-python"><pre>webservers
webservers:dbservers</pre>
</div>
<p>Individual host names (or IPs), but not groups, can also be referenced using
wildcards:</p>
<div class="highlight-python"><pre>*.example.com
*.com</pre>
</div>
<p>It&#8217;s also ok to mix wildcard patterns and groups at the same time:</p>
<div class="highlight-python"><pre>one*.com:dbservers</pre>
</div>
<p>Easy enough. See <a class="reference internal" href="examples.html"><em>Command Line</em></a> and then <a class="reference internal" href="playbooks.html"><em>Playbooks</em></a> for how to do things to selected hosts.</p>
</div>
<div class="section" id="host-variables">
<h2>Host Variables<a class="headerlink" href="#host-variables" title="Permalink to this headline"></a></h2>
<p>Using the 0.4 branch of Ansible, it is easy to assign variables to hosts that will be used
later in playbooks:</p>
<div class="highlight-python"><pre>[atlanta]
host1 http_port=80 maxRequestsPerChild=808
host2 http_port=303 maxRequestsPerChild=909</pre>
</div>
</div>
<div class="section" id="group-variables">
<h2>Group Variables<a class="headerlink" href="#group-variables" title="Permalink to this headline"></a></h2>
<p>Using the 0.4 branch of Ansible, variables can also be applied to an entire group at once:</p>
<div class="highlight-python"><pre>[atlanta]
host1
host2
[atlanta:vars]
ntp_server=ntp.atlanta.example.com
proxy=proxy.atlanta.example.com</pre>
</div>
</div>
<div class="section" id="groups-of-groups-and-group-variables">
<h2>Groups of Groups, and Group Variables<a class="headerlink" href="#groups-of-groups-and-group-variables" title="Permalink to this headline"></a></h2>
<p>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.</p>
<blockquote>
<div><p>[atlanta]
host1
host2</p>
<p>[raleigh]
host2
host3</p>
<p>[southeast:children]
atlanta
raleigh</p>
<p>[southeast:vars]
some_server=foo.southeast.example.com
halon_system_timeout=30
self_destruct_countdown=60
escape_pods=2</p>
<p>[usa:children]
southeast
northeast
southwest
southeast</p>
</div></blockquote>
</div>
<div class="section" id="yaml-inventory-format">
<h2>YAML Inventory Format<a class="headerlink" href="#yaml-inventory-format" title="Permalink to this headline"></a></h2>
<p>For people using 0.3, or those that prefer to use it, the inventory file can also be expressed in
YAML:</p>
<div class="highlight-python"><pre>---
# 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</pre>
</div>
<p>Tip: Be sure to start your YAML file with the YAML record designator <tt class="docutils literal"><span class="pre">---</span></tt>.</p>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference internal" href="examples.html"><em>Command Line</em></a></dt>
<dd>Examples of basic commands</dd>
<dt><a class="reference internal" href="playbooks.html"><em>Playbooks</em></a></dt>
<dd>Learning ansible&#8217;s configuration management language</dd>
<dt><a class="reference external" href="http://groups.google.com/group/ansible-project">Mailing List</a></dt>
<dd>Questions? Help? Ideas? Stop by the list on Google Groups</dd>
<dt><a class="reference external" href="http://irc.freenode.net">irc.freenode.net</a></dt>
<dd>#ansible IRC chat channel</dd>
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&copy; Copyright 2012 Michael DeHaan.<br/>
Last updated on May 10, 2012.<br/>
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