ansible/docsite/latest/rst/intro_inventory.rst

.. _patterns:

Inventory & Patterns
====================

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 being saved in 
the location /etc/ansible/hosts.

Not only is this inventory configurable, but you can also use
multiple inventory files at the same time (explained below) and also
pull inventory from dynamic or cloud sources, as described in `intro_inventory_dynamic`.

.. contents::
   :depth: 2

.. _inventoryformat:

Hosts and Groups
++++++++++++++++

The format for /etc/ansible/hosts is an INI format 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, which are used in classifying systems
and deciding what systems you are controlling at what times and for what purpose.

If you have hosts that run on non-standard SSH ports you can put the port number
after the hostname with a colon.  Ports listed in your SSH config file won't be used,
so it is important that you set them if things are not running on the default port::

    badwolf.example.com:5309

Suppose you have just static IPs and want to set up some aliases that don't live in your host file, or you are connecting through tunnels.  You can do things like this::

    jumper ansible_ssh_port=5555 ansible_ssh_host=192.168.1.50

In the above example, trying to ansible against the host alias "jumper" (which may not even be a real hostname) will contact 192.168.1.50 on port 5555.  Note that this is using a feature of the inventory file to define some special variables.  Generally speaking this is not the best
way to define variables that describe your system policy, but we'll share suggestions on doing this later.  We're just getting started.

Adding a lot of hosts?  If you have a lot of hosts following similar patterns you can do this rather than listing each hostname::


    [webservers]
    www[01:50].example.com

For numeric patterns, leading zeros can be included or removed, as desired. Ranges are inclusive.  You can also define alphabetic ranges::

    [databases]
    db-[a:f].example.com

You can also select the connection type and user on a per host basis::

   [targets]

   localhost              ansible_connection=local
   other1.example.com     ansible_connection=ssh        ansible_ssh_user=mpdehaan
   other2.example.com     ansible_connection=ssh        ansible_ssh_user=mdehaan

As mentioned above, setting these in the inventory file is only a shorthand, and we'll discuss how to store them in individual files
in the 'host_vars' directory a bit later on.

Host Variables
++++++++++++++

As alluded to above, 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
+++++++++++++++

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

Groups of Groups, and Group Variables
+++++++++++++++++++++++++++++++++++++

It is also 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]
   atlanta
   raleigh

   [southeast:vars]
   some_server=foo.southeast.example.com
   halon_system_timeout=30
   self_destruct_countdown=60
   escape_pods=2

   [usa:children]
   southeast
   northeast
   southwest
   southeast

If you need to store lists or hash data, or prefer to keep host and group specific variables
separate from the inventory file, see the next section.

Splitting Out Host and Group Specific Data
++++++++++++++++++++++++++++++++++++++++++

The preferred practice in Ansible is actually not to store variables in the main inventory file.

In addition to the storing variables directly in the INI file, host
and group variables can be stored in individual files relative to the
inventory file.  

These variable files are in YAML format.  See `YAMLSyntax` if you are new to YAML.

Assuming the inventory file path is::

    /etc/ansible/hosts

If the host is named 'foosball', and in groups 'raleigh' and 'webservers', variables
in YAML files at the following locations will be made available to the host::

    /etc/ansible/group_vars/raleigh
    /etc/ansible/group_vars/webservers
    /etc/ansible/host_vars/foosball

For instance, suppose you have hosts grouped by datacenter, and each datacenter
uses some different servers.  The data in the groupfile '/etc/ansible/group_vars/raleigh' for
the 'raleigh' group might look like::

    ---
    ntp_server: acme.example.org
    database_server: storage.example.org

It is ok if these files do not exist, as this is an optional feature.

Tip: In Ansible 1.2 or later the group_vars/ and host_vars/ directories can exist in either 
the playbook directory OR the inventory directory. If both paths exist, variables in the playbook
directory will be loaded second.

Tip: Keeping your inventory file and variables in a git repo (or other version control)
is an excellent way to track changes to your inventory and host variables.

List of Behavioral Inventory Parameters
+++++++++++++++++++++++++++++++++++++++

As aluded to above, setting the following variables controls how ansible interacts with remote hosts. Some we have already
mentioned::

ansible_ssh_host
  The name of the host to connect to, if different from the alias you wish to give to it.
ansible_ssh_port
  The ssh port number, if not 22
ansible_ssh_user
  The default ssh user name to use.
ansible_ssh_pass
  The ssh password to use (this is insecure, we strongly recommend using --ask-pass or SSH keys)
ansible_connection
  Connection type of the host. Candidates are local, ssh or paramiko.  The default is paramiko before Ansible 1.2, and 'smart' afterwards which detects whether usage of 'ssh' would be feasible based on whether ControlPersist is supported.
ansible_ssh_private_key_file
  Private key file used by ssh.  Useful if using multiple keys and you don't want to use SSH agent.
ansible_python_interpreter
  The target host python path. This is userful for systems with more
  than one Python or not located at "/usr/bin/python" such as \*BSD, or where /usr/bin/python
  is not a 2.X series Python.  We do not use the "/usr/bin/env" mechanism as that requires the remote user's
  path to be set right and also assumes the "python" executable is named python, where the executable might
  be named something like "python26".
ansible\_\*\_interpreter
  Works for anything such as ruby or perl and works just like ansible_python_interpreter.
  This replaces shebang of modules which will run on that host.

Examples from a host file::

  some_host         ansible_ssh_port=2222     ansible_ssh_user=manager
  aws_host          ansible_ssh_private_key_file=/home/example/.ssh/aws.pem
  freebsd_host      ansible_python_interpreter=/usr/local/bin/python
  ruby_module_host  ansible_ruby_interpreter=/usr/bin/ruby.1.9.3


.. seealso::

   :doc:`intro_inventory_dynamic`
       Pulling inventory from dynamic sources, such as cloud providers
   :doc:`intro_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