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ansible/docs/docsite/rst/dev_guide/developing_inventory.rst

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Developing Dynamic Inventory Sources
====================================
.. contents:: Topics
:local:
As described in :doc:`../intro_dynamic_inventory`, Ansible can pull inventory information from dynamic sources, including cloud sources. You can also create a new dynamic inventory provider by creating a script or program that can output JSON in the correct format when invoked with the proper arguments. There is no restriction on the language used for creating a dynamic inventory provider.
.. _inventory_script_conventions:
Script Conventions
``````````````````
Dynamic inventory providers must accept the ``--list`` and ``--host <hostname>`` arguments.
When the dynamic inventory provider is called with the single argument ``--list``, the script must output to stdout a JSON-encoded hash or dictionary containing all of the groups to be managed. Each group's value should be either a hash or dictionary containing a list of each host, any child groups, and potential group variables, or simply a list of hosts::
{
"group001": {
"hosts": ["host001", "" "host002"],
"vars": {
"var1": true
},
"children": ["group002"]
},
"group002": {
"hosts": ["host003","host004"],
"vars": {
"var2": 500
},
"children":[]
}
}
If any of the elements of a group are empty they may be omitted from the output.
When called with the argument ``--host <hostname>`` (where <hostname> is a host from above), the script must print either an empty JSON hash/dictionary, or a hash/dictionary of variables to make available to templates and playbooks. For example::
{
"VAR001": "VALUE",
"VAR002": "VALUE",
}
Printing variables is optional. If the inventory provider does not do this, it should print an empty hash or dictionary.
.. _inventory_script_tuning:
Tuning the External Inventory Script
````````````````````````````````````
.. versionadded:: 1.3
The stock inventory script system detailed above works for all versions of
Ansible, but calling ``--host`` for every host can be rather inefficient,
especially if it involves API calls to a remote subsystem. In Ansible 1.3 or
later, if the inventory script returns a top level element called "_meta", it
is possible to return all of the host variables in one inventory provider call.
When this meta element contains a value for "hostvars", the inventory script
will not be invoked with ``--host`` for each host. This results in a
significant performance increase for large numbers of hosts, and also makes
client-side caching easier to implement for the inventory provider.
The data to be added to the top level JSON dictionary looks like this::
{
# results of inventory script as above go here
# ...
"_meta": {
"hostvars": {
"host001": {
"var001" : "value"
},
"host002": {
"var002": "value"
}
}
}
}
To satisfy the requirements of using ``_meta``, to prevent ansible from calling your inventory with ``--host`` you must at least populate ``_meta`` with an empty ``hostvars`` dictionary. For example::
{
# results of inventory script as above go here
# ...
"_meta": {
"hostvars": {}
}
}
.. _replacing_inventory_ini_with_dynamic_provider:
If you intend to replace an existing inventory ini file with a dynamic provider,
it must return a JSON object which contains an 'all' group that includes every
host in the inventory as a member and every group in the inventory as a child.
It should also include an 'ungrouped' group which contains all hosts which are not members of
any other group. A skeleton example of this JSON object is::
{
"_meta": {
"hostvars": {}
},
"all": {
"children": [
"ungrouped"
]
},
"ungrouped": {}
}
.. seealso::
:doc:`developing_api`
Python API to Playbooks and Ad Hoc Task Execution
:doc:`developing_modules`
How to develop modules
:doc:`developing_plugins`
How to develop plugins
`Ansible Tower <https://ansible.com/ansible-tower>`_
REST API endpoint and GUI for Ansible, syncs with dynamic inventory
`Development Mailing List <http://groups.google.com/group/ansible-devel>`_
Mailing list for development topics
`irc.freenode.net <http://irc.freenode.net>`_
#ansible IRC chat channel