community.general/rst/api.rst

API & Integrations
==================

There are two major ways to use Ansible from an API perspective.   The primary way
is to use the Ansible python API to control nodes.  Ansible is written in it's own
API so you have a considerable amount of power there.  

Also covered here, Ansible's
list of hosts, groups, and variables assigned to each host can be driven from
external sources.   We'll start with the Python API.

Python API
----------

The Python API is very powerful, and is how the ansible CLI and ansible-playbook
are implemented.  

It's pretty simple::

    import ansible.runner

    runner = ansible.runner.Runner(
       module_name='ping',
       module_args='',
       pattern='web*',
       forks=10
    )
    datastructure = runner.run()

The run method returns results per host, grouped by whether they
could be contacted or not.  Return types are module specific, as
expressed in the 'ansible-modules' documentation.::

    {
        "dark" : {
           "web1.example.com" : "failure message"
        }
        "contacted" : {
           "web2.example.com" : 1
        }
    }

A module can return any type of JSON data it wants, so Ansible can
be used as a framework to rapidly build powerful applications and scripts.

Detailed API Example
````````````````````

The following script prints out the uptime information for all hosts::

    #!/usr/bin/python

    import ansible.runner
    import sys

    # construct the ansible runner and execute on all hosts
    results = ansible.runner.Runner(
        pattern='*', forks=10,
        module_name='command', module_args=['/usr/bin/uptime'],
    ).run()

    if results is None:
       print "No hosts found"
       sys.exit(1)

    print "UP ***********"
    for (hostname, result) in results['contacted'].items():
        if not 'failed' in result:
            print "%s >>> %s" % (hostname, result['stdout'])

    print "FAILED *******"
    for (hostname, result) in results['contacted'].items():
        if 'failed' in result:
            print "%s >>> %s" % (hostname, result['msg'])

    print "DOWN *********"
    for (hostname, result) in results['dark'].items():
        print "%s >>> %s" % (hostname, result)

Advanced programmers may also wish to read the source to ansible itself, for
it uses the Runner() API (with all available options) to implement the
command line tools ``ansible`` and ``ansible-playbook``.

External Inventory
------------------

Often a user of a configuration management system will want to keep inventory
in a different system.  Frequent examples include LDAP, `Cobbler <http://cobbler.github.com>`_, 
or a piece of expensive enterprisey CMDB software.   Ansible easily supports all
of these options via an external interventory system.  

If you have a data store system where an Ansible external inventory script doesn't already exist, this may require a little coding,J
but we have a `Cobbler example <https://github.com/ansible/ansible/blob/master/examples/scripts/cobbler_external_inventory.py>`_ in the main source tree -- but it's pretty simple, as we'll explain below -- that would provide a good starting point.  Like with modules, it's possible to build an external inventory script in any language, as long as it returns JSON.

If you are familiar with Puppet terminology, this concept is basically the same as 'external nodes', with the slight difference that it also defines which hosts are managed.


Script Conventions
++++++++++++++++++

When the external node script is called with no arguments, the script must return a JSON hash/dictionary of all the groups to be managed, with a list of each host/IP as the value for each hash/dictionary element, like so::

    {
        'databases'  : [ 'host1.example.com', 'host2.example.com' ],
        'webservers' : [ 'host2.example.com', 'host3.example.com' ],
        'atlanta'    : [ 'host1.example.com', 'host4.example.com', 'host5.example.com' ] 
    }

When called with a single argument, the name of a host from above, the script must return either an empty JSON
hash/dictionary, or a list of key/value variables to make available to templates.  Returning variables is optional,
if the script does not wish to do this, returning an empty hash/dictionary is the way to go::

    {
        'favcolor'   : 'red',
        'ntpserver'  : 'wolf.example.com',
        'monitoring' : 'pack.example.com'
    }

Example: The Cobbler External Inventory Script
++++++++++++++++++++++++++++++++++++++++++++++

It is expected that many Ansible users will also be `Cobbler <http://cobbler.github.com>`_ users.  Cobbler has a generic
layer that allows it to represent data for multiple configuration management systems (even at the same time), and has
been referred to as a 'lightweight CMDB' by some admins.   This particular script will communicate with Cobbler
using Cobbler's XMLRPC API.

To tie Ansible's inventory to Cobbler (optional), copy `this script <https://github.com/ansible/ansible/blob/master/examples/scripts/cobbler_external_inventory.py>` to /etc/ansible/hosts and `chmod +x` the file.  cobblerd will now need
to be running when you are using Ansible.

Test the file by running `./etc/ansible/hosts` directly.   You should see some JSON data output, but it may not have
anything in it just yet.

Let's explore what this does.  In cobbler, assume a scenario somewhat like the following::

    cobbler profile add --name=webserver --distro=CentOS6-x86_64
    cobbler profile edit --name=webserver --mgmt-classes="webserver" --ksmeta="a=2 b=3"
    cobbler system edit --name=foo --dns-name="foo.example.com" --mgmt-classes="atlanta" --ksmeta="c=4"
    cobbler system edit --name=bar --dns-name="bar.example.com" --mgmt-classes="atlanta" --ksmeta="c=5"

In the example above, the system 'foo.example.com' will be addressable by ansible directly, but will also be addressable when using the group names 'webserver' or 'atlanta'.  Since Ansible uses SSH, we'll try to contract system foo over 'foo.example.com', only, never just 'foo'.  Similarly, if you try "ansible foo" it wouldn't find the system... but "ansible 'foo*'" would, because the system DNS name starts with 'foo'.

The script doesn't just provide host and group info.  In addition, as a bonus, when the 'setup' module is run (which happens automatically when using playbooks), the variables 'a', 'b', and 'c' will all be auto-populated in the templates::

    # file: /srv/motd.j2
    Welcome, I am templated with a value of a={{ a }}, b={{ b }}, and c={{ c }}

Which could be executed just like this::

    ansible webserver -m setup
    ansible webserver -m template -a "src=/tmp/motd.j2 dest=/etc/motd"

Note that the name 'webserver' came from cobbler, as did the variables for the config file.  You can still
pass in your own variables like normal in Ansible, but variables from the external inventory script will
override any that have the same name.

So, with the template above (motd.j2), this would result in the following data being written to /etc/motd for system 'foo'::

    Welcome, I am templated with a value of a=2, b=3, and c=4

And on system 'bar' (bar.example.com)::

    Welcome, I am templated with a value of a=2, b=3, and c=5

And technically, though there is no major good reason to do it, this also works too::

    ansible webserver -m shell -a "echo {{ a }}"

So in other words, you can use those variables in arguments/actions as well.  You might use this to name
a conf.d file appropriately or something similar.  Who knows.

So that's the Cobbler integration support -- using the cobbler script as an example, it should be trivial to adapt Ansible to pull inventory, as well as variable information, from any data source.  If you create anything interesting, please share with the mailing list, and we can keep it in the source code tree for others to use.