ansible/rst/modules.rst

Ansible Modules
===============

Ansible ships with a number of modules that can be executed directly on remote hosts or through
ansible playbooks.

.. seealso::

   :doc:`examples`
       Examples of using modules in /usr/bin/ansible
   :doc:`playbooks`
       Examples of using modules with /usr/bin/ansible-playbook
   :doc:`api`
       Examples of using modules with the Python API

Nearly all modules take key=value parameters.  Some modules take no parameters, and the command
module just takes arguments for the command you want to run.

All modules return JSON format data, thoug if you are using the command line or playbooks, you
don't really need to know much about that.

Most modules other than command are idempotent, meaning they will seek to avoid changes
unless a change needs to be made.  When using ansible playbooks, these modules can
trigger change events.  Unless otherwise noted, all modules support change hooks.

Stock modules:

command
```````

The command module takes the command name followed by a list of arguments, space delimited.
This is the only module that does not use key=value style parameters.

Example usage::

    /sbin/shutdown -t now

The given shell command will be executed on all selected nodes.

This module does not support change hooks and returns the return code from the program as well as timing information about how long the command was running for.


copy
````

The copy module moves a file on the local box to remote locations.  

*src*::

Local path to a file to copy to the remote server.  This can be an absolute or relative path.


*dest*::

Remote absolute path where the file should end up.


This module also returns md5sum information about the resultant file.


facter
``````

Runs the discovery program 'facter' on the remote system, returning
JSON data that can be useful for inventory purposes.  

Requires that 'facter' and 'ruby-json' be installed on the remote end.

This module is informative only - it takes no parameters & does not support change hooks,
nor does it make any changes on the system.   Playbooks do not actually use
this module, they use the 'setup' module behind the scenes.


git
```

Deploys software (or files) from git checkouts.

*repo*::

git or http protocol address of the repo to checkout

*dest*::

where to check it out, an absolute directory path

*version*::

what version to check out -- either the git SHA, the literal string 'HEAD', or a tag name


ohai
````

Similar to the facter module, this returns JSON inventory data.  Ohai
data is a bit more verbose and nested than facter.

Requires that 'ohai' be installed on the remote end.

This module is information only - it takes no parameters & does not
support change hooks, nor does it make any changes on the system.

Playbooks should not call the ohai module, playbooks call the 'setup'
module behind the scenes instead.

ping
````

A trivial test module, this module always returns the integer '1' on
successful contact.

This module does not support change hooks and is informative only - it takes no parameters & does not
support change hooks, nor does it make any changes on the system.


service
```````

Controls services on remote machines.

*state*

Values are 'started', 'stopped', or 'restarted'.   Started/stopped
are idempotent actions that will not run commands unless neccessary.
'restarted' will always bounce the service


*name*

The name of the service


setup
`````

Writes a JSON file containing key/value data, for use in templating.
Call this once before using the template modules.  Playbooks will
execute this module automatically as the first step in each play using
the variables section, so it is unneccessary to make explicit calls to
setup within a playbook.

If facter or ohai are installed, variables from these programs will also
be snapshotted into the JSON file for usage in templating. These variables
are prefixed with 'facter_' and 'ohai_" so it's easy to tell their source.
All variables are then bubbled up to the caller.

*anything*

any other parameters can be named basically anything, and set a key=value
pair in the JSON file for use in templating.


template
````````

Templates a file out to a remote server.  Call the setup module prior to usage.

*src*

path of a Jinja2 formatted template on the local server.  This can be a relative
or absolute path.

*dest*

location to render the template on the remote server


This module also returns md5sum information about the resultant file.


Writing your own modules
````````````````````````

To write your own modules, simply follow the convention of those already available in
/usr/share/ansible.  Modules must return JSON but can be written in any language.
Modules should return hashes, but hashes can be nested.

To support change hooks, modules should return hashes with a changed: True/False
element at the top level::

    {
        'changed'   : True,
        'something' : 42
    }

Modules can also choose to indicate a failure scenario by returning a top level 'failure' 
element with a True value, and a 'msg' element describing the nature of the failure.  
Other return values are up to the module.

    {
        'failure'   : True,
        'msg'       : "here is what happened..."
    }

When shipping modules, drop them in /usr/share/ansible, or specify the module path to the
command line tool or API.  It is easy to test modules by running them directly on
the command line, passing them arguments just like they would be passed with ansible.