Plugins augment Ansible's core functionality with logic and features that are accessible to all modules. Ansible ships with a number of handy plugins, and you can easily write your own. All plugins must:
You must write your plugin in Python so it can be loaded by the ``PluginLoader`` and returned as a Python object that any module can use. Since your plugin will execute on the controller, you must write it in a :ref:`compatible version of Python <control_machine_requirements>`.
You should return errors encountered during plugin execution by raising ``AnsibleError()`` or a similar class with a message describing the error. When wrapping other exceptions into error messages, you should always use the ``to_text`` Ansible function to ensure proper string compatibility across Python versions:
Check the different `AnsibleError objects <https://github.com/ansible/ansible/blob/devel/lib/ansible/errors/__init__.py>`_ and see which one applies best to your situation.
You must convert any strings returned by your plugin into Python's unicode type. Converting to unicode ensures that these strings can run through Jinja2. To convert strings:
To define configurable options for your plugin, describe them in the ``DOCUMENTATION`` section of the python file. Callback and connection plugins have declared configuration requirements this way since Ansible version 2.4; most plugin types now do the same. This approach ensures that the documentation of your plugin's options will always be correct and up-to-date. To add a configurable option to your plugin, define it in this format:
To access the configuration settings in your plugin, use ``self.get_option(<option_name>)``. For most plugin types, the controller pre-populates the settings. If you need to populate settings explicitly, use a ``self.set_options()`` call.
Plugins that support embedded documentation (see :ref:`ansible-doc` for the list) must include well-formed doc strings to be considered for merge into the Ansible repo. If you inherit from a plugin, you must document the options it takes, either via a documentation fragment or as a copy. See :ref:`module_documenting` for more information on correct documentation. Thorough documentation is a good idea even if you're developing a plugin for local use.
Callback plugins add new behaviors to Ansible when responding to events. By default, callback plugins control most of the output you see when running the command line programs.
Note that the ``CALLBACK_VERSION`` and ``CALLBACK_NAME`` definitions are required for properly functioning plugins for Ansible version 2.0 and later. ``CALLBACK_TYPE`` is mostly needed to distinguish 'stdout' plugins from the rest, since you can only load one plugin that writes to stdout.
For example callback plugins, see the source code for the `callback plugins included with Ansible Core <https://github.com/ansible/ansible/tree/devel/lib/ansible/plugins/callback>`_
Connection plugins allow Ansible to connect to the target hosts so it can execute tasks on them. Ansible ships with many connection plugins, but only one can be used per host at a time. The most commonly used connection plugins are the ``paramiko`` SSH, native ssh (just called ``ssh``), and ``local`` connection types. All of these can be used in playbooks and with ``/usr/bin/ansible`` to connect to remote machines.
Ansible version 2.1 introduced the ``smart`` connection plugin. The ``smart`` connection type allows Ansible to automatically select either the ``paramiko`` or ``openssh`` connection plugin based on system capabilities, or the ``ssh`` connection plugin if OpenSSH supports ControlPersist.
To create a new connection plugin (for example, to support SNMP, Message bus, or other transports), copy the format of one of the existing connection plugins and drop it into the ``connection_plugins`` directory.
For example connection plugins, see the source code for the `connection plugins included with Ansible Core <https://github.com/ansible/ansible/tree/devel/lib/ansible/plugins/connection>`_.
Filter plugins manipulate data. They are a feature of Jinja2 and are also available in Jinja2 templates used by the ``template`` module. As with all plugins, they can be easily extended, but instead of having a file for each one you can have several per file. Most of the filter plugins shipped with Ansible reside in a ``core.py``.
Filter plugins do not use the standard configuration and documentation system described above.
For example filter plugins, see the source code for the `filter plugins included with Ansible Core <https://github.com/ansible/ansible/tree/devel/lib/ansible/plugins/filter>`_.
Lookup plugins pull in data from external data stores. Lookup plugins can be used within playbooks both for looping --- playbook language constructs like ``with_fileglob`` and ``with_items`` are implemented via lookup plugins --- and to return values into a variable or parameter.
Lookup plugins are very flexible, allowing you to retrieve and return any type of data. When writing lookup plugins, always return data of a consistent type that can be easily consumed in a playbook. Avoid parameters that change the returned data type. If there is a need to return a single value sometimes and a complex dictionary other times, write two different lookup plugins.
Ansible includes many :ref:`filters <playbooks_filters>` which can be used to manipulate the data returned by a lookup plugin. Sometimes it makes sense to do the filtering inside the lookup plugin, other times it is better to return results that can be filtered in the playbook. Keep in mind how the data will be referenced when determing the appropriate level of filtering to be done inside the lookup plugin.
For example lookup plugins, see the source code for the `lookup plugins included with Ansible Core <https://github.com/ansible/ansible/tree/devel/lib/ansible/plugins/lookup>`_.
Test plugins verify data. They are a feature of Jinja2 and are also available in Jinja2 templates used by the ``template`` module. As with all plugins, they can be easily extended, but instead of having a file for each one you can have several per file. Most of the test plugins shipped with Ansible reside in a ``core.py``. These are specially useful in conjunction with some filter plugins like ``map`` and ``select``; they are also available for conditional directives like ``when:``.
Test plugins do not use the standard configuration and documentation system described above.
For example test plugins, see the source code for the `test plugins included with Ansible Core <https://github.com/ansible/ansible/tree/devel/lib/ansible/plugins/test>`_.
Vars plugins inject additional variable data into Ansible runs that did not come from an inventory source, playbook, or command line. Playbook constructs like 'host_vars' and 'group_vars' work using vars plugins.
* path: this is 'directory data' for every inventory source and the current play's playbook directory, so they can search for data in reference to them. ``get_vars`` will be called at least once per available path.
Since Ansible version 2.4, vars plugins only execute as needed when preparing to execute a task. This avoids the costly 'always execute' behavior that occurred during inventory construction in older versions of Ansible.
