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Documentation

# Developing Plugins

Topics

- Developing Plugins
  - Callback Plugins
    - Example Callback Plugins
    - Configuring Callback Plugins
      - Managing stdout
    - Developing Callback Plugins
  - Connection Plugins
  - Lookup Plugins
  - Vars Plugins
  - Filter Plugins
  - Test Plugins
  - Distributing Plugins

Plugins are pieces of code that augment Ansible’s core functionality. Ansible ships with a number of handy plugins, and you can easily write your own.

The following types of plugins are available:

- Action plugins are front ends to modules and can execute actions on the controller before calling the modules themselves.
- Cache plugins are used to keep a cache of ‘facts’ to avoid costly fact-gathering operations.
- Callback plugins enable you to hook into Ansible events for display or logging purposes.
- Connection plugins define how to communicate with inventory hosts.
- Filters plugins allow you to manipulate data inside Ansible plays and/or templates. This is a Jinja2 feature; Ansible ships extra filter plugins.
- Lookup plugins are used to pull data from an external source. These are implemented using a custom Jinja2 function.
- Strategy plugins control the flow of a play and execution logic.
- Shell plugins deal with low-level commands and formatting for the different shells Ansible can encounter on remote hosts.
- Test plugins allow you to validate data inside Ansible plays and/or templates. This is a Jinja2 feature; Ansible ships extra test plugins.
- Vars plugins inject additional variable data into Ansible runs that did not come from an inventory, playbook, or the command line.

This section describes the various types of plugins and how to implement them.

## Callback Plugins

Callback plugins enable adding 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.

### Example Callback Plugins

Ansible comes with a number of callback plugins that you can look at for examples. These can be found in lib/ansible/plugins/callback.

The log_plays callback is an example of how to intercept playbook events to a log file, and the mail callback sends email when playbooks complete.

The osx_say callback provided is particularly entertaining – it will respond with computer synthesized speech on OS X in relation to playbook events, and is guaranteed to entertain and/or annoy coworkers.

### Configuring Callback Plugins

You can activate a custom callback by either dropping it into a callback_plugins directory adjacent to your play or inside a role or by putting it in one of the callback directory sources configured in ansible.cfg.

Plugins are loaded in alphanumeric order; for example, a plugin implemented in a file named 1_first.py would run before a plugin file named 2_second.py.

Most callbacks shipped with Ansible are disabled by default and need to be whitelisted in your ansible.cfg file in order to function. For example:

    #callback_whitelist = timer, mail, mycallbackplugin

#### Managing stdout

You can only have one plugin be the main manager of your console output. If you want to replace the default, you should define CALLBACK_TYPE = stdout in the subclass and then configure the stdout plugin in ansible.cfg. For example:

    #stdout_callback = mycallbackplugin

### Developing Callback Plugins

Callback plugins are created by creating a new class with the Base(Callbacks) class as the parent:

    from ansible.plugins.callback import CallbackBase
    from ansible import constants as C

    class CallbackModule(CallbackBase):
        pass

From there, override the specific methods from the CallbackBase that you want to provide a callback for. For plugins intended for use with Ansible version 2.0 and later, you should only override methods that start with v2. For a complete list of methods that you can override, please see `__init__.py` in the lib/ansible/plugins/callback directory.

The following example shows how Ansible’s timer plugin is implemented:

    # Make coding more python3-ish
    from __future__ import (absolute_import, division, print_function)
    __metaclass__ = type

    from datetime import datetime

    from ansible.plugins.callback import CallbackBase

    class CallbackModule(CallbackBase):
        """
        This callback module tells you how long your plays ran for.
        """
        CALLBACK_VERSION = 2.0
        CALLBACK_TYPE = 'aggregate'
        CALLBACK_NAME = 'timer'
        CALLBACK_NEEDS_WHITELIST = True

        def __init__(self):

            super(CallbackModule, self).__init__()

            self.start_time = datetime.now()

        def days_hours_minutes_seconds(self, runtime):
            minutes = (runtime.seconds // 60) % 60
            r_seconds = runtime.seconds - (minutes * 60)
            return runtime.days, runtime.seconds // 3600, minutes, r_seconds

        def playbook_on_stats(self, stats):
            self.v2_playbook_on_stats(stats)

        def v2_playbook_on_stats(self, stats):
            end_time = datetime.now()
            runtime = end_time - self.start_time
            self._display.display("Playbook run took %s days, %s hours, %s minutes, %s seconds" % (self.days_hours_minutes_seconds(runtime)))

Note that the CALLBACK_VERSION and CALLBACK_NAME definitions are required for properly functioning plugins for Ansible >=2.0.

## Connection Plugins

By default, Ansible ships with a ‘paramiko’ SSH, native ssh (just called ‘ssh’), ‘local’ connection type, and there are also some minor players like ‘chroot’ and ‘jail’. All of these can be used in playbooks and with /usr/bin/ansible to decide how you want to talk to remote machines. The basics of these connection types are covered in the Getting Started section. Should you want to extend Ansible to support other transports (SNMP, Message bus, etc) it’s as simple as copying the format of one of the existing modules and dropping it into the connection plugins directory. The value of ‘smart’ for a connection allows selection of paramiko or openssh based on system capabilities, and chooses ‘ssh’ if OpenSSH supports ControlPersist, in Ansible 1.2.1 and later. Previous versions did not support ‘smart’.

More documentation on writing connection plugins is pending, though you can jump into lib/ansible/plugins/connection and figure things out pretty easily.

## Lookup Plugins

Lookup plugins are used to pull in data from external data stores. Lookup plugins can be used within playbooks for both looping - playbook language constructs like “with_fileglob” and “with_items” are implemented via lookup plugins - and to return values into a variable or parameter.

Here’s a simple lookup plugin implementation - this lookup returns the contents of a text file as a variable:

    from ansible.errors import AnsibleError, AnsibleParserError
    from ansible.plugins.lookup import LookupBase

    try:
        from __main__ import display
    except ImportError:
        from ansible.utils.display import Display
        display = Display()

    class LookupModule(LookupBase):

        def run(self, terms, variables=None, **kwargs):

            ret = []

            for term in terms:
                display.debug("File lookup term: %s" % term)

                # Find the file in the expected search path
                lookupfile = self.find_file_in_search_path(variables, 'files', term)
                display.vvvv(u"File lookup using %s as file" % lookupfile)
                try:
                    if lookupfile:
                        contents, show_data = self._loader._get_file_contents(lookupfile)
                        ret.append(contents.rstrip())
                    else:
                        raise AnsibleParserError()
                except AnsibleParserError:
                    raise AnsibleError("could not locate file in lookup: %s" % term)

            return ret

An example of how this lookup is called:

    ---
    - hosts: all
      vars:
         contents: "{{ lookup('file', '/etc/foo.txt') }}"

      tasks:

         - debug: msg="the value of foo.txt is {{ contents }} as seen today {{ lookup('pipe', 'date +"%Y-%m-%d"') }}"

Errors encountered during execution should be returned by raising AnsibleError() with a message describing the error. Any strings returned by your lookup plugin implementation that could ever contain non-ASCII characters must be converted into Python’s unicode type because the strings will be run through jinja2. To do this, you can use:

    from ansible.module_utils._text import to_text
    result_string = to_text(result_string)

For more example lookup plugins, check out the source code for the lookup plugins that are included with Ansible here: lib/ansible/plugins/lookup.

For usage examples of lookup plugins, see Using Lookups.

## Vars Plugins

Playbook constructs like ‘host_vars’ and ‘group_vars’ work via ‘vars’ plugins. They inject additional variable data into ansible runs that did not come from an inventory, playbook, or command line. Note that variables can also be returned from inventory, so in most cases, you won’t need to write or understand vars_plugins.

More documentation on writing vars plugins is pending, though you can jump into lib/ansible/plugins and figure things out pretty easily.

If you find yourself wanting to write a vars_plugin, it’s more likely you should write an inventory script instead.

## Filter Plugins

Filter plugins are used for manipulating 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.

See lib/ansible/plugins/filter for details.

## Test Plugins

Test plugins are for verifying 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:.

See lib/ansible/plugins/test for details.

## Distributing Plugins

Plugins are loaded from the library installed path and the configured plugins directory (check your ansible.cfg). The location can vary depending on how you installed Ansible (pip, rpm, deb, etc) or by the OS/Distribution/Packager. Plugins are automatically loaded when you have one of the following subfolders adjacent to your playbook or inside a role:

> - action_plugins
> - lookup_plugins
> - callback_plugins
> - connection_plugins
> - filter_plugins
> - strategy_plugins
> - cache_plugins
> - test_plugins
> - shell_plugins

When shipped as part of a role, the plugin will be available as soon as the role is called in the play.

See also

About Modules
  List of built-in modules
Python API
  Learn about the Python API for task execution
Developing Dynamic Inventory Sources
  Learn about how to develop dynamic inventory sources
Developing Modules
  Learn about how to write Ansible modules
Mailing List
  The development mailing list
irc.freenode.net
  #ansible IRC chat channel