ansible/docs/docsite/rst/dev_guide/developing_modules_general.rst

Developing Ansible modules

A module is a reusable, standalone script that Ansible runs on your behalf, either locally or remotely. Modules interact with your local machine, an API, or a remote system to perform specific tasks like changing a database password or spinning up a cloud instance. Each module can be used by the Ansible API, or by the ansible or ansible-playbook programs. A module provides a defined interface, accepts arguments, and returns information to Ansible by printing a JSON string to stdout before exiting.

If you need functionality that is not available in any of the thousands of Ansible modules found in collections, you can easily write your own custom module. When you write a module for local use, you can choose any programming language and follow your own rules. Use this topic to learn how to create an Ansible module in Python. After you create a module, you must add it locally to the appropriate directory so that Ansible can find and execute it. For details about adding a module locally, see developing_locally.

Preparing an environment for developing Ansible modules

Installing prerequisites via apt (Ubuntu)

Due to dependencies (for example ansible -> paramiko -> pynacl -> libffi):

sudo apt update
sudo apt install build-essential libssl-dev libffi-dev python-dev

Installing prerequisites via yum (CentOS)

Due to dependencies (for example ansible -> paramiko -> pynacl -> libffi):

sudo yum check-update
sudo yum update
sudo yum group install "Development Tools"
sudo yum install python3-devel openssl-devel libffi libffi-devel 

Creating a development environment (platform-agnostic steps)

1. Clone the Ansible repository: $ git clone https://github.com/ansible/ansible.git
2. Change directory into the repository root dir: $ cd ansible
3. Create a virtual environment: $ python3 -m venv venv (or for Python 2 $ virtualenv venv. Note, this requires you to install the virtualenv package: $ pip install virtualenv)
4. Activate the virtual environment: $ . venv/bin/activate
5. Install development requirements: $ pip install -r requirements.txt
6. Run the environment setup script for each new dev shell process: $ . hacking/env-setup

Note

After the initial setup above, every time you are ready to start developing Ansible you should be able to just run the following from the root of the Ansible repo: $ . venv/bin/activate && . hacking/env-setup

Creating an info or a facts module

Ansible gathers information about the target machines using facts modules, and gathers information on other objects or files using info modules. If you find yourself trying to add state: info or state: list to an existing module, that is often a sign that a new dedicated _facts or _info module is needed.

In Ansible 2.8 and onwards, we have two type of information modules, they are *_info and *_facts.

If a module is named <something>_facts, it should be because its main purpose is returning ansible_facts. Do not name modules that do not do this with _facts. Only use ansible_facts for information that is specific to the host machine, for example network interfaces and their configuration, which operating system and which programs are installed.

Modules that query/return general information (and not ansible_facts) should be named _info. General information is non-host specific information, for example information on online/cloud services (you can access different accounts for the same online service from the same host), or information on VMs and containers accessible from the machine, or information on individual files or programs.

Info and facts modules, are just like any other Ansible Module, with a few minor requirements:

1. They MUST be named <something>_info or <something>_facts, where <something> is singular.
2. Info *_info modules MUST return in the form of the result dictionary<common_return_values> so other modules can access them.
3. Fact *_facts modules MUST return in the ansible_facts field of the result dictionary<common_return_values> so other modules can access them.
4. They MUST support check_mode <check_mode_dry>.
5. They MUST NOT make any changes to the system.
6. They MUST document the return fields<return_block> and examples<examples_block>.

To create an info module:

1. Navigate to the correct directory for your new module: $ cd lib/ansible/modules/. If you are developing module using collection, $ cd plugins/modules/ inside your collection development tree.
2. Create your new module file: $ touch my_test_info.py.
3. Paste the content below into your new info module file. It includes the required Ansible format and documentation <developing_modules_documenting>, a simple argument spec for declaring the module options <argument_spec>, and some example code.
4. Modify and extend the code to do what you want your new info module to do. See the programming tips <developing_modules_best_practices> and Python 3 compatibility <developing_python_3> pages for pointers on writing clean and concise module code.

../../../../examples/scripts/my_test_info.py

Use the same process to create a facts module.

../../../../examples/scripts/my_test_facts.py

Creating a module

To create a module:

1. Navigate to the correct directory for your new module: $ cd lib/ansible/modules/. If you are developing a module in a collection <developing_collections>, $ cd plugins/modules/ inside your collection development tree.
2. Create your new module file: $ touch my_test.py.
3. Paste the content below into your new module file. It includes the required Ansible format and documentation <developing_modules_documenting>, a simple argument spec for declaring the module options <argument_spec>, and some example code.
4. Modify and extend the code to do what you want your new module to do. See the programming tips <developing_modules_best_practices> and Python 3 compatibility <developing_python_3> pages for pointers on writing clean and concise module code.

../../../../examples/scripts/my_test.py

Verifying your module code

After you modify the sample code above to do what you want, you can try out your module. Our debugging tips <debugging_modules> will help if you run into bugs as you verify your module code.

Verifying your module code locally

If your module does not need to target a remote host, you can quickly and easily exercise your code locally like this:

• Create an arguments file, a basic JSON config file that passes parameters to your module so that you can run it. Name the arguments file /tmp/args.json and add the following content:

{
    "ANSIBLE_MODULE_ARGS": {
        "name": "hello",
        "new": true
    }
}

• If you are using a virtual environment (which is highly recommended for development) activate it: $ . venv/bin/activate
• Set up the environment for development: $ . hacking/env-setup
• Run your test module locally and directly: $ python -m ansible.modules.my_test /tmp/args.json

This should return output like this:

{"changed": true, "state": {"original_message": "hello", "new_message": "goodbye"}, "invocation": {"module_args": {"name": "hello", "new": true}}}

Verifying your module code in a playbook

The next step in verifying your new module is to consume it with an Ansible playbook.

• Create a playbook in any directory: $ touch testmod.yml

• Add the following to the new playbook file:

  - name: test my new module
    hosts: localhost
    tasks:
    - name: run the new module
      my_test:
        name: 'hello'
        new: true
      register: testout
    - name: dump test output
      debug:
        msg: '{{ testout }}'

• Run the playbook and analyze the output: $ ansible-playbook ./testmod.yml

Testing your newly-created module

The following two examples will get you started with testing your module code. Please review our testing <developing_testing> section for more detailed information, including instructions for testing module documentation <testing_module_documentation>, adding integration tests <testing_integration>, and more.

Note

Every new module and plugin should have integration tests, even if the tests cannot be run on Ansible CI infrastructure. In this case, the tests should be marked with the unsupported alias in aliases file.

Performing sanity tests

You can run through Ansible's sanity checks in a container:

$ ansible-test sanity -v --docker --python 2.7 MODULE_NAME

Note

Note that this example requires Docker to be installed and running. If you'd rather not use a container for this, you can choose to use --venv instead of --docker.

Adding unit tests

You can add unit tests for your module in ./test/units/modules. You must first set up your testing environment. In this example, we're using Python 3.5.

• Install the requirements (outside of your virtual environment): $ pip3 install -r ./test/lib/ansible_test/_data/requirements/units.txt
• Run . hacking/env-setup
• To run all tests do the following: $ ansible-test units --python 3.5. If you are using a CI environment, these tests will run automatically.

Note

Ansible uses pytest for unit testing.

To run pytest against a single test module, you can run the following command. Ensure that you are providing the correct path of the test module:

$ pytest -r a --cov=. --cov-report=html --fulltrace --color yes test/units/modules/.../test/my_test.py

Contributing back to Ansible

If you would like to contribute to ansible-core by adding a new feature or fixing a bug, create a fork of the ansible/ansible repository and develop against a new feature branch using the devel branch as a starting point. When you have a good working code change, you can submit a pull request to the Ansible repository by selecting your feature branch as a source and the Ansible devel branch as a target.

If you want to contribute a module to an Ansible collection <contributing_maintained_collections>, review our submission checklist <developing_modules_checklist>, programming tips <developing_modules_best_practices>, and strategy for maintaining Python 2 and Python 3 compatibility <developing_python_3>, as well as information about testing <developing_testing> before you open a pull request.

The Community Guide <ansible_community_guide> covers how to open a pull request and what happens next.

Communication and development support

Join the IRC channel #ansible-devel on irc.libera.chat for discussions surrounding Ansible development.

For questions and discussions pertaining to using the Ansible product, use the #ansible channel.

For more specific IRC channels look at Community Guide, Communicating <communication_irc>.

Credit

Thank you to Thomas Stringer (@trstringer) for contributing source material for this topic.