VII. Contributing to cloud-init

Contributing to cloud-init project¶

Congratulations! You have journeyed from the fundamental concepts of cloud-init to advanced provisioning and troubleshooting techniques. You are now a cloud-init power user. This final chapter opens the door to the next step in your journey: moving from a consumer of cloud-init to a potential contributor.

cloud-init is a critical open-source project that thrives on community contributions. Whether it's fixing a typo in the documentation, reporting a bug, or writing a brand-new module, every contribution helps. This chapter provides a high-level map for understanding the source code, building a custom module, and engaging with the upstream community. It is not an exhaustive developer guide, but rather a friendly introduction to getting involved.

1. The `cloud-init` Source Code Landscape¶

Before you can contribute, you need to know your way around the project. Let's explore the source code and set up a basic development environment.

The Language and Repository¶

cloud-init is written almost entirely in Python. Its canonical source code repository is hosted on Launchpad, but for easier collaboration and a more familiar interface, most contributors interact with its official mirror on GitHub.

Canonical Repository (Launchpad): https://git.launchpad.net/cloud-init
GitHub Mirror: https://github.com/canonical/cloud-init

To get the source code, you can clone the GitHub repository:

# Clone the source code to your local machine
git clone https://github.com/canonical/cloud-init.git
cd cloud-init

Setting up a Development Environment¶

To work on the code without affecting your system's Python packages, you should always use a virtual environment.

# Create a Python virtual environment
python3 -m venv .venv

# Activate the virtual environment
source .venv/bin/activate

# Install the required development dependencies
pip install -r requirements-dev.txt

A High-Level Tour of the Source Code¶

Navigating a new codebase can be daunting. Here are the most important directories:

cloudinit/: This is the main Python source directory.
cloudinit/sources/: This directory contains the code for Datasources (e.g., DataSourceNoCloud.py). This is how cloud-init detects and reads configuration from different cloud platforms.
cloudinit/config/: This is where the Modules live (e.g., cc_packages.py, cc_users_groups.py). The cc_ prefix is a convention for modules that are enabled by #cloud-config. This is the most common place for new feature contributions.
doc/: The project's official documentation. Documentation improvements are one of the best ways to make your first contribution.
tests/: The comprehensive test suite for the project.

2. Writing a Basic Custom Module¶

While runcmd is useful, writing a proper module is the best way to create reusable, portable, and idempotent configurations.

Let's create the simplest possible module: one that reads a configuration key from user-data and writes a message to the cloud-init log.

Create the Module File: Create a new file named cloudinit/config/cc_hello_world.py.

# Filename: cloudinit/config/cc_hello_world.py

# A list of frequency and stage for this module to run
frequency = "once-per-instance"
distros = ["all"]

def handle(name, cfg, cloud, log, args):
    # Get a 'message' key from the user-data config.
    # If it doesn't exist, use a default value.
    message = cfg.get("message", "Hello from a custom module!")

    # Write the message to the main cloud-init log.
    log.info(f"Hello World Module says: {message}")

Enable the Module: Creating the file isn't enough. You must tell cloud-init to run it. Create a file at /etc/cloud/cloud.cfg.d/99-my-modules.cfg and add your module to one of the module lists:
```
# Add our custom module to the list of modules that run during the config stage
cloud_config_modules:
  - hello_world
```
Use the Module: Now, you can use the module in your user-data. The top-level key (hello_world) should match the module name without the cc_ prefix.
```
#cloud-config
hello_world:
  message: "My first custom module is working!"
```

After booting a VM with this configuration, you can check /var/log/cloud-init.log and you will find your custom message, proving your module worked.

3. The Contribution Workflow¶

Contributing to an open-source project follows a standard workflow. Here is a simplified overview:

Find Something to Work On: The best place to start is the project's issue tracker on Launchpad. Look for bugs or feature requests. Newcomers are encouraged to start with documentation fixes or issues tagged as "low-hanging-fruit" or "good first issue".
Fork and Branch: Create your own copy (a "fork") of the cloud-init repository on GitHub. Then, create a new branch for your changes.
```
git checkout -b my-documentation-fix
```
Make Your Changes and Commit: Make your code or documentation changes. When you commit, write a clear message describing what you did. The -s flag adds a Signed-off-by line, which certifies that you wrote the patch or have the right to contribute it.
```
git commit -s -m "Doc: Fix typo in the users module documentation"
```
Include Tests: All significant contributions, especially new features, are expected to include tests. Explore the tests/ directory to see how existing modules are tested.
Submit a Pull Request (PR): Push your branch to your fork on GitHub and open a Pull Request to the main branch of the canonical/cloud-init repository. This is your formal request to have your work included in the project.
Engage in Code Review: Project maintainers will review your PR. They may ask questions or request changes. This is a collaborative process. Engaging with feedback is a key part of contributing to open source.

Community Engagement¶

To learn more, ask questions, and interact with the community, you can join the #cloud-init channel on the OFTC IRC network or the official mailing list.

A Final Word¶

Congratulations on completing this guide. You have progressed from a novice user to a cloud-init power user, and now you have a map to guide you into the world of open-source contribution. The cloud-init community is welcoming, and your contributions, no matter how small, are valued. Happy building!

Author: Wale Soyinka