Learn the basics

This guide will help you understand the basic concepts of Lunar and get started with monitoring your engineering practices.

Prerequisites

Before you begin, make sure you have:

1. Installed Lunar following the installation guide

2. Access to your code repositories

3. Basic understanding of your CI/CD pipeline setup

Basic Concepts

Lunar operates on a few key concepts:

1. Components: These are your software projects (services, libraries, repositories)

2. Collectors: These gather information about your components

3. Policies: These define rules and standards for your components

4. Checks: These are the results of policy evaluations

Your First Lunar Setup

1. Populate your Lunar Configuration

Start by creating a lunar-config.yml file in your project root:

hub:
  host: <host>:<port>

# Use the official Lunar image for running scripts in containers
default_image: earthly/lunar-scripts:1.0.0

domains:
  team1:
    name: My Organization
    description: Main organization domain

components:
  github.com/my-org/my-service:
    owner: [email protected]
    domain: team1

collectors:
  - name: readme-lines
    runBash: |-
      if [ -f ./README.md ]; then
        lunar collect -j \
          "repo.readme_exists" true \
          "repo.readme_num_lines" "$(wc -l < ./README.md)"
      else
        lunar collect -j "repo.readme_exists" false
      fi
    hook:
      type: code

The default_image setting runs all collectors and policies inside Docker containers using the official earthly/lunar-scripts image. This image includes Python, Bash, the lunar CLI, and the lunar-policy package pre-installed. For more details on image configuration, see Images.

You will need to replace github.com/my-org/my-service with a real repository you want to monitor.

Note

Lunar can also auto-discover components from external systems like GitHub, Backstage, and other sources using catalogers. See the catalogers documentation for details on setting up automated component discovery. For now, this example will focus on manually declared components.

Commit this code to a new repository called lunar. To apply this configuration, run the following command:

lunar hub pull -r github.com://my-org/lunar@main

You should be able to see the new domain, the new component, and its component JSON being populated in the Lunar UI.

2. Define Your First Policy

Add a policy to check your component:

policies:
  - name: readme
    description: "README.md standards"
    on: ["domain:team1"]
    runPython: |-
      from lunar_policy import Check
      with Check("readme-exists", "Repository should have a README.md file") as c:
        c.assert_true(c.get(".repo.readme_exists"), "README.md file not found")

Since we're using the official earthly/lunar-scripts image (via default_image), the Lunar Policy SDK is already pre-installed—no requirements.txt needed.

Commit the code, and apply the new configuration:

lunar hub pull -r github.com://my-org/lunar@main

You should be able to see the new policy, and the checks being populated for this component in the Lunar UI.

Congratulations! You've just set up your first Lunar collector and policy.

See also

1. Learn more about key concepts

2. Explore configuration options

3. Install AI skills for Claude Code, Codex, or Cursor to help build collectors and policies