GitHub Actions How To Checkout And Build Two Different Repos In One Workflow

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In modern software development, managing multiple repositories and ensuring seamless integration between them is crucial. GitHub Actions provides a powerful platform for automating workflows, including checking out and building multiple repositories in a single workflow. This article will guide you through the process of setting up a GitHub Actions workflow that checks out two different repositories and triggers a build whenever changes occur in either of them. We'll explore the necessary steps, configurations, and best practices to achieve this efficiently.

Understanding the Need for Multi-Repo Workflows

Before diving into the technical details, let's understand why checking out and building multiple repositories in a single workflow is beneficial. In many projects, especially those following a microservices architecture or utilizing shared libraries, code is often spread across multiple repositories. A change in one repository might necessitate a build and test cycle in another dependent repository. Automating this process ensures that integrations are tested promptly and potential issues are identified early. By using a single workflow to manage multiple repositories, we can streamline the CI/CD process, reduce manual intervention, and maintain code integrity.

Setting Up the GitHub Actions Workflow

To begin, we need to create a new workflow file in our repository. This file will define the steps and configurations for our automated process. GitHub Actions workflows are defined using YAML syntax and are typically stored in the .github/workflows directory of your repository. Let's create a file named multi-repo-build.yml in this directory.

Step 1: Defining the Workflow Trigger

The first step is to define the trigger for our workflow. We want the workflow to run whenever there are changes in either of the two repositories. To achieve this, we can use the on keyword in our workflow file. The on keyword specifies the events that trigger the workflow. In our case, we want to trigger the workflow on push events for the main branch of both repositories. Here's how we can define the trigger:

name: Multi-Repo Build

on:
  push:
    branches:
      - main

This configuration tells GitHub Actions to run the workflow whenever there is a push to the main branch. However, this only applies to the repository where the workflow file is located. To monitor changes in another repository, we need to use the repository_dispatch event and set up a webhook in the second repository.

To monitor changes in another repository, we can use the repository_dispatch event. This event allows us to trigger a workflow in one repository from another repository. First, we need to set up a webhook in the second repository that listens for push events. This webhook will then send a repository_dispatch event to the first repository, triggering our workflow.

Here’s how we can modify the on section of our workflow file to include the repository_dispatch event:

on:
  push:
    branches:
      - main
  repository_dispatch:
    types:
      - repo_changed

In this configuration, the workflow will be triggered both by push events to the main branch and by repository_dispatch events with the type repo_changed. The next step is to set up the webhook in the second repository.

Step 2: Setting Up Webhooks in the Second Repository

To set up a webhook in the second repository, follow these steps:

  1. Go to the settings page of the second repository.
  2. Click on "Webhooks" in the sidebar.
  3. Click on "Add webhook".
  4. In the "Payload URL" field, enter the URL of your first repository’s repository_dispatch endpoint. This URL will look like this: https://api.github.com/repos/<your-username>/<your-first-repo>/dispatches.
  5. Set the "Content type" to application/json.
  6. In the "Secret" field, enter a secret token. This token will be used to verify that the webhook request is coming from the second repository. Make sure to store this secret securely, as we will need it later in our workflow.
  7. Select "Just the push event" in the "Which events would you like to trigger this webhook?" section.
  8. Click on "Add webhook".

Now that we have set up the webhook, we need to modify our workflow to send the repository_dispatch event when there is a push to the second repository. We can do this by adding a step to the workflow in the second repository that uses the GitHub API to trigger the repository_dispatch event in the first repository. Here’s an example of how we can do this:

name: Dispatch Repo Change

on:
  push:
    branches:
      - main

jobs:
  dispatch:
    runs-on: ubuntu-latest
    steps:
      - name: Dispatch Repository Event
        run: |
          curl -X POST \
            -H "Accept: application/vnd.github.v3+json" \
            -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" \
            --data '{"event_type": "repo_changed"}' \
            https://api.github.com/repos/<your-username>/<your-first-repo>/dispatches

In this workflow, we use the curl command to send a POST request to the repository_dispatch endpoint of the first repository. We include the event_type in the payload, which should match the type we specified in the on section of our first workflow (repo_changed). We also include the Authorization header with the GITHUB_TOKEN secret. This token is automatically provided by GitHub Actions and allows us to authenticate with the GitHub API. It is essential to ensure the GITHUB_TOKEN has the necessary permissions to trigger repository dispatches in the target repository. Without the correct permissions, the dispatch event will fail, and the workflow will not be triggered.

Step 3: Checking Out the Repositories

With the workflow trigger configured, the next step is to define the jobs and steps that will execute when the workflow runs. A job is a set of steps that run on the same runner, and steps are individual tasks that are executed in order. In our case, we need a job that checks out both repositories and performs the build. Let's define a job named build that runs on an Ubuntu runner:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout Repository 1
        uses: actions/checkout@v3
        with:
          repository: <your-username>/<repo-1>
          token: ${{ secrets.GITHUB_TOKEN }}
          path: repo-1

      - name: Checkout Repository 2
        uses: actions/checkout@v3
        with:
          repository: <your-username>/<repo-2>
          token: ${{ secrets.GITHUB_TOKEN }}
          path: repo-2

Here, we define a job named build that runs on the ubuntu-latest runner. We then define two steps that use the actions/checkout@v3 action to check out the repositories. The actions/checkout action is a standard action provided by GitHub that simplifies the process of checking out code. In the with section, we specify the repository to check out, the token to use for authentication, and the path where the repository should be checked out. The repository parameter specifies the full name of the repository, including the username or organization. The path parameter is crucial as it defines the local directory where the repository will be checked out within the runner’s file system. This allows you to have both repositories available simultaneously in the workflow environment.

We use the GITHUB_TOKEN secret for authentication, which is automatically provided by GitHub Actions. This token has sufficient permissions to check out code from the same repository where the workflow is running. If you need to check out code from a private repository, you may need to use a personal access token (PAT) with the appropriate permissions. Using a PAT involves creating the token in your GitHub settings and storing it as a secret in your repository settings. This secret can then be accessed in your workflow using the secrets context, similar to how GITHUB_TOKEN is used. However, exercise caution when using PATs, ensuring they have the minimum required permissions and are stored securely.

Step 4: Performing the Build

Now that we have checked out both repositories, we can perform the build. The build process will depend on the specific technologies and tools used in your projects. For example, if you are building a Node.js application, you might need to install dependencies and run build scripts. If you are building a Java application, you might need to compile the code and run tests. Let's add a step to our workflow that performs a simple build process for a Node.js application:

      - name: Set up Node.js
        uses: actions/setup-node@v3
        with:
          node-version: '16.x'

      - name: Install Dependencies
        run: npm install
        working-directory: ./repo-1

      - name: Build
        run: npm run build
        working-directory: ./repo-1

      - name: Test
        run: npm test
        working-directory: ./repo-1

In this example, we first set up Node.js using the actions/setup-node@v3 action. We then install dependencies, build the application, and run tests using npm commands. The working-directory parameter is essential here as it ensures that the commands are executed within the correct repository directory. Without specifying the working-directory, the commands would run in the root directory of the runner, leading to errors as the package.json and other necessary files would not be found.

Step 5: Adding Build Steps for the Second Repository

To perform builds for both repositories, you need to add similar steps for the second repository. These steps might include installing dependencies, running build scripts, and executing tests, depending on the project requirements. Here’s an example of how you can add these steps:

      - name: Install Dependencies (Repo 2)
        run: npm install
        working-directory: ./repo-2

      - name: Build (Repo 2)
        run: npm run build
        working-directory: ./repo-2

      - name: Test (Repo 2)
        run: npm test
        working-directory: ./repo-2

These steps are similar to the build steps for the first repository but are executed within the repo-2 directory. This ensures that the correct dependencies are installed and the appropriate build scripts are run for the second repository. Maintaining a consistent structure for build steps across different repositories enhances maintainability and reduces the likelihood of errors. Standardizing the build process makes it easier to troubleshoot issues and ensures that the builds are performed in a predictable manner.

Step 6: Complete Workflow File

Here is the complete workflow file that checks out two repositories and performs a build:

name: Multi-Repo Build

on:
  push:
    branches:
      - main
  repository_dispatch:
    types:
      - repo_changed

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout Repository 1
        uses: actions/checkout@v3
        with:
          repository: <your-username>/<repo-1>
          token: ${{ secrets.GITHUB_TOKEN }}
          path: repo-1

      - name: Checkout Repository 2
        uses: actions/checkout@v3
        with:
          repository: <your-username>/<repo-2>
          token: ${{ secrets.GITHUB_TOKEN }}
          path: repo-2

      - name: Set up Node.js
        uses: actions/setup-node@v3
        with:
          node-version: '16.x'

      - name: Install Dependencies (Repo 1)
        run: npm install
        working-directory: ./repo-1

      - name: Build (Repo 1)
        run: npm run build
        working-directory: ./repo-1

      - name: Test (Repo 1)
        run: npm test
        working-directory: ./repo-1

      - name: Install Dependencies (Repo 2)
        run: npm install
        working-directory: ./repo-2

      - name: Build (Repo 2)
        run: npm run build
        working-directory: ./repo-2

      - name: Test (Repo 2)
        run: npm test
        working-directory: ./repo-2

This workflow file defines a workflow named "Multi-Repo Build" that is triggered by push events to the main branch and repository_dispatch events of type repo_changed. The workflow consists of a single job named build that runs on an Ubuntu runner. The job checks out two repositories, sets up Node.js, installs dependencies, builds the applications, and runs tests for both repositories. This comprehensive example provides a solid foundation for building multi-repo workflows. You can adapt and extend this workflow to suit the specific needs of your projects, such as adding steps for deploying the applications or integrating with other services.

Best Practices and Considerations

When working with multi-repo workflows, there are several best practices and considerations to keep in mind:

  1. Use Secrets Wisely: Avoid hardcoding sensitive information in your workflow files. Use GitHub Secrets to store API keys, tokens, and other sensitive data.
  2. Minimize Dependencies: Keep the dependencies between repositories to a minimum. This will make your workflows more robust and easier to maintain.
  3. Optimize Build Times: Optimize your build process to minimize the time it takes to run. Use caching, parallel builds, and other techniques to improve performance.
  4. Monitor Workflow Runs: Regularly monitor your workflow runs to identify and address any issues. Use GitHub Actions insights and notifications to stay informed.
  5. Implement Proper Error Handling: Ensure your workflow handles errors gracefully. Use try...catch blocks and other error-handling mechanisms to prevent workflow failures.
  6. Secure Webhooks: When using webhooks, ensure they are properly secured. Use a secret token to verify that the webhook request is coming from a trusted source.

Conclusion

Checking out and building multiple repositories in a single GitHub Actions workflow can significantly streamline your CI/CD process. By following the steps outlined in this article, you can set up a robust and efficient workflow that automates the build process for multiple repositories. Remember to consider the best practices and considerations discussed to ensure your workflows are secure, maintainable, and performant. With GitHub Actions, managing complex multi-repo projects becomes more manageable, allowing you to focus on delivering high-quality software.

By implementing multi-repo workflows, you can ensure that changes in one repository are quickly and effectively integrated with other dependent repositories. This proactive approach to integration testing and continuous deployment significantly reduces the risk of integration issues and improves the overall quality of your software. Furthermore, the automation provided by GitHub Actions frees up developers to concentrate on writing code rather than managing build processes, leading to increased productivity and faster delivery cycles.