How merge queues streamline continuous deployment

A merge queue is a system that automates the process of integrating pull requests (PRs) into a main branch. It ensures that each PR is tested against the latest codebase and other queued changes before merging. This approach is particularly beneficial in continuous deployment (CD) environments, where maintaining a stable main branch is crucial for frequent releases.

Benefits of merge queues in continuous deployment

1. Automated merging process Merge queues automate the merging of PRs, reducing manual intervention. This automation ensures that only PRs that pass all required checks are merged, maintaining the integrity of the main branch.

2. Reduced merge conflicts By testing each PR against the latest version of the main branch and other queued PRs, merge queues minimize the likelihood of merge conflicts, leading to smoother integrations.

3. Consistent branch stability Merge queues help maintain a green main branch by ensuring that incompatible changes are identified and addressed before merging, preventing potential disruptions in the deployment pipeline.

4. Improved developer productivity Developers can focus on writing code without worrying about the intricacies of the merging process. Merge queues handle the complexities, allowing for a more streamlined workflow.

Key merge queue tools

• The Graphite Merge Queue: Graphite offers a stack-aware merge queue, allowing for faster concurrent merges and optimized PR ordering. It supports various merge strategies, including rebase, squash, and fast-forward merges. Graphite integrates seamlessly with GitHub, providing features like hot-fix prioritization and detailed merge activity tracking.

• GitHub's merge queue: GitHub's native merge queue automates PR merges into busy branches, ensuring that each PR is compatible with the latest codebase. It integrates with GitHub Actions or other CI providers to run required checks, enhancing the reliability of the merging process.

• Mergify: Mergify's merge queue automates the merging process, handling dependencies between PRs and resolving conflicts. It integrates with GitHub, allowing developers to define merge rules and automate workflows, leading to efficient and orderly merges.

Setting up the Graphite merge queue

To streamline your continuous deployment process with the Graphite Merge Queue, follow these steps:

1. Install the Graphite app Ensure your organization is on a Graphite Team or Enterprise plan. Then, install the Graphite App (GitHub app) on your organization.

2. Enable the merge queue for your repository In the Graphite app, navigate to the Merge Queue settings. Click Add merge queue, select your repository, and configure the desired settings.

3. Configure GitHub branch protection rules In your repository's GitHub settings, under Branches, edit the protection rules for your main branch:

   • Under Restrict who can push to matching branches, add graphite-app to the list of actors with push access.
   • Under Require a pull request before merging, enable Allow specified actors to bypass required pull requests and add graphite-app to the list.

4. Set merge queue preferences Choose your default merge strategy:

   • Rebase: Rebase changes on top of the trunk with commits unchanged.
   • Squash: Rebase changes on top of the trunk with each PR squashed into a single commit. Additionally, you can configure settings like timeouts and merge labels to control queue behavior.

5. Enqueue pull requests To add a PR to the queue:

   • Use the Queue option in the PR's merge modal within the Graphite app.
   • Alternatively, add a specified merge label (e.g., merge-when-ready) to the PR on GitHub.

6. Monitor and manage the merge queue Access the Merge activity page in the Graphite app to view queued PRs, their statuses, and manage the queue as needed.

By following these steps, you can effectively integrate Graphite's merge queue into your workflow, enhancing the efficiency and reliability of your continuous deployment pipeline.

Conclusion

Merge queues play a pivotal role in streamlining continuous deployment by automating the merging process, reducing conflicts, and maintaining branch stability. By integrating tools like Graphite, GitHub, or Mergify into your workflow, you can enhance the efficiency and reliability of your deployment pipeline.