Using merge queues to achieve zero-downtime deployments

Zero-downtime deployments are essential in modern software development, ensuring updates occur smoothly without interrupting the end-user experience. Achieving a no-downtime release process demands careful management of code merges and deployments, particularly when deploying continuously.

Incorporating a merge queue into your continuous deployment strategy significantly enhances reliability and efficiency, preventing integration issues and enabling smooth, uninterrupted releases.

Understanding merge queues

Merge queues automatically coordinate and validate merges into the main codebase. By controlling how code changes enter production, merge queues prevent conflicting or unstable changes from disrupting the system. This approach facilitates a robust no-downtime release process.

Platforms such as Graphite offer streamlined merge queue implementation, integrating seamlessly with popular Git hosting services to simplify the adoption of zero-downtime deployments.

Benefits of merge queue implementation

• Improved stability: Merge queues ensure only verified changes are deployed, reducing deployment failures.
• Enhanced collaboration: Developers receive clear feedback on their changes, making team collaboration smoother.
• Continuous validation: Merge queues continuously test and validate code, reinforcing your continuous deployment strategy.

Implementing merge queues for zero-downtime deployments

Step 1: Configure your repository

Enable a merge queue within your Git hosting service (e.g., GitHub, GitLab) or integrate a specialized solution like Graphite. Configure branch protection rules to require merge queue checks before merging into critical branches (e.g., main or production).

Step 2: Automate your tests and checks

Set up automated tests and quality checks (unit tests, integration tests, end-to-end tests) triggered automatically by the merge queue for each proposed merge. This ensures only verified code passes through.

# Example CI pipeline triggered by a merge queue (GitHub Actions)
name: Merge Queue Validation

on:
  pull_request:
    types: [labeled]
    branches: [main]

jobs:
  validate-code:
    if: contains(github.event.pull_request.labels.*.name, 'merge-queue')
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Run tests
        run: |
          npm install
          npm test

Step 3: Deploy safely

Integrate merge queue approvals directly with your deployment pipeline. Deployments should trigger only after successful completion of merge queue validations.

# Example deployment snippet triggered post-validation
- name: Deploy application
  if: success()
  run: |
    ./deploy.sh production

Example workflow using Graphite

Graphite has its own merge queue, which enables developers to manage stacked changes and ensure smooth integration.

Here's a quick workflow overview:

1. Create your PR using Graphite.
2. Graphite automatically manages and visualizes the merge queue.
3. Automated tests run on each PR in the queue.
4. Graphite sequentially merges validated PRs into the main branch, ensuring zero-downtime deployments.

Best practices for a no-downtime release process

• Granular commits: Keep commits small and focused to simplify validation and troubleshooting.
• Fast feedback loops: Optimize your testing pipeline to provide rapid feedback.
• Rollback strategy: Always maintain a clear rollback procedure, allowing quick recovery from potential issues.

Conclusion

Integrating a merge queue into your continuous deployment strategy is crucial for achieving zero-downtime deployments. Solutions like Graphite significantly streamline this process, ensuring robust, reliable, and efficient software releases.