Streamlined Release Process for a Web Application: Trunk-Based Development with Feature Flags

In this article, we will outline a robust and efficient release process for web applications, built around trunk-based development and environment-based feature flags. This methodology ensures continuous integration, easy testing in production, and a smooth path from development to release while maintaining high-quality standards.

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Core Principles

1. Trunk-Based Development:

   • The trunk branch serves as the single source of truth for all development work.
   • Developers create feature branches (e.g., feature/xyz) from the trunk for new features or Jira tickets.
   • Pull requests (PRs) are submitted from these feature branches to the trunk for review and merging after successful tests.

2. Environment-Based Feature Flags:

   • Feature flags are used to control the activation of features across environments.
   • Flags are stored in environment-specific configuration files or as part of the CI/CD pipeline configuration.
   • In the trunk branch, all feature flags are set to OFF by default.
   • Flags can be toggled ON in specific environments (e.g., sandbox, staging, or production) as needed.

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JIRA Versions in Sprint

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Environment Deployment Flow

1. Sandbox or Staging Environment:

   • For QA and integration testing, teams can create a branch prefixed with sandbox/ (e.g., sandbox/xyz) from the trunk.
   • This branch is deployed to a dedicated sandbox or staging environment using CI/CD pipelines.
   • QA teams can validate new features, and integration tests can ensure compatibility.
   • Feature flags are toggled ON in this environment for testing specific features.

2. Production Release Preparation:

   • To prepare for a release, create a release/xyz branch from the trunk.
   • The release/xyz branch serves as the release candidate and is initially deployed to 5% of production traffic for beta testing.
   • Feature flags for new features are toggled ON in this branch to allow testing in production.
   • Nginx or a similar load balancer can handle this traffic split, ensuring only a subset of users see the changes.

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Feature Flags: Examples and Usage

1. Flag Structure:

   • Store feature flags in a configuration file (e.g., config/feature-flags.json):

    {
      "feature_xyz": false,
      "feature_abc": true
    }
   

• Use environment variables to control flags during runtime:
  

   FEATURE_XYZ=true FEATURE_ABC=false npm start
  

1. Backend Example:

   • Toggle flags in code:

    const featureFlags = require('./config/feature-flags');
   
    if (featureFlags.feature_xyz) {
        console.log('Feature XYZ is enabled!');
    } else {
        console.log('Feature XYZ is disabled.');
    }
   

2. Frontend Example:

   • Use flags to conditionally render UI components:

    if (process.env.REACT_APP_FEATURE_XYZ === 'true') {
        render(<NewFeatureComponent />);
    } else {
        render(<OldFeatureComponent />);
    }
   

3. Toggling Flags During Testing:

   • To toggle a flag for testing, update the configuration or environment variables and restart the relevant service (frontend or backend):

    FEATURE_XYZ=true npm start
   

• For CI/CD pipelines, ensure that the appropriate flag values are injected into the environment during deployment.

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Testing in Production

1. Traffic Routing for Beta Testing:

   • Use Nginx configurations to control traffic allocation:

    http {
        upstream stable_backend {
            server stable_backend_1;
            server stable_backend_2;
        }
   
        upstream canary_backend {
            server canary_backend_1;
            server canary_backend_2;
        }
   
        upstream mixed_backend {
            server stable_backend_1 weight=45;
            server stable_backend_2 weight=45;
            server canary_backend_1 weight=5;
            server canary_backend_2 weight=5;
        }
   
        server {
            listen 80;
            server_name my-app.example.com;
   
            location / {
                if ($http_x_qa_test = "true") {
                    proxy_pass http://canary_backend;
                    break;
                }
   
                proxy_pass http://mixed_backend;
            }
        }
    }
   

• Route 5% of production traffic to servers running the new version by adjusting load balancer weights.

1. Dedicated QA Testing in Production:
   • QA teams can attach a custom cookie (e.g., qa-test=true) to their requests.
   • Nginx checks this cookie and routes these requests to the new version 100% of the time, ensuring targeted testing in production.

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Stabilizing the Release

1. Fixing Issues:

   • Developers fix any issues identified during beta testing by opening PRs to the trunk branch.
   • Once merged, these fixes are cherry-picked into the release/xyz branch.

2. Finalizing the Release:

   • After all issues are resolved and the branch is stable, the release branch is tagged with a semantic version (e.g., v1.2.0), triggering deployment to the stable backend.
   • Release notes are generated for documentation and shared with stakeholders.

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Hotfix Process

1. Creating Hotfix Branches:

   • For urgent fixes, create a hotfix/xyz branch directly from the latest production tag.
   • Hotfix branches follow the same stabilization and tagging process as release branches.

2. Versioning:

   • Hotfixes increment the patch version (e.g., from v1.2.0 to v1.2.1) following Semantic Versioning (SemVer) standards.

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Branch Cleanup

• Routinely delete merged branches to avoid clutter.
• Periodically remove unused feature flags to maintain organization.
• Automate branch deletion post-merge using GitHub Actions or similar tools.

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Alternative QA and Testing Strategies

Instead of cookies, additional strategies for routing QA traffic in production include:

1. Header-Based Routing:

   • QA adds a custom header (e.g., X-QA-Test: true) to their requests.
   • Nginx routes these requests to the new version for testing.

2. IP-Based Routing:

   • Restrict traffic to the new version based on QA’s IP addresses.

3. Authentication Token-Based Routing:

   • QA logs in with a specific test account tied to a role or token that ensures requests are routed to the new version.

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Conclusion

This release process leverages trunk-based development and environment-based feature flags to create a scalable, testable, and production-safe deployment workflow. By using sandbox environments, traffic routing, and dedicated testing strategies, teams can deliver high-quality features while minimizing risk. The approach ensures that issues are caught early and addressed efficiently, paving the way for seamless feature rollouts and hotfixes.

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