Explaining Trunk Based Development
Trunk-Based Development (TBD) is a branching model where developers collaborate on a single branch—typically called ‘trunk’ or ‘main’—making small, frequent commits. It relies on Continuous Integration (CI) to automate testing and deployment, helping teams deliver faster and avoid integration issues. Unlike traditional models with long-lived branches, TBD keeps the codebase continuously releasable. This article explores TBD, its benefits, best practices, challenges, and how tools like ConfigCat enable safer feature releases through feature flags.
What Is Trunk Based Development?
Trunk Based Development is a source code management strategy where developers work on a single branch, the ‘trunk’, rather than working on multiple long-lived feature branches. The core principles of TBD include:
Single Branch Philosophy: All code changes are integrated into the trunk, ensuring everyone works with the latest version. Each code change should be small and manageable to maintain a streamlined and deploy-ready codebase.
Frequent Commits: Developers commit changes to the trunk at least once per day, reducing the risk of large, disruptive merges.
Small, Incremental Changes: Work is broken down into small, manageable pieces, making it easier to review, test, and integrate.
Continuously Releasable Codebase: The trunk is always kept in a deployable state, enabling rapid releases and continuous delivery.
In trunk-based development, teams may use short-lived branches or commit directly to the trunk, aiming to reduce code divergence and increase integration. Branches are merged at least daily to support steady releases and agile progress.
Trunk Based Development vs. Traditional Branching Models
Trunk Based Development vs. GitFlow
GitFlow is a popular branching model that uses multiple long-lived branches:
The master branch holds production-ready code and represents the official release history.
The develop branch is used as an integration branch for features and represents the latest delivered development changes for the next release.
Feature branches are created off of develop to work on new features or improvements. Once complete, they are merged back into develop.
Release branches are created from develop when a set of features is ready for release. This allows final testing and bug fixes without disturbing ongoing development.
Hotfix branches are created from master to quickly patch production issues. Once fixed, changes are merged into both master and develop to keep everything in sync.
Branching Structure: GitFlow’s multiple branches can lead to complex merges and delayed integration. TBD’s single branch reduces complexity and encourages early integration.
Release Cadence: GitFlow typically supports scheduled releases, while TBD enables continuous delivery.
Team Coordination: GitFlow can be more suitable for larger teams with strict release cycles, but it increases merge conflicts and integration challenges. TBD is designed to streamline collaboration and reduce these issues, making it ideal for teams that need to move quickly and keep the codebase always ready to release.
Trunk Based Development vs. GitHub Flow and Other Models
GitHub Flow is a simplified branching strategy where developers create feature branches off main, open pull requests, and merge changes after review. While similar to TBD in its focus on simplicity, GitHub Flow often allows longer-lived feature branches than strict TBD.
Feature branching is another development strategy where developers work on separate branches for an extended period, often weeks or months, until their features are complete. This approach contrasts with trunk-based development, highlighting the challenges of merging and the potential for lengthy code reviews due to multiple changes in the main branch during the development cycle.
In GitHub Flow, there are no dedicated release branches like in GitFlow. Instead, all development is done in short-lived feature branches created from the main branch. Once a feature is complete and reviewed through a pull request, it is merged back into main, which is always kept in a deployable state. Releases are typically made directly from the main branch.
Integration Frequency: TBD enforces more frequent integration, minimizing the risk of integration hell.
Branch Lifespan: GitHub Flow’s long lived feature branches may persist longer, increasing the risk of merge conflicts.
Hybrid Approaches: GitLab Flow and other models attempt to blend aspects of both, but TBD remains the most streamlined for continuous integration and delivery.
Benefits of Trunk Based Development
Reduced Merging Complexity
TBD virtually eliminates “merge hell” by encouraging small, frequent integrations. Integration tests play a crucial role in maintaining code quality and facilitating continuous integration by ensuring that code changes can be merged smoothly without introducing new issues. With everyone working on the same branch, conflicts are identified and resolved quickly, reducing the time and effort spent on complex merges.
Improved Team Collaboration
Working on a single main branch makes it easier to see what everyone is doing and encourages shared ownership of the code. Managing commits and maintaining software quality can be challenging for many developers, especially in larger teams, but trunk-based development offers robust systems to address these issues.
Faster Development Cycles
TBD accelerates feedback loops and reduces waiting times for integration, enabling teams to deliver features and fixes more rapidly. Testing in a production environment ensures that code changes can be safely deployed, reducing the risk of potential bugs. The continuous flow of changes to production shortens the time-to-market and allows for more frequent releases.
Better Quality and Stability
Smaller changes are easier to review and test, leading to higher code quality. Maintaining a production-ready codebase is essential to minimize risks associated with faulty code that could disrupt the entire build process. Automated testing and continuous integration catch issues early, ensuring the trunk remains stable and deployable at all times.
Implementing Trunk Based Development
For Small Teams
Small teams often commit directly to the trunk, leveraging pair programming and lightweight code reviews to maintain quality. To ensure stability and reliability, it is crucial that features are complete and thoroughly tested before integration. Communication is key, and developers are encouraged to test locally before pushing changes. This approach minimizes overhead and maximizes agility.
For Scaled Organizations
Larger organizations may use short-lived feature branches (lasting less than a day) and pull request workflows to manage contributions. Frequent updates in trunk-based development streamline integration phases, ensuring a smooth release pipeline. Techniques like “branch by abstraction” and feature flags help manage incomplete features without long-lived active branches.
Essential Tools and Infrastructure for Implementing TBD
Version Control Systems: Tools like Git or Mercurial version control, configured for a single-branch workflow.
CI/CD Pipelines: Automated build, test, and deployment pipelines to ensure the trunk remains stable.
Feature Management: Implement feature flags to control the release and visibility of new features without affecting the main codebase. Tools like ConfigCat make this easier by offering feature flagging and configuration management, which enable trunk-based development.
Automated Testing Frameworks: Comprehensive unit, integration, and end-to-end tests.
Monitoring and Alerting: Systems to detect and address build failures quickly.
Best Practices for Trunk Based Development
Commit Frequency and Size
Developers should commit at least once per day, breaking work into small, manageable pieces. Managing these distinct copies of the codebase, called branches, effectively is crucial to avoid complications. This reduces integration risk and makes code reviews more effective. Avoid large, sweeping changes that are hard to test and review.
Pre-Integration Verification
Before committing, developers should build and test code locally, run linters, and perform static analysis. The development team plays a crucial role in ensuring that only high-quality code reaches the trunk and prevents broken builds.
Comprehensive Testing Strategy
Automated tests are critical in TBD. Maintain high test coverage with unit, integration, and end-to-end tests. Test-driven development (TDD) can further improve maintainability and confidence.
Effective Code Reviews
Quick and regular code reviews help find problems early and share knowledge.
Feature Flags in Trunk Based Development
One challenge in TBD is managing and integrating incomplete features without disrupting the main codebase. Effective collaboration among other developers is crucial in managing these incomplete features, as it helps in coordinating overlapping code contributions. Teams can use feature flags and branch by abstraction to hide unfinished work and coordinate development across multiple contributors.
What Are Feature Flags?
Feature flags, also known as feature toggles, are a technique for enabling or disabling features in a codebase without deploying new code. This approach significantly enhances the end user experience by allowing engineering teams to have more control and flexibility in delivering software. They allow teams to merge incomplete features into trunk, hide them from users, and gradually roll them out when ready.
Benefits of Feature Flags with Trunk Based Development
Faster and Safer Development: Trunk Based Development combined with feature flags is far more efficient than traditional feature branching, which often requires days or weeks of coordination and merging. Developers can integrate code into the main branch early and often, reducing integration headaches and speeding up delivery.
Separation of Deployment from Release: Features can be merged and deployed without being visible to users.
Risk Reduction: Teams can test new features in production, roll them out gradually, and quickly disable them if issues arise.
A/B Testing and Experimentation: Experiment with different implementations and gather real-world user feedback, analyze results, and make data-driven decisions to improve the product.
Emergency Kill Switches: Instantly disable problematic features without rolling back code.
Improved Collaboration: Feature flags support better collaboration between development, QA, product, and operations teams. Features can be tested independently and released when the business is ready, not just when development is finished.
ConfigCat: Feature Flag Management for Trunk Based Development
ConfigCat is a robust feature flag service that integrates seamlessly with Trunk Based Development workflows. It allows teams to manage feature flags, set targeting rules, perform percentage rollouts, and run A/B tests—all from a user-friendly dashboard. Opensource ConfigCat’s SDKs make it easy to implement feature flags in any application, enabling teams to merge code confidently and deliver features safely.
Conclusion: Is Trunk Based Development Right for Your Team?
Adopting trunk-based development begins with a mindset shift. Teams need to embrace the practice of working with short-lived branches, encouraging smaller, more frequent pull requests, faster code reviews, and earlier integrations.
This cultural change is best supported by the right tooling. Long-lived branches typically persist for two main reasons—either the team lacks confidence in the code, or the code isn’t ready for release. Both issues can be addressed with proper tools and practices.
Robust testing and a solid CI/CD pipeline build confidence in every merge, reducing the risk of regressions and improving quality.
Feature flags, on the other hand, allow code to be merged without being immediately released, decoupling deployment from release and giving teams greater flexibility.
Ultimately, the combination of a new development mindset and supportive tools can successfully guide your team toward trunk based development. It enables faster shipping and leads to better, more successful products.
If you are looking for a robust feature flagging solution, ConfigCat is well-equipped to meet your needs.
