Trunk-Based Development (TBD) is a modern software development practice that aims to enhance productivity, streamline integration, and improve collaboration. It enables teams to work in parallel while continuously integrating their work, reducing the chances of conflicts and large-scale merge problems. Unlike traditional Git flow models with multiple long-lived branches, TBD advocates for a single, shared branch known as the "trunk" where all developers commit their code frequently.

In this article, we’ll dive into what Trunk-Based Development is, why it’s important, how it compares to other branching strategies, and its best practices.

What Is Trunk-Based Development?

Trunk-Based Development is a branching strategy where all developers commit their code to the mainline or “trunk” branch (often the master or main branch in Git). This encourages small, frequent updates rather than long-lived feature branches. Developers work on features in short-lived branches or directly on the trunk, merging their changes back to the trunk as soon as they’re ready.

This approach promotes continuous integration and enables faster feedback from automated tests and builds, which helps identify issues sooner in the development process.

Key Principles of Trunk-Based Development:

1. Single, Shared Trunk Branch: There is only one mainline branch, and all work eventually gets merged back to it. This makes integration easy and prevents the accumulation of large, out-of-sync changes.

2. Frequent Commits and Merges: Developers should commit to the trunk frequently (often multiple times per day). This ensures that work is continuously integrated, reducing integration issues.

3. Small, Incremental Changes: Rather than working on large features in isolation, TBD encourages small, incremental changes that can be merged into the trunk quickly. This keeps the trunk stable and always in a deployable state.

4. Feature Flags: To prevent incomplete features from disrupting the mainline code, TBD often uses feature flags (also known as feature toggles). These allow developers to hide unfinished features behind a flag while still committing their changes to the trunk.

5. Automated Testing and CI: Continuous Integration (CI) is a core part of TBD. Automated tests should run on every commit to the trunk, ensuring that all code integrated into the main branch is high-quality and doesn’t introduce regressions.

Benefits of Trunk-Based Development

1. Faster Feedback Loops
With frequent commits and automated testing, developers get rapid feedback on their changes. Any issues introduced into the codebase are caught early, making them easier to fix.

2. Reduced Merge Conflicts
Long-lived feature branches often result in large merge conflicts when they’re eventually integrated. TBD’s focus on small, frequent commits reduces the scope of conflicts, making merges smoother.

3. Simplified Version Control
In complex branching strategies like Git flow, managing multiple branches can become cumbersome, especially when they’re long-lived. With TBD, there’s no need to manage multiple branches over time, simplifying the development process.

4. Enhanced Collaboration
With everyone working on the same branch, TBD fosters closer collaboration. Developers are less likely to diverge from the shared codebase, and the team stays more in sync.

5. Consistent Release Cadence
TBD is ideal for continuous deployment. Because changes are committed frequently to a stable branch, the code is almost always in a deployable state. This consistency allows for quicker, more frequent releases, which is crucial in fast-paced environments like Agile or DevOps.

Best Practices for Trunk-Based Development

Use Short-Lived Branches: If you need to create a feature branch, keep it short-lived (no more than a few days). This helps prevent large merges and potential conflicts.

Enforce Code Reviews and Automated Testing: Use pull requests to ensure that code is reviewed before it’s merged into the trunk. This ensures high-quality code and minimizes errors.

Leverage Feature Flags: Incomplete or experimental features should be hidden behind feature flags. This allows developers to commit their changes without affecting the stability of the trunk.

Maintain a Deployable Trunk: The trunk should always be in a deployable state. Even if some features are incomplete, they shouldn’t break the build or cause issues in production.

Ensure Team Buy-In: Trunk-Based Development requires a shift in mindset for teams accustomed to long-lived feature branches. It’s essential to ensure the whole team is on board with the process.

When Should You Use Trunk-Based Development?

Trunk-Based Development is particularly well-suited for teams practicing continuous integration, continuous delivery, or DevOps. It’s also a good fit for teams that want to avoid the overhead of managing multiple long-lived branches.

However, teams that have a slower release cadence or work on highly complex features over extended periods might benefit more from other branching strategies like Git flow.

Conclusion

Trunk-Based Development is a modern, agile-friendly approach to version control. By focusing on continuous integration and frequent commits to a shared trunk, it encourages collaboration, reduces merge conflicts, and helps teams release high-quality code more quickly.

If your team is looking for a branching strategy that supports rapid iteration, continuous delivery, and streamlined development, Trunk-Based Development is worth considering.****