Understanding Trunk-Based Development
Trunk-based development, often abbreviated TBD, is a branching strategy in which developers integrate their work into a single shared branch, usually called main or trunk, as often as possible. Branches, when used at all, live for hours rather than weeks, and are merged back before they can drift far from the trunk. This is the branching model that makes true Continuous Integration possible, since CI depends on frequent, small merges rather than occasional large ones.
How It Works
Developers either commit directly to trunk for small changes or open a short-lived branch that gets merged within a day. Work that is not ready to ship is hidden behind a feature flag rather than kept out of the codebase on a separate branch. Large or risky changes are broken down using techniques like branch by abstraction, where an old and new implementation coexist behind an interface until the new one is proven safe. This keeps the trunk always in a buildable, testable state, even while significant refactors are in progress.
Example
A team of eight engineers works on an e-commerce checkout flow. Instead of a long-lived feature branch for the new flow, each engineer commits directly to main several times a day, with the new checkout code hidden behind a flag called new-checkout-flow. Once the feature is complete and tested in production for a subset of users, the flag is flipped on for everyone and the old code path is deleted in a follow-up commit.
Trunk-Based Development vs. GitFlow
GitFlow relies on long-lived develop, feature, and release branches that can live for weeks, which works against continuous integration because the longer a branch lives, the more it diverges from trunk and the more painful the eventual merge becomes. Trunk-based development deliberately minimizes branch lifetime to avoid that divergence, trading the structure GitFlow provides for release management in exchange for constant integration and faster feedback.
Why Teams Use It
- It enables real Continuous Integration, since the whole point of CI is verifying small, frequent merges.
- Merge conflicts shrink dramatically because there is little time for code to diverge.
- Feedback on integration problems arrives within hours instead of at the end of a multi-week branch’s life.
- It pairs naturally with Continuous Deployment, since trunk is always close to a releasable state.
Trade-offs and Requirements
Trunk-based development requires discipline: developers must genuinely keep changes small and commit frequently, which is a cultural shift for teams used to isolating work on long branches. It depends on feature-flag infrastructure to hide incomplete work safely, and it can feel risky to teams without strong automated test coverage, since there is less isolation between in-progress and stable code. Teams new to CI culture sometimes need time to build the muscle of decomposing work into small, safely mergeable pieces.
Best Practices
- Keep branches alive for hours, not days, and merge as soon as a change is reviewed and passes CI.
- Use feature flags for anything not ready for all users, rather than keeping it off trunk.
- Enforce branch protection rules requiring passing CI checks and at least one review before merge.
- Invest in a fast, reliable automated test suite, since it is the primary safety net once branches stop providing isolation.
- Reserve dedicated release branches only for cutting hotfixes against an already-shipped version, not for ongoing feature work.
Frequently Asked Questions
What is Trunk-Based Development?
Trunk-based development is a source-control strategy where developers commit small changes directly to a single shared branch, using short-lived branches and feature flags instead of long-lived feature branches.
How does Trunk-Based Development work?
Trunk-Based Development works by combining the components described in the sections above. The main page walks through the architecture, the typical use cases, and the trade-offs to weigh before adopting it.
Why does Trunk-Based Development matter?
Teams adopt Trunk-Based Development to ship faster, run more reliably, and reduce the cognitive load on engineers. The benefits, limits, and adjacent tools are covered in the body above.
When should you use Trunk-Based Development?
Use Trunk-Based Development when the problems it solves match what your team is hitting today. The page above outlines the signals that mean you should adopt it now, and the cases where a simpler approach is fine.
