Trunk Based Development

Trunk based development consolidates work on a single main branch rather than maintaining multiple long-lived branches. All developers integrate their changes frequently to the shared trunk, keeping the codebase in a continuously releasable state. This approach simplifies branching while requiring strong practices around testing and feature management.

What Is Trunk Based Development

Trunk based development is a source control practice where all development happens on or integrates to a single branch called trunk or main. Short-lived feature branches may exist but merge back quickly, typically within a day or two. Long-lived branches for development or releases are avoided.

The approach contrasts with models like git flow that maintain multiple permanent branches. By reducing branch count and merge complexity, trunk based development simplifies workflows and enables faster integration.

How Trunk Based Development Works

Trunk based development relies on frequent integration, continuous testing, and feature management techniques. These practices enable working effectively without branch isolation.

Frequent integration means developers merge changes to trunk multiple times daily. Small, incremental commits reduce merge conflict likelihood and complexity. The trunk represents the latest integrated state of the system at all times.

Continuous testing validates every change against the full test suite. Automated tests run on commit and must pass before changes reach trunk. This catch-early approach prevents broken code from accumulating.

Feature management techniques handle incomplete work. Feature flags hide unfinished features from users while code lives in trunk. Branch by abstraction enables large changes through interface evolution rather than big-bang merges. These techniques enable trunk integration without exposing incomplete work.

Release process becomes simpler with trunk based development. Since trunk is always releasable, releases can happen at any time by tagging the current state. No release branch stabilization is needed because trunk is already stable.

Key Considerations

• Invest in comprehensive automated testing
• Keep changes small and integrate frequently
• Use feature flags to manage incomplete features
• Maintain trunk in always-releasable state
• Enable quick rollback for any release

Common Questions

How does trunk based development handle release stabilization?

Traditional release stabilization on dedicated branches is unnecessary when trunk is always releasable. However, some teams still want a stabilization period before major releases.

Release branches can exist briefly for final polish. Branching from trunk shortly before release, applying only critical fixes, and releasing quickly preserves most trunk based development benefits. The key is keeping these branches short-lived (days, not weeks).

Feature freeze periods achieve similar goals without branches. Stopping new feature integration while focusing on stability keeps work on trunk while controlling release content. This approach maintains branch simplicity.

For design systems, the always-releasable trunk philosophy aligns well with continuous or frequent releases. Major version releases with significant changes may benefit from brief stabilization periods using either technique.

What testing investment does trunk based development require?

Trunk based development requires comprehensive automated testing to maintain confidence in the always-releasable trunk. Without test coverage, trunk stability cannot be guaranteed.

Unit tests cover individual components in isolation. Integration tests verify component interactions. Visual regression tests catch unintended appearance changes. End-to-end tests validate complete user flows. This multi-layer testing provides confidence at different levels.

Test speed matters for frequent integration. Slow tests discourage frequent commits as developers wait for results. Optimizing test performance, parallelizing execution, and strategic test selection enable fast feedback loops.

The testing investment pays dividends beyond trunk based development. Comprehensive tests improve quality regardless of branching model. Trunk based development simply makes the investment essential rather than optional.

Summary

Trunk based development simplifies branching by consolidating work on a single main branch. Frequent integration, comprehensive testing, and feature management techniques enable this approach. Design systems benefit from the faster integration and simpler release processes trunk based development provides.