What is Trunk Based Development? A Different Approach to the Software Development Lifecycle

The Software Development Lifecycle (SDLC) is the backbone of every software project, guiding the process from planning and design to deployment and maintenance. While the specific implementation of the SDLC varies across companies, there are some common approaches that have emerged over the years. One such approach is Trunk Based Development (TBD), which has gained popularity among tech giants like Google. In this article, we‘ll take a deep dive into TBD, exploring its strengths, weaknesses, and how it differs from other SDLC methodologies.

Understanding the Software Development Lifecycle

Before we delve into TBD, let‘s take a moment to understand the SDLC. The SDLC is a framework that defines the steps involved in developing and maintaining software. It typically includes the following phases:

1. Planning: Defining the project scope, objectives, and requirements
2. Design: Creating the software architecture and user interface
3. Development: Writing the actual code
4. Testing: Identifying and fixing bugs and ensuring the software meets the requirements
5. Deployment: Releasing the software to production
6. Maintenance: Providing ongoing support and updates

Each company has its own unique SDLC, tailored to its specific needs and constraints. Factors like the size of the development team, the complexity of the project, and the chosen development methodology (e.g., Agile, Waterfall) all influence how the SDLC is implemented.

What is Trunk Based Development?

Trunk Based Development is an SDLC approach that emphasizes frequent integration of code changes into a shared "trunk" or main branch. In TBD, developers work on small, incremental changes and merge their code into the trunk multiple times a day. This is in contrast to the more traditional feature branching approach, where developers work on separate branches for extended periods and only merge their changes once the feature is complete.

Here‘s a simplified example of how TBD works:

// Developer 1
git checkout main
git pull
// Make small code changes
git commit -m "Add login form validation"
git push

// Developer 2
git checkout main
git pull
// Make small code changes
git commit -m "Refactor user profile page"
git push

In this example, both developers are working directly on the main branch, making small, focused changes and pushing them to the shared repository frequently. This approach ensures that everyone is working with the latest code and reduces the risk of merge conflicts.

TBD at Scale: Lessons from Google

One of the most well-known adopters of TBD is Google. According to a talk by Rachel Potvin, an Engineering Manager at Google, one of their codebases had the following staggering stats as of January 2015:

• 1 billion files
• 2 billion lines of code
• 86 terabytes of content
• 45,000 commits per workday
• 15 million lines changed in 250,000 files per week

Despite the massive scale, Google has successfully employed TBD in this codebase. This is made possible by a combination of factors, including:

1. A highly skilled and experienced engineering team
2. A rigorous code review process
3. Extensive automated testing
4. Continuous integration and deployment pipelines

By embracing TBD, Google is able to deliver software quickly and efficiently, while maintaining a high level of quality and stability.

Strengths of Trunk Based Development

TBD offers several advantages over other SDLC approaches:

1. Quick feedback: With frequent integration, developers receive feedback on their changes quickly, allowing them to address issues and iterate faster.
2. Collaborative culture: TBD encourages a sense of shared ownership and collaboration, as everyone is working on the same codebase.
3. Early integration: By merging changes frequently, TBD catches integration issues early, reducing the risk of costly merge conflicts later on.
4. Modular code: TBD forces developers to break down large features into smaller, more manageable pieces, promoting modular and maintainable code.
5. Better monitoring: With everyone committing to the trunk regularly, it‘s easier to monitor progress and identify struggling team members.
6. Compatibility with continuous integration: TBD aligns well with continuous integration practices, ensuring a constantly tested and integrated codebase.

Here‘s an example of how TBD can lead to modular code:

// Feature: Add user authentication
// Instead of one large commit, break it down into smaller pieces

// Commit 1
git commit -m "Add user model and database migration"

// Commit 2
git commit -m "Implement user registration API endpoint"

// Commit 3
git commit -m "Create login form and authentication service"

// Commit 4
git commit -m "Add unit tests for user authentication"

By breaking down the user authentication feature into smaller, focused commits, the code becomes more modular and easier to review and maintain.

Weaknesses of Trunk Based Development

While TBD has many benefits, it‘s not without its challenges:

1. Risk of breaking the trunk: With frequent commits, there‘s an increased chance of introducing bugs that break the main branch.
2. Verbose commit history: TBD can lead to a more verbose and harder-to-follow commit history, making it challenging to track down issues.
3. Need for fast build process: To support frequent integration, TBD requires a fast and reliable build process.
4. Reliance on feature toggles: To manage the incremental development of features, TBD often relies on feature toggles, which can add complexity to the codebase.
5. Constant churn: With ongoing commits from multiple developers, TBD can create a sense of constant churn, requiring effective communication and coordination.

To mitigate these challenges, teams adopting TBD should invest in:

1. Robust automated testing
2. Efficient code review processes
3. Optimized build and deployment pipelines
4. Clear communication channels and collaboration tools

The TBD Release Process

In TBD, the release process differs from the feature branching approach. Instead of releasing from the main branch whenever a feature is merged, TBD teams typically use release branches to provide a stable snapshot of the codebase for deployment.

Here‘s a simplified example of the TBD release process:

// Create a release branch from the main branch
git checkout main
git checkout -b release-1.0

// Perform any necessary release preparations
// e.g., update version numbers, generate release notes

// Deploy the release branch to production
git push origin release-1.0

// If issues are found, fix them on the main branch and cherry-pick the commits to the release branch
git checkout main
git commit -m "Fix production issue"
git push

git checkout release-1.0
git cherry-pick <commit-hash>
git push

By using release branches, TBD teams can maintain a stable release while continuing to work on new features and bug fixes on the main branch.

Conclusion

Trunk Based Development offers a unique approach to the Software Development Lifecycle, emphasizing frequent integration, collaboration, and incremental development. While it has its challenges, TBD has proven to be effective at scale, as demonstrated by companies like Google.

If you‘re considering adopting TBD, it‘s essential to weigh its strengths and weaknesses against your team‘s specific needs and constraints. With the right tools, processes, and mindset, TBD can help you deliver high-quality software faster and more efficiently.

For more information on TBD, check out the Trunk Based Development website, which offers a wealth of resources on the theory and practice of this approach.

Remember, there‘s no one-size-fits-all solution when it comes to the SDLC. The key is to find the approach that works best for your team and continuously adapt and improve it over time.