Jonathan Lalou's blog

For many software development teams, managing feature branches in version control can be a source of significant pain and delays, particularly when branches diverge over long periods, leading to complex and time-consuming merge conflicts. Morgan LEROI proposed an alternative strategy: minimize or eliminate long-lived feature branches in favor of using Feature Toggles. His presentation explored the concepts behind feature toggles, their benefits, and shared practical experience on how this approach can streamline development workflows and enable new capabilities like activating features on demand.

Morgan opened by illustrating the common frustration associated with merging branches that have diverged significantly, describing it as a “traumatic experience”. This pain point underscores the need for development practices that reduce the time code spends in isolation before being integrated.

Embracing Feature Toggles

Feature Toggles, also known as Feature Flags, are a technique that allows developers to enable or disable specific features in an application at runtime, without deploying new code. The core idea is to merge code frequently into the main development branch (e.g., main or master), even if features are not yet complete or ready for production release. The incomplete or experimental features are wrapped in toggles that can be controlled externally.

Morgan explained that this approach addresses the merge hell problem by ensuring code is integrated continuously in small increments, minimizing divergence. It also decouples deployment from release; code containing new features can be deployed to production disabled, and the feature can be “released” or activated later via the toggle when ready.

Practical Benefits and Use Cases

Beyond simplifying merging, Feature Toggles offer several tangible benefits. Morgan highlighted their use by major industry players, including Amazon, demonstrating their effectiveness at scale. A key advantage is the ability to activate new features on demand, for specific user groups, or even for individual users. This enables phased rollouts, A/B testing, and easier rollback if a feature proves problematic.

Morgan detailed the application of feature toggles in A/B testing scenarios. By showing different versions of a feature (or the presence/absence of a feature) to different user segments, teams can collect metrics on user behavior and make data-driven decisions about which version is more effective. This allows for continuous experimentation and optimization based on real-world usage. He suggested that even a simple boolean configuration toggle (if (featureIsEnabled) { ... }) can be a starting point. Morgan encouraged developers to consider feature toggles as a powerful tool for improving development flow, reducing merge pain, and gaining flexibility in releasing new functionality. He challenged attendees to reflect on whether their current branching strategy is serving them well and to consider experimenting with feature toggles. Morgan Leroi is a Staff Software Engineer at Algolia.

Links:

• Morgan LEROI’s Twitter
• Morgan LEROI’s LinkedIn
• Morgan Leroi morganleroi – GitHub
• Tuez vos branches, faites des Feature Toggles (Morgan LEROI) – YouTube
• Video URL: https://www.youtube.com/watch?v=btrTtVWInc0

Hashtags: #FeatureToggles #BranchingStrategy #ContinuousDelivery #DevOps #SoftwareDevelopment #Agile #MorganLEROI #DevoxxFR2017