Feature Flag Best Practices

Chapter 1. Introduction

Feature flags—also known as feature toggles, feature flippers, or feature bits—provide an opportunity for a radical change in the way software engineers deliver software products at a breakneck pace. Feature flags have a long history in software configuration but have since “crossed the chasm,” with growing adoption over the past few years as more and more engineering organizations are discovering that feature flags allow faster, safer delivery of features to their users by decoupling code deployment from feature release. Feature flags can be used for operational control, enabling “kill switches” that can dynamically reconfigure a live production system in response to high load or third-party outages. Feature flags also support continuous integration/continuous delivery (CI/CD) practices via simpler merges into the main software branch.

What’s more, feature flags enable a culture of continuous experimentation to determine what new features are actually desired by customers. For example, feature flags enable A/B/n testing, showing different experiences to different users and allowing for monitoring to see how those experiences affect their behavior.

In this book, we explain how to implement feature-flagged software successfully. We also offer some tips to developers on how to configure and manage a growing set of feature flags within your product, maintain them over time, manage infrastructure migrations, and more.