What is a “feature flag”?

Question

High Scalability mentions feature flags here:

5 things toxic to scalability, \"5. Lack of Feature Flags\"

What exactly are feature flags?

Answer 1

Feature flags (or feature toggles) allow you to enable features remotely on an application without needing to re-build/re-deploy the application. This allows you to deploy the code to production but not release the feature until you are ready. You are able to target specific users, so you could enable a new feature to your beta users to test.

At our company we've previously used LaunchDarkly and other suggestions from FeatureFlags.io. We've also tried to use Firebase's Remote config to try and make this work however we found it wasn't really fit for this purpose.

We ended up developing our own version called Bullet Train, which we've open sourced. It combines both Feature Flags/Toggles and Remote Config.