Feature flags are used for gradual rollout and testing of features. Including, but not limited by, A/B tests, region-locking features, rolling to features to in

Feature flags are used for gradual rollout and testing of features. Including, but not limited by, A/B tests, region-locking features, rolling to features to internal users only and so on. For example, you're developing a new version of the checkout page for your company from scratch (it can be a store selling physical goods, or a subscription service, or anything that requires payment). It means that for a while it will not have feature parity with your existing checkout page. So first you implement feature parity with, say, German payment options (credit cards and Sofort). Then you set up a feature flag saying "for 5% of German customers display the new checkout", and monitor it. Then you bump it up to 10%, then to 50%. Meanwhile you're working on accepting payments via Swish in the new checkout in Sweden. Once it's ready, you add a feature flag saying "for 5% Swedish customers display the new checkout" (and in parallel, you're probably already displaying the new checkout to 50% German customers). And so on. In their core feature flags are not really more than a glorified if statement, but: - you want to view them, and handle them in a single place so that you can adjust the various parameters or quickly shut down a feature if it misbehaves - this single place has to be scalable enough that it survives an influx of customers potentially triggering dozens of feature flags across your software