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

My understanding is that feature flags help you gate functionality by deciding which users receive certain features.

For example, let's say you only want your beta users to see a new feature. You would "toggle" that feature on for beta users and the rest of your users would not see it.

LDUser user = new LDUser("user@test.com");

boolean showFeature = ldClient.toggle("your.feature.key", user, false);

if (showFeature) {
     // application code to show the feature 
 }
else {
     // the code to run if the feature is off
 }

I'm testing LaunchDarkly's feature flags for some front-end JS A/B tests - seems to be working well. You can also check out this site for feature toggles and feature flag libraries.