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

At my company we use feature flags for every new feature we introduce in our SaaS app. Apart from the benefits to performance it also allows us to roll out new features gradually - introducing new features to power users first, getting feedback from them and improvising it before we can roll it out to all users.

It also allows us to customize offering to individual users - power users want all features; simple users may just want the basic stuff and may get confused by all the powerful complex features. It also allows our sales team to up-sell.

And of course as others have pointed out, if we find a feature is causing a performance degradation, we can simply turn off that one feature (either for all clients or for the one client who is causing an issue).