Feature Flags

A feature flag is a conditional in the code that decides at runtime whether a particular behavior is on or off. The deployment ships the code; the flag turns the feature on.

This two-line idea has remade how modern teams ship software. Risky changes release to internal employees, then beta, then 1%, then 10%, then everyone, all without touching the deployment pipeline. Broken features turn off without a rollback. Different users see different behavior based on geography, account tier, or experiment cohort. Deploy and release become separate events.