featureFlags

Feature flags, or feature toggles, are a software technique that gates functionality behind configurable flags. They allow code to be deployed with a feature disabled and enabled later at runtime, decoupling release from deployment.

Flags can be boolean (on or off) or multivariate (different variations selected by user, traffic percentage, or environment). They may be implemented in code or managed by an external flag service, and they follow a lifecycle of creation, activation, evaluation, and retirement.

Common patterns include release toggles for gradual exposure, experimentation toggles for A/B tests, and operations toggles to enable quick shutdown during failures. Benefits include safer deployments, faster feedback, and the ability to roll back without new deployments.

Risks include flag proliferation, technical debt if flags are forgotten, and added complexity. Mitigations include keeping flags temporary, assigning owners, documenting purposes, automating cleanup, and using a centralized flag management system.

Implementation considerations involve safe default states, separating flag evaluation from business logic, monitoring flag usage, and balancing latency with availability through caching or asynchronous evaluation.

Notable tools and platforms include LaunchDarkly, Unleash, Flagr, and Optimizely, among others. When used well, feature flags support safer, more agile software delivery; when misused, they can create hidden complexity.