Feature flags are a software development technique that allows teams to enable, disable or change the behavior of certain features or code paths in a product or service, without modifying the source code.
OpenFeature is an open standard that provides a vendor-agnostic, community-driven API for feature flagging. The flagd project is fully OpenFeature-compliant. In fact, flagd was initially conceived as a reference implementation for an OpenFeature backend, but has become a powerful tool in its own right. For this reason, you'll find flagd's concepts and terminology align with that of the OpenFeature project. Within the context of an OpenFeature-compliant feature flag solution, flagd artifacts and libraries comprise the flag management system and providers. These artifacts and libraries alone won't allow you to evaluate flags in your application - you'll also need the OpenFeature SDK for your language as well, which provides the evaluation API for application developers to use.
Below is a non-exhaustive table of common feature flag use-cases, and how flagd supports them:
| Use case | flagd Feature |
|---|---|
| flag evaluation | Returns the value of a particular feature flag, if the flag is enabled. Supports flags of various types including boolean, numeric, string, and JSON. |
| dynamic configuration | Flag definitions from any sync source are monitored for changes, with some syncs supporting near real time updates. |
| dynamic (context-sensitive) evaluation | flagd evaluations are context sensitive. Rules can use arbitrary context attributes as inputs for flag evaluation logic. |
| fractional evaluation / random assignment | flagd's fractional custom operation supports pseudorandom assignment of flag values. |
| progressive roll-outs | Progressive roll-outs of new features can be accomplished by leveraging the fractional custom operation as well as automation in your build pipeline, SCM, or infrastructure which updates the distribution over time. |