Every week we find something new for you to explore and give a try. This time the real pearl happen to be found for Elixir users. Meet FunWithFlags, the Elixir feature flag library!
Let’s start from the beginning. Feature flags, or feature toggles, are boolean values associated to a name. They should be used to control whether some application feature is enabled or disabled, and they are meant to be modified at runtime while an application is running. This is usually done by the people who control the application.
FunWithFlags is an OTP application that provides a 2-level storage to save and retrieve feature flags, an Elixir API to toggle and query them, and a web dashboard as control panel.
It stores flag information in Redis or a RDBMS (with Ecto) for persistence and synchronization across different nodes, but it also maintains a local cache in an ETS table for fast lookups. When flags are added or toggled on a node, the other nodes are notified via PubSub and reload their local ETS caches.