SDK paradigms

OpenFeature SDKs come in two "flavors"; those intended for use in server applications and those intended for use in client applications. The primary difference between these two paradigms has to do with the way they model evaluation context.

Dynamic Context Paradigm (Server-side SDKs)

In server usage, the evaluation context changes frequently, as often as every evaluation. Though some context data may remain static for the entire application lifecycle (such as the hostname or application version) much of it may be dynamic. For instance, on a web-server, the context might contain the remote IP of the connected client or the session-id or email address of the logged-in user. For this reason, the evaluation API defines a parameter for the evaluation context which can be provided at each evaluation.

Static Context Paradigms (Client-side SDKs)

In client-side usage, the evaluation context changes less frequently, often in response to user actions or UI events. In this case, the context frequently corresponds to a single user, and the context data represents facts about them (such as their name or subscription level) or the application state (if the user has items in their cart). When the context data changes, it's often necessary for the provider to update it's cache of evaluated flags, or request an updated ruleset from the server; we refer to this as context reconciliation. SDKs using the static-context paradigm define a context changed handler for providers to implement which runs any time the context is modified. Client-side implementations include some additional event types: PROVIDER_RECONCILING and PROVIDER_CONTEXT_CHANGED. These are emitted when the provider's context is invalidated, and after it's subsequently reconciled, accordingly.