orleans

# Microsoft Orleans ## Start With Purpose Do not begin with an Orleans API. First state: 1. the business identity that owns the behavior; 2. the invariant and what must survive activation or cluster failure; 3. the required consistency, query shape, acknowledgement, durability, replay, fan-out, and timing. Then select the smallest Orleans primitive whose guarantees match those requirements. Reject Orleans when the problem is primarily shared-memory computation, a finite batch, relational querying, or global coordination with few independent entities. Inspect package versions for version-sensitive work. Orleans `10.2.1` ships `Microsoft.Orleans.DurableJobs*` and `Microsoft.Orleans.Journaling*` as `10.2.1-alpha.1`; treat them as experimental until that status changes. ## Mental Model - A **grain** is a virtual actor: a logical entity with stable identity, behavior, and optional state. It is not a process, row, DTO, controller, or background job. - A **grain reference** is a location-transparent address. Getting a reference does not create a durable record or prove that an activation exists. - An **activation** is an ephemeral in-memory execution instance. Orleans creates, places, moves, deactivates, and recreates it. Never equate activation lifetime with entity lifetime. - A normal grain has at most one activation in the cluster by default and processes turns one at a time. This makes the grain a natural owner of per-identity invariants. - A **silo** hosts activations. S...