Glossary

Canonical API -- The QuorumKit public headers under include/quorumkit/. New code should target this surface.

Compatibility surface -- The braft public headers under include/braft/. They preserve source compatibility for existing integrations and forward into the QuorumKit implementation.

Deterministic core -- The Raft state machine at the center of the library. It processes inputs in a fixed order and does not call the clock, the network, or the disk directly. This makes it possible to test under simulated time and simulated faults.

Runtime adapter -- Code that supplies the services the core cannot provide for itself: real clocks, thread scheduling, random number generation, and so on.

Transport adapter -- Code that moves Raft protocol messages between nodes. The core produces and consumes messages; the transport adapter decides whether they travel over brpc, raw TCP, RDMA, or an in-memory channel (for tests).

Storage backend family -- A coordinated implementation of log storage, metadata storage, and snapshot storage chosen together as one backend option.

Dual write -- A migration mode in which QuorumKit applies the same logical durable mutations to two backend families so either one can be used for cutover or rollback.

Bootstrap -- Initializing an empty destination backend family from the durable state exported by a source backend family.

Canonical bootstrap image -- A backend-neutral representation of durable Raft state used to bootstrap one backend family from another without requiring pairwise migration adapters.

Wire compatibility -- The requirement that QuorumKit continue speaking the legacy braft network protocol during mixed-version rollouts.

Rolling migration -- Replacing nodes in a live cluster without a flag day for application code, wire protocol, or durable state.

Export cut -- A logical point between durable mutations used to define one coherent storage snapshot for bootstrap and validation.

Validation cut -- A named logical point in the durable mutation history used when comparing source and destination state.

Logical equivalence -- Equality of Raft-visible durable state, without requiring identical on-disk bytes or layout.