Jepsen: NATS 2.12.1
1 Background NATS is a popular streaming system. Producers publish messages to streams, and consumers subscribe to those streams, fetching messages from them. Regular NATS streams are allowed to drop messages. However, NATS has a subsystem called JetStream, which uses the Raft consensus algorithm to replicate data among nodes. JetStream promises “at least once” delivery: messages may be duplicated, but acknowledged messages1 should not be lost.2 Moreover, JetStream streams are totally ordered logs. JetStream is intended to “self-heal and always be available”. The documentation also states that “the formal consistency model of NATS JetStream is Linearizable”. At most one of these claims can be true: the CAP theorem tells us that Linearizable systems can not be totally…
