NATS 2.12.1

[Kyle Kingsbury]

Esteemed colleagues,

NATS is a popular distributed streaming system. Jepsen tested NATS
2.12.1, focusing on its durable JetStream subsystem, and found that it
could [lose data or get stuck in persistent
split-brain](https://jepsen.io/analyses/nats-2.12.1) in response to
simulated node failures. This data loss was caused in part by a default
`fsync` policy which flushed data to disk once every two minutes, rather
than before acknowledgement. Even a single kernel crash or power
failure, combined with process pauses or network partitions, could cause
NATS replicas to lose acknowledged messages. NATS has documented its
default lazy `fsync` setting, and is considering the other issues we found.

https://jepsen.io/analyses/nats-2.12.1

Please enjoy. :-)

--Kyle