NATS Pub-Sub with storing messages in NATS when there is no subscribers?

[dmitryrn]

I know there is JetStream, but I'm wondering, can you use NATS' Pub-Sub and guarantee to not lose messages when all subscriber services are down and someone is publishing a message? Presumable storing there messages in NATS cluster in RAM.

[ripienaar]

That's the problem JetStream solves, NATS Core is best efforts.

[ripienaar]

Best efforts mean if no-one is listening the message is lost, if the network is interrupted, the message is lost. There is no persistence, retries etc in the core broker.

Clients can use request-reply to know if the message was received and do own retry.

Otherwise stick them in a stream and consume from the stream