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Request Reply
NATS supports two flavors of request reply messaging: point-to-point or one-to-many. Point-to-point involves the fastest or first to respond. In a one-to-many exchange, you can set a limit on the number of responses the requestor may receive or use a timeout to limit on the speed of the response.
In a request-response exchange the publish request operation publishes a message with a reply subject expecting a response on that reply subject. Many libraries allow you to use a function that will automatically wait for a response with a timeout. You can also handle that waiting process yourself.
The common pattern used by the libraries is that the request creates a unique inbox and performs a request call with the inbox reply and returns the first reply received. This is optimized in the case of multiple responses by ignoring later responses automatically.
digraph nats_request_reply {
rankdir=LR
subgraph {
publisher [shape=box, style="rounded", label="Publisher"];
}
subgraph {
subject [shape=circle, label="Subject"];
reply [shape=circle, label="Reply"];
{rank = same subject reply}
}
subgraph {
sub1 [shape=box, style="rounded", label="Subscriber"];
sub2 [shape=box, style="rounded", label="Subscriber"];
sub3 [shape=box, style="rounded", label="Subscriber"];
}
publisher -> subject [label="msg1"];
publisher -> reply [style="invis", weight=2];
reply -> sub3 [style="invis", weight=2];
subject -> sub1 [label="msg1", style="dotted"];
subject -> sub2 [label="msg1", style="dotted"];
subject -> sub3 [label="msg1"];
sub3 -> reply;
reply -> publisher;
}
Try NATS request reply on your own, using a live server by walking through the request/reply tutorial.