I have a publisher and consumer (RPC model), each of them running on different nodes. The publisher publish a message to a specific queue and the consumer listens to the same queue. While consumer processing the message, an exception thrown from the application itself, like invalid argument supplied or any other type of exceptions.
How can I handle this exception and respond the publisher with the exception message ?
If this is an application-level error which the publisher can and should handle, then I think this should be encapsulated at the RPC layer, rather than the transport layer. That is, it should be part of the data you send, not a status of any sort within RabbitMQ.
What I mean by that is that if the response from the consumer currently looks like this:
{"answer": 42, "years": 7500000}
You might change it to indicate success:
{"success": true, "result": {"answer": 42, "years": 7500000}}
Then you can return a message indicating failure instead:
{"success": false, "error": "Unable to reticulate splines"}
It's then up to the code in the publisher to "unwrap" this error and handle it appropriately.
This makes the whole mechanism agnostic of how the RPC works - you could replace RabbitMQ with ZeroMQ, or an HTTP API, etc, and use the same response format to handle the errors.