Message Queues: Are messages lost on network failure?

Question

I am wondering about the reliabilty of message delivery in messaging systems such as WebsphereMQ or ActiveMQ (used via JMS). As far as I know messages can be buffered if the recepient is unavailable and will be delivered later.

Now I am wondering what happens if the sender temporarily cannot reach the network. Is there some kind of local buffering which will send the messages later? I assume this depends on where the message broker is running. Are there local brokers on all machines or just a central one?

To pinpoint my question: Is a messaging system the right choice if I need to ensure, that messages are received eventually, even in the face of temporary network failure? Is there a certain setup required to achieve this reliabilty?

Any pointers to relevant documentation would be appreciated.

Answer 1

The common solution is called "store and forward". In such systems, once you've handed off the message to the local message agent it becomes their responsibility. This agent might not be a full broker. If the messaging system has basic delivery guarantees, the local agent will still need persistent buffering of messages until they're handed off to a real broker.

Answer 2

If you really can't afford to lose messages I'd recommend implementing a reliable messaging pattern at the endpoints if you can, i.e. the sender re-sends if no acknowledgement is received within a certain time period and the receiver has duplicate detection to cope with receiving the same message more than once.

Guaranteed delivery comes with a performance overhead and usually doesn't give any guarantee as to how long your message might take to get there.