Question

I am not a senior programmer but I have been deploying applications for a while and devloped small complete systems.

I am starting to hear about queueing systems such as RabbitMQ. May be, I never developed any systems that had to use a queueing system. But, I am worried if I am not using it because I have no idea what to do with this. I have read RabbitMQ tutorial on their site but I am not sure why I would use this for. I am not sure if any of those cannot be achieved by conventional programming with no additional component and regular databases or similar.

Can someone please explain why I would use a queueing system with a small example. I mean not a hello world example, but a a practical scenario.

Thanks a lot for your time

• RM

Answer 1

One of the key uses of middleware like message queues is to be able to send data between non homogenous systems. The messages themselves can be many things. Strings are the easiest to be understood by different languages on different systems but are often less useful for transferring more meaningful data. As a result JSON and XML are very popular for the messages. These are just structured strings that can be converted into objects in the language of choice at the consumer end.

Additional useful features:

• In some MQ systems like RabbitMQ (not true in all MQ systems) is that the client handles the communication side of things very nicely.
• The messages can be asynchronous. If the consumer goes down, the messages will remain until the consumer is back online.
• The MQ system can be setup to varying degrees of message durability. They can be removed from the queue once read or remain until the are acknowledged. They can be persistent so even if the MQ systems goes down message will not be lost.

Here goes with some possibly contrived examples. A Java program on a local system wants to send a message to a system on the connected through the internet. The local system has a server connected to the internet. Everything is blocked coming from the internet except a connection to the MQ. The Java program can publish the message to the MQ with out needing access to the internet. The message sits on the queue until the external system picks it up. The Java program publishes a message, lets say XML, and the consumer could be a Perl program. As long as they have some way of understanding the XML with a predefined way of serialization and deserialization it will be fine.