Message broker vs. MOM (Message-Oriented Middleware)

Question

I'm a little confused as to what the difference is between a message broker e.g. RabbitMQ and Message-orientated Middleware. I can't find much info apart from what's on Wikipedia. When searching MOM I find info on AMQP which states is a protocol for MOM.. what does this mean? What is MOM then? I also have read that RabbitMQ implements the AMPQ protocol.. so why does that make a RabbitMQ a messsage broker? Are a message broker and MOM the same thing?

Hope some can unravel my confusion. thanks

Answer 1

An overview -

• A protocol - A set of rules.
• AMQP - AMQP is an open internet protocol for reliably sending and receiving messages.
• MOM (message-oriented-middleware) - is an approach, an architecture for distributed system i.e. a middle layer for the whole distributed system, where there's lot of internal communication (a component is querying data, and then needs to send it to the other component, which will be doing some processing on the data) so components have to share info/data among them.
• Message broker - is any system (in MOM) which handles messages (sending as well as receiving), or to be more precise which routes messages to the specific consumer/recipient. A Message Broker is typically built upon a MOM. The MOM provides the base communication among the applications, and things like message persistence and guaranteed delivery. "Message brokers are a building block of Message oriented middleware."
• Rabbitmq - a message broker; a MOM implementation; an open-source implementation of AMQP; as per Wikipedia:

  RabbitMQ is an open source message broker software (sometimes called message-oriented middleware) that implements the Advanced Message Queuing Protocol (AMQP).

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As you asked:

When searching MOM I find info on AMQP which states is a protocol for MOM.. what does this mean?

MOM is about having a messaging middleware (middle layer) between (distributed) system components, and AMQP is protocol (set of rules) for reliably sending and receiving messages. So, a MOM implementation (i.e. Rabbitmq) may use AMQP.

What is MOM then?

Message-Oriented-Middleware - is an approach, an architecture for distributed system i.e. a middle layer for the whole distributed system, where there's lot of internal communication (a component is querying data, and then needs to send it to the other component, which will be doing some processing on the data) so components have to share info/data among them. In short it's a way to design a system, for example: depending upon the overall requirements we need to develop a distributed system, with some internal communication. The biggest advantage of MOM architecture/decision is decoupling of the components i.e. if we're going to change the data query component it'll have no effect on the data processing components, as they're communicating via MOM (e.g. Rabbitmq Cluster) - the data processing component is getting the data in form messages, which then parses and processes them.

MOM at the end is just a design decision, that we use a middleware for gluing our system (distributed) components, a middleware for handling communication between them, in the form of messages (i.e. JSON). To implement a message-oriented-middleware we need more - set of specific rules i.e. how the messages will be published, consumed, how the acknowledgement will work, the lifetime of a message is until it is consumed, the persistence of a message, etc. AMQP is basically these set of rules i.e. a standard/protocol for implementing a MOM i.e. a messaging system using AMQP, means it confines itself by the stated rules. From Wikipedia:

AMQP mandates the behavior of the messaging provider and client to the extent that implementations from different vendors are inter-operable, in the same way as SMTP, HTTP, FTP, etc. have created inter-operable systems.

I also have read that RabbitMQ implements the AMPQ protocol.. so why does that make a RabbitMQ a message broker?

Yes, Rabbitmq is a message broker (publisher -> exchange -> queue -> consumer). It's an open source AMQP implementation i.e. a messaging system/broker which confines to AMQP (the AMQP rules) - one can use Rabbitmq as the middleware, hence MOM.

AMQP - is just a set of rules i.e .how messages will be published, kept (in queues), consumed, delivery acknowledgement, etc.

Are a message broker and MOM the same thing?

In simple words, Yes. If we need to go with MOM design for our distributed system, we can simply use Rabbitmq (a message broker; an AMQP implementation) as the middleware.