Middleware & SOA by Example
I am an inexperienced Java developer trying to wrap my head around some fundamental middleware/SOA concepts and technologies, specifically:
- Service-Oriented Architecture (SOA)
- Message-Oriented Middleware (MOM)
- Message Queue
- Apache Camel
- Mule
- EJBs
- Endpoints & Routes
- Service Bus/ESB
- JMS
After looking each of these up online/on Wikipedia, I was able to get (for the most part) decent definitions for each of these. What I am not understanding is how all of these technologies/concepts work together on the backend to provide a 2nd/business tier solution.
Can someone please give an example of an architecture that would use all of these technologies/concepts, and explain what role each of them play in the overall solution? Once I see a working example I'm sure it will help me connect most of the dots.
Edit: Since I added the bounty, I've had several answers that suggest reading books. Although I appreciate all feedback here, I simply can't part ways with 300 reputation points for an answer that, essentially, boils down to "RTM" (especially when I'm flat broke and can't afford the manual!) To reiterate, the bounty and definitive answer will go to someone who can hit all of these bullets in a meaningful, practical example. This does not have to be a middleware compendium!!! Just a paragraph or two that shows how all these can be used together in harmony to produce a Java business-tier solution. Thanks again.
Answer
SOA main principles: Build systems as set of services where each service is
- Coarse-grained
- Interoperable
- Loosely coupled
A company offers a lot of business services (coarse-grained) developed over many years and exposed to the users (human or other systems) in some form. There are more chances that each of these features have been designed and developed not keeping the above three principles in mind. Moreover, each of those features might be running on disparate heterogeneous platforms, using different technologies etc.
What if you want to integrate these disparate features thus creating new solutions (For e.g. Amazon store front is a new service composed of their catalog service, shopping cart service etc)?
You have two choices:
- Building the new feature from scratch keeping the 3 principles in mind. But it is a very costly endeavor, and one that’s almost never successful.
- An effective and less risky alternative is to assemble/compose it from existing, proven (well tested) services.
Option 2 is where ESBs can help with their support for routing, transformation, monitoring etc. Apache Camel, Mule are open-source ESB's. Endpoints & Routes are the terminology used in EIP (Enterprise Integration Patterns) that these ESB's implement. ESB's can take help of MOM's (Message-Oriented-Middleware) when they want to route/integrate services that are running on heterogeneous platforms (For e.g. the catalog service might be running on a mainframe system but the shopping cart is implemented using stateful EJBs running in a Java Application server). Message queue is a concept in MOM that acts a temporary storage of the message between the sender and receiver. This temporary storage provides lot of benefits like asynchronous delivery, guaranteed delivery etc. There are several different MOM vendors like IBM (WebSphere MQ), open-source ActiveMQ etc. We can use JMS to keep your code independent of the vendor.
I tried to relate all the concepts with an example. I also tried to keep it short. Please ask follow up questions to gain more understanding.
MOM is not a requirement to implement SOA. For e.g. if all of your services are exposed over SOAP via HTTP then you don't need a MOM in this case.