SOA in Practice

Chapter 4. Loose Coupling

SOA APPLIES TO LARGE DISTRIBUTED SYSTEMS. SCALABILITY AND FAULT TOLERANCE ARE KEY TO THE maintainability of such systems. Another important goal is to minimize the impact of modifications and failures on the system landscape as a whole. Thus, loose coupling is a key concept of SOA.

This chapter will discuss the motivations for this concept (for large distributed systems), exploring variations of loose coupling from the technical and organizational points of view. This topic will demonstrate that SOA is a paradigm that leads to special priorities when designing large systems. However, again, there is no rule prescribing which kind or level of loose coupling you should employ. This decision must be made based on your specific circumstances.

The Need for Fault Tolerance

We live in crazy times. The market rules, which means you won’t usually have enough time to create well-elaborated, robust system designs. If you’re not fast enough, flexible enough, and cheap enough, you’ll soon find yourself out of the market. Thus, you need fast, flexible, and cheap solutions.

Fast and cheap solutions, however, can’t be well designed and robust. Consequently, you will have to deal with errors and problems. The important point here is fault tolerance. The most important thing is that your systems run. According to [ITSecCity02], a flightbooking system failure may cost $100,000 an hour, a credit card system breakdown may cost $300,000 an hour, and a stock-trading malfunction ...