Disadvantages and Pitfalls of Web Services
In the previous hour, we looked at what Web services are and how they can be used to solve problems. However, Web services are not a magic bullet solution for every issue; they do have limitations. In this hour, we'll discuss those issues.
In this hour, you will learn
What pitfalls to expect with Web services
What performance issues affect Web services
How a lack of standards affects Web services
How the newness of Web service technology can be a problem
What staffing challenges exist when going with a Web services solution
Pitfalls of Web Services
No technology is perfect. Although Web services do a great job at solving certain problems, they bring along issues of their own. Some of these pitfalls are inherent to the technological foundations upon which Web services are based, and others are based on the specifications themselves. It is important to know what these issues are so that you can plan for and build around them.
Some of the biggest issues are
AvailabilityEveryone who uses the Internet knows that no site is 100% available. It follows that Web services, which use the same infrastructure as Web sites, will not be 100% available either. Even if the server is up and running, your ISP might not be, or the ISP hosting the other side of the transaction might not be either. If you need 100% up time, do something else. Because of this situation, it is often necessary to build mechanisms that will retry the transaction or fail gracefully when this occurs. Some of the newer protocols supported by Web services (JMS, for instance) will handle this automatically, but the majority built on HTTP will not.
Matching RequirementsAny time you create a general service that will handle a variety of customers, you will run into specialized requirements. Some customers might require the one extra little feature that nobody else needs. Web services are envisioned as a "one size fits many customers" technology. If your business can't fit into that model, you should consider other solutions.
Immutable InterfacesIf you invest in creating a Web service for your customers, you have to avoid changing any of the methods that you provide and the parameters that your customers expect. You can create new methods and add them to the service, but if you change existing ones, your customers' programs will break. This is easy to do until you find that one of your existing methods is returning wrong answers and can't be repaired because the approach is fundamentally flawed. Early releases of Java contained methods for calculating date and time differences that could not be made to work correctly. They had no choice but to junk the first set of routines and write new ones. This caused programs to quit working, but there was no choice because the programs were getting wrong answers from the old routines. Although this sort of problem occurs in all systems, it is especially true in Web services. You might not know who is using your service, and as a result you have no way to inform those users of the change. In most other systems, because of the tight coupling, there usually is more verbal or written coordination between producers of a service and consumers of it.
Guaranteed ExecutionThe whole idea behind having a computer program instead of doing a job by hand is that the program can run unattended. HTTP is not a reliable protocol in that it doesn't guarantee delivery or a response. If you need this kind of guarantee, either write the code to retry requests yourself or arrange to send your requests through an intermediary who will perform these retries for you. Again, newer versions of the specification allow for using protocols such as JMS to resolve this issue, but the majority of services out there still utilize HTTP, which does not.
As you can see, with such limitations, Web services might not be right for your needs. This is just the beginning of the list, however.