Shoring up Web services

When your Web Services move beyond the research stage and you start considering deployment, a production-quality SOAP server becomes a necessity. Just as a Web server provides a platform for deploying Web sites and applications, SOAP servers provide the necessary infrastructure for creating reliable and scalable Web services.

Systinet Server for Java 5.0 (formerly Systinet WASP [Web Applications and Services Platform] Server) is a production-quality SOAP server with management features that will make your operations group smile. This release of Systinet Server also provides support for reliable message exchange using the WS-Addressing, WS-Policy, and WS-RM (WS-ReliableMessaging) standards.

The reliable delivery of messages is crucial if Web services are to become part of the mission-critical infrastructure that integrates applications inside and outside of the enterprise. Many business problems require that participants be assured that message exchanges will be completed. Without support for reliable messaging, the application developer becomes responsible for ensuring that messages are delivered and for avoiding duplicate message processing. This is impractical. Ad hoc, application-level solutions make it difficult and costly to extend services to other partners.

WS-Addressing gives Systinet Server a way to specify end points for SOAP services. WS-Addressing creates end point references that augment URI (Uniform Resource Identifier) information with application-specific information useful for dispatching the message. WS-Addressing’s concrete end point specifications allow Systinet Server to correlate requests with responses. This is not only necessary for reliable messaging but also a great boon to server scalability. Because a final destination can be negotiated, it allows multiple servers to go into service behind a load balancer without sacrificing reliable messaging.

I installed Systinet Server for Java on Red Hat Linux 9.0 running Java 1.4.2. Systinet’s wizard makes installation painless. Because the server is configured out of the box, it runs in stand-alone mode and is suitable for testing and small pilot projects. There are numerous configuration options for deploying a production-level server, and they are covered in detail in the 729-page manual. I ran clients against the Systinet Server from a PowerBook running Mac OS X 10.3, using the included SOAPSpy tool to view the SOAP messages traveling between client and server.

Systinet provides dozens of demos that show how to use various features of the product from both the server and client perspectives. I used these to test the server and concentrated on the WS-RM features because Systinet Server is the first product to support the standard. The support for WS-RM depends on the client, the service, or both implementing and using WS-RM’s Sequence API. Sequences are the key to reliable messaging because they are used to uniquely identity messages, find duplicates, and create a reliability context for message acknowledgement.

Systinet Server supports the reliable exchange of messages in a synchronous or asynchronous fashion, and as one-way invocations or as request-response pairs. When request-response messaging is done reliably, two reliable channels are set up to handle both directions. During my tests, using both one-way invocations and request-response, I discovered it was possible to start the client with the service offline; messages were finally delivered when the service came back up.