Patterns: Implementing Self-Service in an SOA Environment

Chapter 3. SOA and the Enterprise Service Bus 45

Service interaction

The ESB needs to support SOA concepts for the use of interfaces and support

declaration service operations and quality of service requirements. The ESB

should also support service messaging models consistent with those interfaces,

and be capable of transmitting the required interaction context, such as security,

transaction or message correlation information.

Management

As with any other infrastructure component, the ESB needs to have

administration capabilities so that it can be managed and monitored to provide a

point of control over service addressing and naming. In addition, it should be

capable of integration into systems management software.

3.2.5 ESB and Web services technologies

Given the prominence of Web services technologies in current discussions of

SOA and the fact that many successful implementations of Web services

technologies exist, it is interesting to analyze what the use of basic Web services

technologies (WSDL and SOAP/HTTP) achieves against the minimum ESB

capabilities that are described in 3.2.4, “Minimum ESB capabilities” on page 43.

Using basic Web services technologies achieves:

򐂰 URL addressing and the existing HTTP and DNS infrastructure provide a bus

with routing services and location transparency.

򐂰 SOAP/HTTP supports the request/response messaging paradigm.

򐂰 The HTTP transport protocol is widely available.

򐂰 SOAP and WSDL are an open, implementation-independent messaging and

interfacing model.

Although the use of SOAP/HTTP and WSDL in this way has many advantages,

this scenario falls short of the minimum capabilities of the ESB in the following

ways:

򐂰 The scenario relies on the provision of interoperable SOAP/HTTP enablement

of each participating system. Because the Web services standards are

continuing to mature, there are many systems for which this will not be

feasible. An ESB should provide some form of support for alternative

integration techniques.

򐂰 Control over service addressing and routing is dispersed between client

invocation code, adapter configurations, and the DNS infrastructure. There is

no single point of infrastructure control. In other words, this is a point-to-point

integration style.