SOA in the Cloud - Monitoring and Management for Reliability
Organizations looking to reduce integration costs are increasingly adopting SOA to maximize to maximize their IT investment
By: Rajiv Totlani
Jul. 20, 2009 06:15 PM
The preeminence of Web services as a tool that can support a wide range of dynamic business processes has made it the SOA tool of choice. Web services are easy to build but difficult and expensive to maintain. Monitoring and management costs weigh heavily on the ROI calculator, and in order to maximize ROI enterprises need to keep a keen eye on the support and reliability meter.
In the Web services world, an application is typically a chain of services, or "links," woven together in some sequence with a Web services front end. The chain itself is weaker than the weakest link in the chain. For example, if an application consists of three service calls, each with a reliability of 0.99, 0.96, 0.97 respectively, the overall application reliability according to the laws of probability and statistics is
Application Reliability = 0.99*0.96*0.97=0.92
The multiplicative effect of individual services tends to steeply reduce overall application reliability as the number of links in the chain increases.
Some of the biggest strengths of Web services, the HTTP and SOAP protocols, are also its weaknesses. HTTP is a stateless protocol that does not guarantee delivery of all the packets to the destination. Nor does it guarantee the order of the arriving packets. This makes HTTP an unreliable protocol incapable of meeting the delivery requirement of "Exactly once". If there is no bandwidth, the packages are discarded. SOAP is the wire protocol for Web services and has some inherent performance problems. Extracting the SOAP body from the SOAP envelope is time-consuming. Parsing megabytes of XML data with a lot of type information is slow and intensive. To increase the reliability of Web services and measure up to the more mature and robust middleware messaging standards, we need to fortify the managing and monitoring of Web services and enhance the reliability of the underlying protocols.
Monitoring and management are the two pillars of reliability. They are related in that the overall goal is to ensure that the QoS objectives are met. Monitoring is a "fault detection" mechanism that checks the health of a service in real time and tries to reduce application downtimes by detecting signs of failure. It ensures that the service is available, accessible, and capable of meeting the throughput and latency requirements. Management is a "fault avoidance" mechanism that lays down rules and policies that makes the service more reliable, usable, and robust. Management ensures that the services can be deployed in a consistent manner, configured from an easy-to-use user interface and meet the overall security and auditing requirements. Within an IT department, usually different groups are responsible for these two functions, so a degree of separation between them is desirable.
Monitoring: The Pulse of Web Services
A Web service must be "coded" for monitoring during development if the Web service development toolkit does not support these monitoring options. Nearly all the big Web service providers - like IBM, TIBCO, BEA, and Microsoft - either have built-in support for availability and performance or are planning it in the next release.
Management: The Nerve of Web Services
Web services need to be "instrumented" for management if the service provider does not support some of the vital management functions. The management objective is the one in which the Web service providers need to catch up. Most support deployment from a centralized console. Some of them support versioning directly; most support it indirectly through namespaces. None of them support the entire spectrum of security requirements and most of them do not support management policies. This has led to the growth of a unique class of middleware in the Web services world called Web Services Intermediaries (WSI). These intermediaries (like Oblix, Actional, AmberPoint and Ensemble) specialize in monitoring and management activities.
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