SOA and SLA

As architects and developers pull together more and more services into larger services and business processes a much closer examination of the quality of those services and the service level agreements (SLA) must be made and documented. The throughput and uptime, the types of bindings and transports, the capability of participatingin a transaction or providing a certain level of security are all examples of service level agreements that extend beyond just the schema contract.

Consider a larger business process that is made up of a half a dozen services. If any one of the services as part of the business process fails to meet certain criteria then the entire business process might fall below it's SLA. A service that claims a certain SLA today must continue to provide the same level of service tomorrow in order not to effect the service level of the composite services and business processes it is a part of.

This is where all the governance that people are talking about comes in. For early SOA adoption this type of governance might not make sense but as the extent of your SOA grows and services start to be reused more and more then governance is required and great care must be taken to examine each services SLA and provide enough information so that other services can consume it with confidence.

So is all this some tedious effort to just come up with more documentation? More standards? More XML? On the contrary SLA and governance becomes a powerful ally in analyzing, developing and testing new services. So much of the cost of making changes to your business are about the effects on existing assets. Understand the SLAs across the various services provided by IT helps testing services as part of composites and business processes and, more powerfully, help reduce the cost of regression testing in future development life cycles. After all that is where much of the business agility promised by SOA comes in - the ability to adapt your IT to changing business needs at greater speed and efficiency.

There are a number of initiatives that are trying to address governance and SLA. Notably the W3C's WS-Policy.