Many technologies and ideas are paving the way for cloud computing. Utility computing, grid computing, and virtualization have all played important roles in enabling cloud solutions to take hold. In some ways, SOA is an easy to overlook player in the cloud computing world. However, there's no doubt that without SOA, and the ideas from the SOA movement, cloud computing would not be where it is now.
First, consider the millions of services available in the application services layer of the public cloud. While some of these services are intended to be consumed by an end-user, just as many are meant to be consumed programmatically. Enterprises seek to compose services in the application services layer to deliver larger, end-user applications to their consumers. As such, the ability to consume services that exist across domains and company firewalls is a must. SOA standards help in this respect as they define how services, regardless of location, are discovered, consumed, and governed. This common set of standards has helped to make the services in a public cloud more readily useable by enterprises, so SOA standards have been a key factor in the explosion of service offerings in the public cloud.
Second, and just as important, is the impact that SOA has and will continue to have on the enabling layers of cloud computing. By the enabling layers of the cloud, I mean the platform and infrastructure services layer where we find both application and physical infrastructure. These two layers in the cloud are often referred to as constituting a Service Oriented Infrastructure, so the impact of SOA is immediately obvious. SOA has led to viewing application and physical infrastructure capabilities as discrete services that can be consumed as part of an overall solution or process. As the number of services in these two layers continues to grow, it will be important that they can be discovered, managed, and governed similar to software service components so as to enable robust, composable cloud infrastructure solutions. By applying the principles and lessons of SOA to these enabling services, we can achieve a discoverable, composable, and governable cloud infrastructure.
SOA should be acknowledged as a key enabler to cloud computing solutions. There are of course reasons beyond what is mentioned above. For instance, think about application virtualization and how effective management of such virtualization requires the capability to interact with applications implemented in various technologies. SOA standards have established how to interact and communicate with applications regardless of implementation, so virtualization management can and should piggyback on these standards. As cloud computing continues to evolve, I think we will only see more instances of SOA affecting cloud computing for the better.