Many organisations claim that they have migrated to the cloud. When you ask them how? The answer is we have forklifted the VMs as-is into a private/public cloud platform. Congratulations! You are on the cloud but are you really leveraging the cloud computing capabilities?
Probably the on-demand provisioning capability in case of public cloud which could be useful for dev/test servers but how often will you switch a production server off in order to save computing costs? Hence, the cloud platform is merely used here as a virtualisation platform in case of a private cloud or a virtual colocation/server hosting facility to potentially reduce TCO by saving data centre costs in case of a public cloud. Actually, from IT operations management perspective the cloud platform could be counter-productive in this scenario since it doesn't provide helpful VM management features to manage virtual machines that standard virtualisation platforms provide like 'live migration' and comprehensive snapshotting.
A true cloud platform offers an abstraction/virtualisation layer, a set of building blocks, and an API. Cloud computing is all about leveraging this API to combine the provided building blocks and build a custom solution that can be elastic, scalable, and highly available if it has been designed correctly. A critical success factor for such a design is loose-coupling where the main components of a system is independent from each other and communicate with each other through well defined interfaces and protocols. Therefore, they can be autoscaled horizontally based on demands and independent from each other.
SOA systems are inherently ready to be migrated as-is to the cloud and leverage the cloud computing capabilities but many systems need to be deconstructed into loosely-coupled components in order to be migrated to the cloud and reap the cloud computing benefits of elasticity, scalability, high-availaiblity, and agility. The bottom line is if a server runs on the cloud it doesn't mean it's leveraging the cloud computing capabilities.