Cloud Computing actually has a much wider meaning (that sometimes makes it simply look like a marketing trend) so today I will narrow it down and focus on cloud infrastructures. The questions I will try to answer are: what is a cloud infrastructure, and when can you say you're really running your business in the cloud?
To provide the right answers, you have to think of the applications that you want to run on your IT infrastructure. Many of you have probably gone through the server consolidation process that made VMware a billion dollar company: you had lots unused hardware resources but you still wanted to separate operating environments so, no problem, hardware virtualization could solve that for you, without the need to change anything in your application code or architecture. The same application you were running before on the bare-metal would run exactly in the same way inside a virtual machine.
After server consolidation practices became common, somehow the evolution of hardware virtualization went much faster than the evolution of applications. Hypervisor vendors started to provide more and more features to make the underlying hardware always available for running applications, so they could endlessly run without even caring about potential hardware failures.
What people tend to forget when buying powerful hardware platforms is that application failures are much more the primary reason of outages than hardware failures. For this reason, sooner or later you realize that and you have to build up an application-level redundancy in order to implement a real highly available system. But with application-level redundancy, do you still need to have underlying expensive hardware? Why not to run your application on commodity servers?
This question will lead to the real concept of cloud computing. Let's now try to give a definition: a cloud infrastructure can be called so if it:
- is scalable and elastic
- provides process automation (self-provisioning / self-service / billing)
- is highly available
- provides full multi-tenancy
And what is the purpose of all of the above? If you think carefully, you'll realize that it's all aimed at commoditizing the infrastructure itself. Companies shouldn't spend anymore time to build up their IT foundations but they should concentrate on their actual business workflows, supported by really innovative applications. Infrastructure is something they want to take for granted.
In this scenario, a cloud platform should have another important characteristic: it has to be cheap.
So can you achieve all of that with a traditional hardware virtualization-powered infrastructure? No.
Scalability will be an issue if you're using centralized resources (that can't grow big forever) that are usually necessary for providing hardware-level HA.
You will feel safe thanks to all those automatic live machine migration features but don't forget that they protect you only from hardware failures. If the application fails there is not much they can do for you. You should protect yourself from application failures by building a redundant application architecture but, if you do so, do you still need expensive hardware-level HA? No, you don't.
And one more thing, cost. Hardware virtualization infrastructures require complex high-end hardware that won't get the point of being cheap in order to turn the IT infrastructure into a commodity.
In the end, do you want to run your old legacy application in the cloud? Forget it. Just keep it on your powerful expensive virtualization platform. That will work just fine. But if you're a visionary who believes in a future that requires performant, scalable, elastic and cheap commodity IT infrastructures, then choose your next applications to be cloud aware. That will take you much further, much faster.