The rule of the "cloud" has already been established and now we have multiple vendors fighting for market share. Many companies started relying on the cloud and seeking more and more automation and could services. It looks easy, you just select a cloud provider, use it's services and you have several virtual machines or containers within minutes. Sounds like magic? Well, Here is the question you are probably asking yourself . What is behind it all? The answer is; good old virtualization, strong APIs and scripting. I guess most of you, who are to some extent already familiar with vitualization, and have the affinity to work with opensource technologies have used Xen. It was the very first in the opensource world, and that is for sure. Its first release was in 2002 and it definitely became one of the dominant virtualization solutions in the opensource world. If we take a look at the main vendors like Oracle for example, we will see that behind OVM is again Xen. At the same time lots of companies started using another solution, which you might have heard of - Citrix. The company that created it became very well known.