OK, this may be a pun, but it's true. Getting your arms around this virtual stuff is hard.
That's particularly true when the drivers for virtualization are quite diverse. One common element in all of the virtualization concepts is the notion of an abstraction, something that lets users work with something easy and disguises the hard stuff. From there, you're on your own. The good news is that you can go pretty far with this simple start, particularly if you apply the abstraction notion first to the data center.
Along came the VMs
Virtualization got introduced to IT and the data center when "virtual machines," or VMs, came along. Even this single trend had multiple drivers. Hardware was growing in power, with CPUs adding cores and servers adding CPUs. The result was a steady growth in compute power, more and more of which was wasted by traditional multi-programming operating systems.
Part of the reason for the waste was that many applications needed to be isolated from other apps, either to secure stable performance or to resolve security/governance concerns. VMs are an abstraction of hardware, representing something that looks like a server and can be managed like a server, but that resides with other VMs on the same physical device. Isolated, protected, abstracted.
Containers, which are simple lightweight virtual elements that also share a server, have been exploding in popularity because they use fewer server resources than VMs and thus allow more applications to be packed into a given data center. Every data center, even those for mid-sized businesses, likely will become totally virtualized using one or both of these technologies.
Virtual networks, in two flavors
And that's created the second dimension of data center abstraction. Sharing a network is like sharing a server in many ways. You have the risk that application traffic crosstalk will create performance issues. You have the risk of security breaches and the failure of compliance audits. Almost from the first of the VM deployments, people recognized that you needed virtual networks to connect the VMs or containers.
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