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Hypervisor indecisive? Today's contenders from yesterday's Hipsters

Virtualisation from bearded types who liked it before it was cool

Open-source alternatives

Another open-source virtualisation platform is KVM – that’s Kernel-based Virtual Machine, not Keyboard, Video and Mouse – a hosted hypervisor that sits upon other Linux or BSD distributions. From Debian to Red Hat, and Gentoo to Ubuntu, KVM is the hypervisor of choice for those Penguin-fanciers who prefer to virtualise atop a system they are familiar with.

It’s a similar argument to those core Windows sysadmins who favour Hyper-V for their data centres. They would far rather accept the limitations of a platform they know intimately, can troubleshoot easily and tinker under the hood of, than work with a system that might have a better reputation for reliability or perhaps more functionality, but is ultimately a closed black box – a difference engine whose inner workings they simply do not understand.

Like Xen, KVM finds itself very popular among the virtualisation community at large as a result of its propensity for interfacing well with others. Quick Emulator (or QEMU for short) is a perfectly good piece of software in its own right and is chiefly used for virtualising user-level applications and processes.

But when combined with another hypervisor, such as Xen or KVM, its functionality is increased and improved.

Libvirt, on the other hand, is a library of virtual APIs that extend and improve the management of other virtualisation systems. It is on this basis, of extending the functionality and management abilities of a series of hypervisors, that the modern cloud stack as we know it came to pass. OpenCloud and CloudStack form the basis of most enormous cloud platforms.

The real benefit of these cloud platforms based upon Xen and KVM – when they are well written and implemented with an easy-to-use, self-service interface at any rate – is that they democratise the use and spread of virtualisation platforms, allowing those other than hardened sysadmins and virtualisation specialists to reap the benefits of the technology.

The new (old) way – containers and docks

The next big alternative to the classic hypervisor comes in the form of the container.

If FreeBSD is your operating system of choice, then the comically named BSD Jail mechanism will be familiar to you as a method of virtualisation. Rather than creating a discrete virtual machine, including paravirtualising hardware, device drivers and a guest operating system, the BSD admin can subdivide the core operating system resources into compartmentalised workloads known as "jails", allowing for fine-grain segregation of physical resource, data and security among these sub-machines.

If you prefer penguins (Linux) to small red devils (the Unix-like BSD) then you might want to try OpenVirtuozzo – or OpenVZ to its friends – as your package of choice for compartmentalising workloads on CentOS, Debian, Fedora, Suse or Ubuntu.

This method of operating system-level virtualisation – known as containers – is becoming increasingly popular, and the cool new kid on the block is called Docker.

While most virtualisation technologies aim at the machine-level, Docker is designed as an application container, and offers the same levels of abstraction and segregation of resources, workloads and security to the application environment.

It is still a Linux-based operating system-level virtualisation technology (similar to OpenVZ) but the management interface and operating parameters have been adjusted to make it fit better with software as the target.

Docker lets you segregate software implementations by customer without needing to go to the additional effort of virtualising guest operating systems. This suits development shops perfectly, granting the ability to differentiate different forks and branches or live builds and test environments with the minimum of fuss and bluster, in much the same way that well-implemented public clouds allow easy access into operating-system virtualisation.

Docker might well be seen as picking low-hanging fruit or selective virtualisation, but it’s a solution that works: why spend time, energy and money virtualising more than you have to?

IBM Unix/AIX sysadmins are already fairly Hipster-like thanks to a certain taste for bushy beards and plaid shirts, but they will take any opportunity to remind you that they were virtualising “before it was cool” with the original virtual containers – LPARs – on IBM pSeries/zSeries hardware.

With the rise of the container as a method of virtualisation I’m reminded of Big Blue’s LPAR system and how logical partitions kick-started the technologies we have come to rely on, and can’t help but think we are coming full circle. ®

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