Virtualisation Containerisation System |
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While we're here, let's talk about "the cloud". The cynical take is that "the
cloud" just means "your code is running on someone else's computers", but
there's also a strong implication that the computer running the code you're
using is actually a virtual machine, created and destroyed as demand rises and
falls. Companies like Amazon and Rackspace will rent you a virtual machine - or
a thousand virtual machines! - by the hour, running them on physical hardware
somewhere in their datacentres. They take a cut, of course, but the ability to
add more servers simply by clicking a button or writing a line of code may well
be worth the extra money: this is how Instagram grew so huge with such a small
team. |
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It's also possible for a virtualisation layer to run on top
of an operating system; we refer to the OS that's running
directly on the hardware as the host operating system, and
the ones that are running virtually as guests. This allows
you, for instance, to run a Windows VM on your Mac or Linux
development machine, so you can see how your site will look
in Internet Explorer (or, as it's known among techies,
Internet &#%Ģing Explorer).
Examples of virtualisation systems at this level:
KVM, Virtualbox, QEMU.
Containerisation (also known as "OS-level virtualisation")
is similar to virtualisation, but less flexible (you can
only run a Linux container on a Linux host), and less
resource-intensive - a machine that can only host a few
VMs may well be able to host hundreds of containers. They
are currently extremely hip, but they require a change of
mindset and the industry as a whole hasn't quite got its
collective mind around them.
Examples: Docker, LXC, BSD jails.
Things we then need to look at:
Lower level:
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Root node:
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Higher level:
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