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Established container solutions in Linux

Old Hands

Article from ADMIN 31/2016

By Martin Loschwitz

Container solutions are not newcomers to the virtualization scene; they have existed for years. We look at the different flavors available for Linux systems.

When talk turns to Linux and container virtualization, the name you nearly always hear is Docker. Docker has managed to plant its name with a certain amount of force in the administrator's field of view and IT strategies. In fact, you might gain the impression that Docker invented container virtualization for Linux systems. However, it has been around for about 15 years and has been in production use for a long time. In this article, I reveal why containers are so attractive to administrators and the fundamental approaches that vie for the administrator's attention.

Containers vs. Full Virtualization

Virtualization comes in different flavors. In one camp are full virtualizers, in the form of virtual computers, that give you a complete system with a virtual BIOS that looks like a physical server to the software running on it. Under normal circumstances, the software on the VM doesn't even notice that it is not running on metal. Today, administrators typically choose this approach. Paravirtualization in particular has helped popularize full virtualization. In paravirtualization, the virtualizer makes better use of the host's hardware, thus resulting in better performance.

Full virtualization has one major disadvantage, however: Because this approach always simulates a complete computer, it also generates more overhead. To put it another way, by running multiple virtual machines (e.g., with KVM and Qemu or Xen) the host wastes resources that would otherwise be available to the virtualized computers.

On a small scale, this effect is not particularly tragic, but the problem scales with the environment. Cloud service providers in particular are affected: The more virtual machines they have running in a setup (and need to manage), the greater the overhead. Therefore, the density of virtual machines per host or rack is limited, which affects the planning of large-scale data centers and

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