Container-Based OS Virtualization

The Big Trade-Off

There are undeniably a few downsides to this way of approaching virtualization. The first that comes to mind is that when density on a single hardware platform increases, so does its needs for constant availability. Using a single kernel in this case raises the concern on whether the kernel becomes an important single point of failure in the system. Unlike hypervisors, which are in a sense very light-weight and therefore very stable kernels, container-based OS virtualization depends on a slightly modified version of already existing kernels, thus essentially taking over existing weaknesses of both the Windows and Linux platforms.

It has to be noted that a lot of work is put into ensuring kernel stability on all container-based solutions, and unexpected kernel crashes are at least deemed "unlikely". Nevertheless, a bit of healthy paranoia when IT is involved is certainly not an obsolete luxury.

Secondly, while a strong feature set is definitely maintained, containers do take away a lot of flexibility from the hypervisor-based solutions. For one, many might find the inability to use different OSes next to each other a big handicap. Moreover, while support for live migration does exist on Linux systems (both OpenVZ and Virtuozzo have implemented this), it is still missing on Windows implementations. In addition, changing critical system-wide settings is not allowed from within a container - e.g., users are not able to partition their own disk and change file systems at their leisure.

Sadly enough, despite all its possibilities, container-based OS virtualization is most limited, it seems, by its plain invisibility in the current market place. For some reason, it has been quietly pushed into the background by all the current hype surrounding different virtualization technologies, with major software companies fighting for domination of this "gold mine". While it is currently used by most if not all hosting companies, this type of virtualization seems unable to expand its customer base beyond that. Whether through lack of marketing power or a seemingly less attractive feature list, most businesses seem unaware of its potential. Naturally, it goes without saying that just like hypervisors aren't the perfect "one size fits all" solution, neither are containers, but it is still rather peculiar how a solution this prevalent in the IT world could escape the recent surge of interest into virtualization and all its aspects.

Now, it's time to dive straight into the inner workings of what make containers happen.