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The Trouble with Clouds Is the Darn Hypervisor

Parallels’ CTO of server virtualization James Bottomley claims there’s an inherent tenancy problem with PaaS and SaaS clouds

Parallels' CTO of server virtualization James Bottomley claims there's an inherent tenancy problem with PaaS and SaaS clouds because most applications are designed for single occupancy.

And they're designed for single occupancy mostly because it's easier to write them that way, ignoring the fact that their data can leak or they can hog resources - or maybe not get enough resources - if they're deployed in a multitenant cloud.

He figures the software industry will pretty much treat the problem the way it did the need for high availability some years back and stick its head in the sand. Single-occupancy applications won't get rewritten to oblige multitenant clouds. ISVs are unwilling to make the investment.

The other problem clouds have, he says, taking a clear shot at rival VMware, is hypervisors. Hypervisors limit density, which is supposed to be a cloud trademark. But hypervisor-based virtualization, and the hype surrounding it, blinkered everyone to other technologies. If it's not a hypervisor, the enterprise isn't interested even though it should be.

Which brings us to what Bottomley says is the solution to the security issues of multitenancy and the density issues of hypervisors. In both cases it's the same solution: containers.

Google saw the advantages of containers and hired Paul Menage, the main Cgroup containers guy, then set about containerizing its main data centers. Google Search, Gmail and Google web services are entirely containerized. When you fire up a search or log into Gmail, you get your very own container running in the Google data centers.

Ditto Facebook.

Naturally, there's another standard, used by a lot of hosters, called OpenVZ, which evolved separately though pieces of both are out of the mainstream.

See, containers share the same kernel - even the same base operating system - and isolate applications from each other and may even provide them different isolated storage.

Hypervisors, on the other hand, run separate copies of the kernel, which is where things start getting messy.

Aside from being more secure, containers can support three times the Virtual Private Server (VPS) density of hypervisors.

Bottomley says the reason containers are denser is partly the simple mathematics of resource savings. Containers run only one kernel per physical system while hypervisors run one kernel per virtual machine (plus one for the host). But it's also due to better management.

The single host kernel in the containers' case has complete visibility into the resource use in the entire system (including what every container is doing). Hypervisors, he says, have to invent all sorts of communication paradigms for the multiple kernels to tell the host what they're doing (ballooning, KSM, performance counters).

Elasticity is the other trademark of the cloud. Containers are also supposed to be more elastic than hypervisors. Since the kernel is already booted, even if you have different operating systems sharing the same kernel and going through a boot sequence, it's still faster than booting a kernel from scratch. If your operating systems are homogeneous, say, the same version of Linux, then booting is instant and you can just start your applications.

That brings us to Linux, the cloud's favorite operating system.

Parallels has been working with Linus Torvalds so the Linux kernel will be sufficiently container-aware and Bottomley, who's on the board of the Linux Foundation and chairs its Technical Advisory Board, says almost all of Linux 3.8, which has been out now for a couple of months, is its technology and that Red Hat and Ubuntu, the two most popular Linux distributions, are moving to 3.8 with their next cut.

Containers can also be orchestrated orders of magnitude faster than hypervisors and come with the tools and controls for solving the application tenancy problem pretty easily. All this from a single image.

Naturally Parallels has a Cloud Server that it sells to hosting providers and naturally the thing has containers to isolate their apps, which increases uptime and offers improved performance, user experience and cost efficiency but to please everybody it also includes Parallels Hypervisor.

More Stories By Maureen O'Gara

Maureen O'Gara the most read technology reporter for the past 20 years, is the Cloud Computing and Virtualization News Desk editor of SYS-CON Media. She is the publisher of famous "Billygrams" and the editor-in-chief of "Client/Server News" for more than a decade. One of the most respected technology reporters in the business, Maureen can be reached by email at maureen(at)sys-con.com or paperboy(at)g2news.com, and by phone at 516 759-7025. Twitter: @MaureenOGara

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