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Subscribe to this list via RSS Blog posts tagged in OSv

Next Generation High Density App Servers Don't Require Scrapping Your Hypervisor

Recently, I sat in a conference session extolling the seemingly endless virtues of Linux Containers.  I heard claims that hypervisors were old hat: ancient bloated engines which rely on inefficient replication of a large operating system stack in order to serve up applications.  The speaker painted a picture of a future where hundreds of applications are virtualized on each piece of hardware.  "What is really needed," glowed the speaker, "is a lightweight, efficient means of serving up application: containers."

Containers are cool, but not a panacea

Containers share the same kernel as the host, so they are not burdened with the extra memory and CPU cycles it costs to replicate a full operating system stack in a hypervisor scenario.  Compared to hypervisor-generated virtual machines, containers can be fast and lean.  But they are also limited.  

Since Linux containers share the same kernel as the host, it is impossible to run Windows.  Or FreeBSD. Or NetBSD.   Or another version of the Linux kernel.  Or another Linux distribution which requires a different kernel.  All of those scenarios are best handled by a real hypervisor.  And the security aspect of hypervisors is huge, worthy of a separate blog entry of its own.  Still, if you need an environment within your organization where many workloads can leverage a single kernel environment, containers can be a viable solution.

However, some of the most vocal container advocates insist that these problems relating to containers are really application problems in disguise.  Issues about kernel support and security are the results of improper application design, they claim.  When we raise the bar on applications so that they are based solely on access to application servers, then the objections to containers will melt away -- and so will hypervisors, for the most part.  Or that's what some of these advocates claim, at least.

The death of the hypervisor is greatly exaggerated

But is there another scenario which could answer the call for highly responsive and lightweight virtual instances which does not use the container solution?  Maybe one that can actually leverage the flexibility and security which is part and parcel with most hypervisors?

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You may have heard the new buzz word “Cloud Operating System” in the last few months. The term gained prominence when Cloudius Systems launched OSv at LinuxCon in September. Many people working on OSv - namely Glauber Costa, Pekka Enberg, Avi Kivity and Christoph Hellwig - are well known in the Linux community, due to their role in creating KVM. But the concept of a cloud operating system isn’t new. There are many cloud OSes from which to choose, including the Xen Project's Mirage OS, which had its first release a few weeks ago.

Cloud Operating Systems: A New Incarnation of an Older Idea

The approach taken by OSv (as well as others before OSv), revisits an old approach to operating system construction - the Library OS - and puts it in the context of cloud computing within a virtual machine. The basic premise of this approach is to simplify the application stack in the cloud significantly, removing layers of abstraction and offering the promise of less complexity, increased system security and simplified management of application stacks in the cloud.

b2ap3_thumbnail_CloudOSDiagram.png
Figure 1: on the left, you see a typical application stack run in the cloud today. Of course this is a simplification (leaving out AWS or other cloud APIs). On the right you see. that Cloud Operating systems such as OSv remove the Operating System and replace it with a Language Runtime that is designed to cooperate with the virtual environment the Hypervisor provides (which may include access to Hypervisor APIs).

As you can see, Cloud Operating Systems are designed to run a single application within a single Virtual Machine: thus much of the functionality in a general purpose operating system is simply removed. In other words, you strip out everything that your language and APIs do not need and let the hypervisor take care of it: what you end up with a lean language specific software stack that runs much faster than a normal VM, and is more secure simply because there is less code that could be attacked.

Examples of Cloud Operating Systems

As stated earlier, OSv is not the first Cloud Operating System on the market. To the credit of OSv’s creators, it did put the technology on the map by creating lots of buzz.

Cloud OS

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Open@Citrix

Citrix supports the open source community via developer support and evangeslism. We have a number of developers and evangelists that participate actively in the open source community in Apache Cloudstack, OpenDaylight, Xen Project and XenServer. We also conduct educational activities via the Build A Cloud events held all over the world. 

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