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LXC is the core technology, and the part that's actually revolutionary (for linux).

LXC is not really revolutionary, OpenVZ and Linux-VServer provided linux containerization for many many years.

I expect someone to come along any minute now and say that Docker no longer uses LXC anyway, now it uses libcontainer. This isn't true, libcontainer is just another frontend to LXC, libvirt being the first project to run a LXC without using the LXC userland.

http://linux-vserver.org/

http://openvz.org/

You forgot to name OpenVZ too, that is older than Solaris Zones. And Docker is originally based on LXC, that have several years. But is more than just containers, the layered copy-on-write union filesystem have a lot of practical advantages, the git-like repository for images redefines app packaging and the simple api is flexible enough to spawn a lot of projects that improved the ecosystem a lot in the last year.

If you're using only Linux, you may want to consider http://openvz.org/ . It's quite fast as compared to other virtualization software.

OpenVZ is very much like jails for Linux. I introduced it at my job four years ago and we've been using it ever since. I can attest to the savings in hardware overhead and in sysadmin time, compared to the alternatives of either full-blown VMs or all-services-in-one-Linux-box.

Nowadays there is also LXC, which supposedly is the future for Linux jails, seeing as their patch-set got into the mainline kernel—something OpenVZ failed to achieve. But IMHO LXC is not as stable and reliable as OpenVZ, nor as well-isolated by default, which is an aspect that is too often neglected.

Um, thanks for sharing your ignorance.

First hit on google http://wiki.openvz.org/Asterisk_from_source

Yes, which is what operating-system-level virtualization, which is basically an extension of the old concept of chroots or jails, is intended to do: give you many of the benefits of virtualization without the overhead of having multiple full copies of the OS running. It can also manage some resources better, e.g. having a unified filesystem cache. OpenVZ is Linux's approach.

However, full virtualization, like Xen, is somewhat more rock-solid in its separation of the virtual machines, and also allows more flexibility, in that each of the virtualized OSs can be different (don't even have to all be Linux, or if they are, can run different kernels/modules).

Sun had a great history but they just aren't as relevant anymore, there is little they have that redhat ( for example ) don't.

Solaris has two features compelling to me: Zones and ZFS.

The lack of a comparable feature to Zones (or even FreeBSD jails) in the mainline Linux kernel / major distributions is disappointing. There's OpenVZ, which I like and use, but it's a fairly significant patch on top of the Linux kernel. They don't track the mainline Linux kernel (which doesn't both me; I run CentOS 5).

OpenVZ is often overlooked for this kind of workload. _Kind_ of similar to a jail environment. We use it for a lot of "light" servers - project websites, that kind of thing but it will handle a lot more than that. http://wiki.openvz.org/Main_Page . Easy to install, really easy to configure & manage.

Actually, Xen is not at all similar to a BSD jail, no matter how you look at it. Xen does full OS virtualization from the kernel and drivers on down to userland. A FreeBSD is basically chroot on steroids. The "virtualized" processes run exactly the same as "native" ones, they just have some restrictions on their system calls, that's all.

Precisely.

Similar products in the Linux space are Linux Vserver (which I use) and OpenVZ.

Or Linux containers for that matter.

(Or for something more mature today, but implemented as a large out-of-tree patch, OpenVZ)

If you want to run linux processes with isolation from your physical machine, install an OpenVZ enabled kernel plus the openvz packages. It nicely isolates processes running inside each container; there is minimal virtualisation overhead (so you don't need a bigger machine).

Also the container root filesystem is an ordinary directory on your host. This means you can put multiple containers into a large filesystem and they share the available space, you can backup or copy containers trivially, and you can extend or reduce the amount of space available in the root filesystem while the container is running.

The amount of storage used per instance depends on your distro size; I start each instance with a minimal set of debian packages from a template occupying about 200 megs, and install more from there.

www.openvz.org.

Zones. Because sometimes full-blown virtualisation is too much like hard work

On Linux you get the same functionalty from OpenVZ or its commercial cousin Virtuozzo.

Besides i can easily host my own browsersettings on my home computer, in fact, i'll be setting it up (or trying to) when i come home

My thoughts pretty much. Host your own server for your own use. I can see this as a fantastic OpenVZ Template to easily deploy a server for anyone wanting one. You can get a VPS for around $10/mo if you really wish to keep it in your own hands, I know I would, and I bet many others would opt if that option was available.

Yes, they are all very different but at the same time quite similar from a user's perspective. All of them (unless I've missed something) more or less emulate a whole machine. This means you have to mess with disk images or dedicated drives/partitions/LVs, allocate a fixed amount of RAM to the guest, among other things.

Personally I like the approach of OpenVZ and VServer better. The main OS and the guests all share the same kernel, share the RAM and their root filesystems can be just subdirectories of the host's filesystem. When inside the virtual server you don't realize that though. You only see your own processes and everything works as if it was a dedicated server. You can run iptables, reboot and just about everything you could normally do in XEN/KVM/VMWare. Including live migration of virtual servers to other physical hosts. chroot on steroids.

I really hope OpenVZ and/or VServer will be merged at some point. VServer seem to keep up with current kernel releases so that wouldn't be too hard to merge I guess. OpenVZ usually have a lag of something like half a year.

--Look into virtualization. OpenVZ is doing some interesting things with Linux -> Linux VMs (or VE's, in their terminology.)

http://wiki.openvz.org/Download_live_CD

Xen trades off performance for much better isolation and security.

I guess I have to correct you here. Xen trades off performance for an ability to run different kernels, and this has nothing to do with either isolation or security. So, Xen is good when you want to run different kernels (different OSs).

OpenVZ, on the other hand, employs a single kernel model, which makes it suitable for you if you only want to run Linux (different distros are possible, different kernels are not). But in this very field OpenVZ is way better than Xen -- not only in terms of performance, but also scalability, manageability, density, and usability.

Speaking of isolation and security, OpenVZ runs on thousands of ISP/HSP servers, and everyone can buy a VE (Virtual Environment) for about 10-15 bucks a month. There one have a root account and can try to exploit the system in all the possible ways. So far those HSPs are not out of business yet, that practically proves the system is secure and properly isolated. More to say, security comes from the constant care, and we (OpenVZ team) do care for security a lot, see this blog entry for some more details.

OpenVZ is ok if all of your child environments run the same OS and you don't care about them stealing each other's resources.

xen can do a lot of what zones do, albeit much less efficiently

Of course VMware and Xen are going to be slow - that is the tradeoff you get when you want the ability to run both Windows and Linux at the same time.

http://openvz.org/ - it does a much better job of virtualizing IMO. The only minus is that all VM's have to use the same kernel version.

From the article: "When quizzed on Microsoft's plans, Mr. Ballmer replied, "Our view is that virtualization is something that should be built into the operating system.""

Virtualization belongs below the operating system, let's say in the BIOS.

that depends on what kind of virtualization you want. there are differnet kinds, based on what you want to do.

i think that he is saying that you should run your virtualization stuff at the os level, ala openVZ.

i guess it goes without saying that "virtualization" is *such* an overloaded term now a days that you can never be sure what anyone is talking about anymore.

in a nutshell, OS level virtualization (according to the these folks) means that the OS itself is virtualized instead of the hardware which is the vmware/ms virtual server way. OS level virtualization means that you run one OS, and each virtual environment is a container with a "private" instance of that OS... like a root jail on steroids.

what you end up with is a bunch of instances of the same OS. the virtual servers are shielded from eachother, and the host shielded from the virtual servers, but the virtual servers are not necessarily shielded from the host. the key difference is that all of them, virtual server and host alike, are running the same kernel. they don't run copies of the same kernel, they all talk to the same running kernel. this means simpler setup and administration and more efficient use of disk, cpu and memory thanks to reduced redundancy in hardware and operating system emulation and/or abstraction. openVZ pretty much lets you run a bunch of iterations of the same OS, but with different applications, users, IPs, etc.

you essentially are giving up the ability to run arbitrary guest OS's in exchange for simpler configuration and more efficient use of resources.

it seems to me that OS level virtualization (instead of hardware/hypervisor virtualization) is more along the lines of what MS would want, which is people buying lots of windows licenses, or just paying up for the most expensive version of windows so they can virtualize to the fullest extent of their hardware's capabilities.

i think that this might be the first step to competing with VMWare and all the others that let you run windows servers on linux. one way to improve stability in anything is to reduce the number of things that it does. the weird language in vista about using licenses in virtualization might be the precursor to the different tiers for the next iteration of windows server where buying the top level OS grants you the licensing freedom to many virtualized servers on the same machine.

what will be most interesting is if active directory and the like will change... will you still be required you to run DNS and other services on your AD server? or, will you be able to off load those services to "smaller" single function virtual servers?

Xen
VMWare
linux-vserver
UML
OpenVZ
Plex86
Qemu
Bochs
lhype

and now

KVM

http://linuxvirtualization.com/ has some good linux to recent announcements regarding virtualisation software on Linux.

Are there any more?

Here are some typical usage scenarios for OS-level virtualization; server consolidation is number one I believe. All that also applies to Xen and VMware (although their overhead in those cases would be higher); in addition, they can run *different* operating systems on the same box -- this is what OpenVZ don't do.

OpenVZ is an OS-level virtualisation -- this is quite different technology from that of Xen and VMware. OpenVZ provides separate isolated containers within a *single* kernel image, while Xen makes possible to run *different* kernels on the same piece of hardware. More info about those differences is here; the only thing I want to add is VMware is moving into Xen direction.

Xen was a big hype last year, but more virtualization products for Linux come to light, including OpenVZ, others. It is not just about Xen or VMware anymore. In fact, kernel developers work on a common interface for paravirtualization software. That means users are going to have more choice implementing their kernel containers, whether XenSource stabilizes their product or not.

Linux & UNIX based virtualization has always been far superior to that of Windows. Superior is probably an understatement though, more like exponentially better.

Just check into

OpenVZ http://openvz.org/
FreeBSD Jails http://en.wikipedia.org/wiki/FreeBSD_Jail
Solaris zones http://www.opensolaris.org/os/community/zones/faq/
Xen http://www.cl.cam.ac.uk/Research/SRG/netos/xen/

and the list goes on. So much better on *nix. Of course, I think that is somehow related to the fact you can run a *nix box via CLI, bare minimum of functionality, the likes of which it even the best Windows gurus cannot get close to (though Mark Russinovich and Bryce Cogswell do rox)

What is funny, is so many of us are ignorant of virtualization's roots in IBM mainframes. Big Blue was so far ahead of the times, it is like omg. BTW, I love Wikipedia. I've been preparing a presentation on virtualization the last few days, and Wikipedia makes it so easy!

OpenVZ, which is a subset of the commercial Virtuozzo product, is being lobbyed for inclusion in the kernel.

Although Xen requires patching of the kernel, it is the best performing open source virtualization layer at present.

Thanks!

Speaking of "recentness", current development branch of OpenVZ kernel is 2.6.16 based (here). You can actually use it, but we can not guarantee it is as stable and matured as the current stable 2.6.8-based kernel.

Speaking of complexity, it is indeed complex. Any OS is complex. VMWare itself is very complex. Any stuff that is not trivial is complex.

The questions are: whether it works, and is it maintainable?

Whether it works? OpenVZ and Virtuozzo works just fine -- ask anybody who's using it, get a cheap Virtuozzo VPS from one of the HSP, or just install it on your Linux box and see for yourself.

Is it maintainable? OpenVZ stable kernel is based on Linux kernel 2.6.8 (with tons of backported fixes and driver updates). We have recently ported it to 2.6.15 and 2.6.16, and also to the kernels from Fedora Core 5 (here) and SUSE 10 (here). So I think it is maintaintable.

[VMWare] has some performance issues, and Xen's paravirtualization gets a fine balance, that is to have a minimal set of modification of the guest OS.

Hmm, isn't that Xen which requires a modified Linux kernel? Is that "a minimal set of modifications"? Are you kidding? In contrast, in OpenVZ's VE you run an unmodified Linux distribution, the only missing piece is the kernel which is provided by the host OS. There are modifications (like removing getty from /etc/inittab), but they are not strictly required.

What's the point then? OpenVZ also runs a modified Linux kernel. Well, the point is you can not have hundreds of VMs with Xen (or VMWare), but you can -- with OpenVZ. OpenVZ is also more stable -- but Xen will cure this, I believe, so this is not the point in the long term.

Basically, VMWare is at the one end of the scale -- can run anything, bad performance, scalability and density, OpenVZ is on the other end -- can run Linux 2.6 only, native performance, best possible scalability and density, easier management. Xen is somewhere in the middle of all this.

Speaking of complexity, it is indeed complex. Any OS is complex. VMWare itself is very complex. Any stuff that is not trivial is complex.

The questions are: whether it works, and is it maintainable?

Whether it works? OpenVZ and Virtuozzo works just fine -- ask anybody who's using it, get a cheap Virtuozzo VPS from one of the HSP, or just install it on your Linux box and see for yourself.

Is it maintainable? OpenVZ stable kernel is based on Linux kernel 2.6.8 (with tons of backported fixes and driver updates). We have recently ported it to 2.6.15 and 2.6.16, and also to the kernels from Fedora Core 5 (here) and SUSE 10 (here). So I think it is maintaintable.

[VMWare] has some performance issues, and Xen's paravirtualization gets a fine balance, that is to have a minimal set of modification of the guest OS.

Hmm, isn't that Xen which requires a modified Linux kernel? Is that "a minimal set of modifications"? Are you kidding? In contrast, in OpenVZ's VE you run an unmodified Linux distribution, the only missing piece is the kernel which is provided by the host OS. There are modifications (like removing getty from /etc/inittab), but they are not strictly required.

What's the point then? OpenVZ also runs a modified Linux kernel. Well, the point is you can not have hundreds of VMs with Xen (or VMWare), but you can -- with OpenVZ. OpenVZ is also more stable -- but Xen will cure this, I believe, so this is not the point in the long term.

Basically, VMWare is at the one end of the scale -- can run anything, bad performance, scalability and density, OpenVZ is on the other end -- can run Linux 2.6 only, native performance, best possible scalability and density, easier management. Xen is somewhere in the middle of all this.

Have you actually read the interview?

OpenVZ provides a kind of virtualization called OS-level virt, or partitioning, or slicing. Basically you divide your Linux box into multiple small linux boxes, called virtual environments (VEs).

In each VE you can have different Linux distro installed. Consider FC4, FC5, CentOS and Debian running on the same box, so you can compile and test you app in all these distros, without a need to reboot or have a dedicated boxes for each of those.

To further understand between three different kinds of virtualization, read this small article

Have you actually read the interview?

OpenVZ provides a kind of virtualization called OS-level virt, or partitioning, or slicing. Basically you divide your Linux box into multiple small linux boxes, called virtual environments (VEs).

In each VE you can have different Linux distro installed. Consider FC4, FC5, CentOS and Debian running on the same box, so you can compile and test you app in all these distros, without a need to reboot or have a dedicated boxes for each of those.

To further understand between three different kinds of virtualization, read this small article

If you are so happy with Xen, I suggest you try OpenVZ (http://openvz.org/ -- I bet you'll be even more happy. Unlike Xen, OpenVZ does not have that big I/O overhead (our tests shows Xen guests do I/O about 30% slower than native system). The biggest thing though is you can run not 3 but 30 virtual environments, and dynamically manage their resources (like adding/removing memory from the environment without any need to restart it).

Finally, live migration for OpenVZ will be released Real Soon Now.

If you need to run Linux on Linux, take a look at OpenVZ -- compared to VMware, it has *much* higher scalability and lower overhead. And it *is* stable.

In short, OpenVZ uses the single-kernel virtualization approach, which differs from either VMware or Xen: instead of trying to emulate something, kernel is modified to support multiple isolated environments, so each such environment looks-and-feels like a separate server. Good things about it is (1) best possible performance (no to little performance overhead due) and (2) hardware resources (CPU, RAM etc.) are controlled from within a single kernel, so resources are used most effectively.

Although Virtuozzo is "built on top of OpenVZ", is Virtuozzo's kernel component a publicly available version of OpenVZ, built without using any proprietary patches or modules?

http://openvz.org/documentation/tech/virtuozzo states "Differently from OpenVZ, Virtuozzo(TM) is developed and designed to run production workloads in 24×7 environments ..."

and goes on to list, among Virtuozzo's advantages over OpenVZ:

"Higher VPS density. Virtuozzo(TM) provides efficient memory and file sharing mechanisms enabling higher VPS density and better performance of VPSs.

"Improved Stability, Scalability, and Performance. Virtuozzo(TM) is designed to run 24×7 environments with production workloads on hosts with up-to 32 CPUs."

Why should Linux accept a kernel patch if (unlike Linux itself) it is not designed to run 24×7 environments with production workloads on hosts with up-to 32 CPUs?

From: the website

Second technique: Para-Virtualized Machines. This technique also requires a VMM, but most of its work is performed in the Guest OS code, which in turn is modified to support this VMM and avoid unnecessary use of privileged instructions. The paravirtualization technique also enables running different OSs on a single server, but requires them to be ported. The paravirtualization approach is used by Xen, UML.

Third technique: Virtualization on the OS Level. Most applications running on a server can easily share a machine with others, if they could be isolated and secured. Further, in most situations, different operating systems are not required on the same server, merely multiple instances of a single Operating System. OS Virtualization systems have been designed to provide the required isolation and security to run multiple applications or copies of the same (or similar i.e different Linuxes) OS on the same server. OpenVZ, Linux VServer are examples of OS virtualization.