This is sort of similar to Q123566, but I want to add a few clarifications:

  • KVM is the Linux-kernel-based virtualization technology (specifically: a hypervisor) that underlies most non-Xen FOSS virtualization platforms/tools.
  • QEMU is an atomic tool/utility/program, that, today, fills the role that kvm(1) did while its eponymous hypervisor was under development. It is capable of using kvm(3) as an emulation backend; this is its most efficient mode of operation on x86_64-based platforms.
  • Neither of these are virtualization solutions in the way that ESXi and Hyper-V (which each pack their own, purpose-built, type-1 hypervisor) are.
    • A solution (not a tool or technology), whether developed in-house or acquired externally, is a crucial aspect of any enterprise IT deployment.

Clarifying that last point: a kernel module per se does not facilitate devops, nor does QEMU run itself. A tool is not a solution (though a sufficiently robust tool may lull a sysadmin into thinking their ad-hoc, in-house, undocumented solution is viable).

None but the most "confident" of sysadmins believe that an array of machines running manually-installed operating systems, configured by a (manually-administered) smattering of systemd.unit(5) files invoking various instances of qemu-system-x86_64(1), is sustainable or scalable.

That gap—that KVM (partly due to being a type 2 hypervisor) is the only "odd one out"; it's a hypervisor not locked to a particular tool and/or solution—is where Red Hat's virt-manager, comes in. It seems to be (aside from oVirt, apparently a layer-on-top-of / interface-to virt-manger,) the only enterprise-grade QEMU-based (and, by extension, KVM-based) virtualization solution currently on the market.

But whereas many companies use ESXi1 and Hyper-V2, it's hard to find any3 that use virt-manager. And while a handful of companies identify as using KVM-based solutions4, information on how KVM is actually used is scarce.

So, how is KVM used with enterprise workloads, which can't afford the assorted risks of running on a shoestring shell-script-and-SSH infrastructure? Is it used at all? Do companies just commandeer something like SaltStack to corral KVM+QEMU as part of an in-house solution? Is virt-manager actually in wide use but a well-kept secret? I can't figure out why there's this information-black-hole around what is apparently the virtualization solution powering Red Hat, Inc's (and nobody else's?) entire infrastructure.

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    Further compounding my confusion is the fact that this hypervisor is the only one privileged to be built-in to the kernel which, itself, underlies most virtualization as-implemented today, both host and guest sides... – JamesTheAwesomeDude May 12 at 22:46
  • I think this post is entirely off topic here as opinion based. Yes, some enterprises use Virt Manager. Also, Google Proxmox – davidgo May 13 at 3:18
  • @davidgo my question was very specific. Even if lots of companies (as I note in my post) claim to use it, the operative word in the title was how. – JamesTheAwesomeDude May 13 at 16:06
  • Also, Proxmox isn't a Google product- but I thought it runs Xen? [ETA: aha, it seems Proxmox is KVM-based; thanks for sharing!] – JamesTheAwesomeDude May 13 at 16:07

KVM is widely used in the cloud, both private and public:

KVM is "just" a hypervisor with an API, many companies build tools around it to make it easy to use. No one expects you to use KVM directly (although it is possible).

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  • OpenStack and OLVM are helpful contributions; thank you for those! Amazon isn't too keen on sharing details about their (internally-implemented?) KVM-based solution; if there were any details available about the stack they run, it'd be a relevant mention, though. – JamesTheAwesomeDude May 13 at 16:12

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