[openstack-dev] Introducing the new OpenStack service for Containers

James Bottomley James.Bottomley at HansenPartnership.com
Tue Nov 19 18:02:45 UTC 2013

On Mon, 2013-11-18 at 14:28 -0800, Stuart Fox wrote:
> Hey all
> Not having been at the summit (maybe the next one), could somebody
> give a really short explanation as to why it needs to be a separate
> service?
> It sounds like it should fit within the Nova area. It is, after all,
> just another hypervisor type, or so it seems.

I can take a stab at this:  Firstly, a container is *not* a hypervisor.
Hypervisor based virtualisation is done at the hardware level (so with
hypervisors you boot a second kernel on top of the virtual hardware),
container based virtualisation is done at the OS (kernel) level (so all
containers share the same kernel ... and sometimes even huge chunks of
the OS). With recent advances in the Linux Kernel, we can make a
container behave like a hypervisor (full OS/IaaS virtualisation), but
quite a bit of the utility of containers is that they can do much more
than hypervisors, so they shouldn't be constrained by hypervisor APIs
(which are effectively virtual hardware APIs).

It is possible to extend the Nova APIs to control containers more fully,
but there was resistance do doing this on the grounds that it's
expanding the scope of Nova, hence the new project.


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