Wednesday, May 11, 2016

TIL From Users Today

I learn something about OpenStack each and every day and one of my broadest sources of OpenStack knowledge comes from my customers, the users of Time Warner Cable's OpenStack implementation.

Today, users' taught me, passively, by using it, about Shelving an instance. 

Suspending an instance puts it to sleep (via CPU suspension states) but the instance (virtual machines) is still using all of the memory and disk and cpu resources it was before (though the actual host CPU usage in this case is very very minimal.) Subtly different yet similar seems to be Pausing an instance. (I've never used this myself but am now checking to see if my users are using this.)

Stopping an instance still has the instance assigned to a hypervisor (essentially a compute host) and still "sort of" consumes resources on that host, most notably the ephemeral disk.

Shelving an instance makes a glance image snapshot of the instance and then removes all reference from the original hypervisor and compute host. It is consuming glance snapshot space in so doing but nothing on the hypervisor or compute host. So it is using the most minimal amount of resources possible.

Now to make this a real blog, I need to go add some links so that this is more shiny.