Re: [libvirt] Limit autostarting of domains to a few at a time.

On 11/05/12 13:32, Ruben Kerkhof wrote: > > Hi list, Hi Ruben,

> > I have about a hundred kvm vm's on a physical host, all marked as > autostart. > As soon as libvirtd starts up, all vms get started and they start > fighting for disk I/O. > Would it be possible to add an option to wait a while before starting > the next vm? > Batch-starting them in parallel, let's say 10 at a time, would be great > too. The problem with this is how to detect if the machine is actually started up. For libvirt the guests are black boxes and we don't have insight if the guest has already started up. There are a few options how we could detect this, but none of them are ideal: 1) wait until I/O load calms down - this is impossible with I/O heavy guests

2) use guest agent - no way to know if it has actually started/is installed 3) wait a certain amount of time - some guests take longer to start

> > I know I could use the libvirt-guest init script to do this, but we > rely on the autostart property for several purposes. The libvirt-guests script isn't 100% ideal for this purpose. It has the ability to re-start guests that were shut down by it, but can't be configured to start arbitrary guests. Unfortunately autostarting of guest can't be disabled in the daemon. If it was possible you could "virsh list --uuid --inactive --autostart" guests that need to be autostarted and use the function from libvirt-guests that is used to start the machines to do so (instead of reading them from the save-file).

This would still use the non-ideal approach (3) to rate-limit the starting. With the knowledge of the guest, this could be improved. As of the ability to disable autostarting, I'll have a look if it's hard to implement. I think this would make sense to have it as a config option. On the other hand, there's no ideal way to implement the detection of the end-of-boot event on the guest, so it'll probably be better to leave piece of functionality to be implemented by the users who know their infrastructure. Until then, you'll have either to start them via libvirt-autostart without the ability to rate-limit starting or note the autostart state into some other element (eg. the <metadata> element) and have a custom script that starts the guests.

> > Kind regards, > > Ruben Kerkhof > Peter