Re: [libvirt-users] Create multiple domains from single saved domain state (is UUID/name fixed?)

Fair enough :) I just wanted to make sure it wasn't supported... I'm probably better off using QEMU directly. I totally understand that libvirt makes some sane decisions that makes sense for data center management. I'm not sure why it couldn't be done. But honestly hacking libvirt to violate a core invariant is probably asking for trouble :)

Den 19. apr. 2016 11.17 PM skrev "Martin Kletzander" <mkletzan(a)redhat.com&gt;: > On Tue, Apr 19, 2016 at 03:22:18PM -0700, Jonas Finnemann Jensen wrote: > >> >>> You'll also need to change the name and uuid of the domain at the very >>> least. >>> >> >> Agree, but is that possible with libvirt? >> >> > Not in a supported way. But you can, technically, edit the save file > (not using virsh), change the name and uuid and restore it. But don't > seek help when something doesn't work for you after that =) > > If you do that (restore a previously running image with a different MAC >> >>> address) >>> >> >> Yeah, probably I wouldn't change the MAC address. As I want to attach the >> VMs to different networks. >> I rely on the IP being in a different subnet to identify the VM in my >> metadata service. >> Using IP filters to enforce the subnet seems like the most robust way of >> being sure which VM I'm talking to. >> >> possibly by having the host toggle the interface offline and back on >> >> Yeah, I think unplugging the virtual network cable before I save the VM >> memory, and plugging it back in after I load the VM, then DHCP would run >> immediately. >> As an added benefit any guest program I have talking to my meta-data >> service would be able to detect that the VM has been loaded, by looking >> for >> network connection. >> >> >> -- >> Regards Jonas Finnemann Jensen. >> >> 2016-04-19 14:26 GMT-07:00 Laine Stump <laine(a)laine.org&gt;: >> >> (please don't top-post. Put your responses inline, in context) >>> >>> On 04/19/2016 01:09 PM, Jonas Finnemann Jensen wrote: >>> >>> virt-builder looks like some fancy guest/host interaction related to >>>> building VM images. >>>> >>>> What I'm looking for is more like: >>>> virsh save running_domain saved-domain-A.img >>>> cp saved-domain-A.img saved-domain-B.img >>>> virsh save-image-edit saved-domain-B.img // Change the network, >>>> possibly MAC, VNC port >>>> >>>> >>> You'll also need to change the name and uuid of the domain at the very >>> least. And I assume these will all be transient domains, not persistent. >>> >>> >>> Then in parallel I want to do: >>>> virsh restore saved-domain-A.img >>>> virsh restore saved-domain-B.img >>>> >>>> >>> If you do that (restore a previously running image with a different MAC >>> address), at the very least the guest OS will be confused about the MAC >>> address of the network card, and you'll very likely end up with both >>> guests >>> responding to ARP requests for the original MAC address. There's likely >>> other problems that I haven't thought of that will happen as well. >>> >>> >>> So that I have two instances of the same virtual machine starting from >>>> the same state. >>>> This way I can reset the VMs without having to reboot them (booting is >>>> rather slow). >>>> >>>> I practice I'll probably have ~16 instances at the same time. Constantly >>>> being reset to the same state. >>>> I tried with QEMU, and it's seems totally doable with savevm, copy file, >>>> then doing loadvm twice in parallel. >>>> (I'll be using a separate network for each VM, so I can be sure which >>>> one >>>> I'm talking to). >>>> >>>> >>> Well, as long as they're completely isolated from each other, you may >>> have >>> a better chance of success. However there will still be the issue of the >>> IP >>> address of the network interface. You can't have two networks using the >>> same IP range (since libvirt doesn't use network namespaces for its >>> networks), so the guest will need to change its IP, which means it will >>> need to be notified of this need, possibly by having the host toggle the >>> interface offline and back on - you can use virsh domif-setlink to do >>> this. >>> >>> >>> >>> Is this doable with libvirt, or am I better off using QEMU directly? and >>>> how? I couldn't do internal snapshots with --live, and snapshot-revert >>>> says >>>> it can't revert to external snapshots yet :) >>>> (using QEMU directly would certainly leave me with a lot of manual >>>> network configuration) >>>> >>>> >>> Someone else will have to talk about the particulars of snapshots... >>> >>> >>>