Re: [libvirt] KVM processes -- should we be able to attach them to the libvirtd process?

Daniel P. Berrange wrote: > On Tue, May 05, 2009 at 04:13:38PM -0400, Hugh O. Brock wrote: >> Not too long ago we took a patch that allowed QEMU VMs to keep running >> even if libvirtd died or was restarted. >> >> I was talking to Matt Farrellee (cc'd) this afternoon about >> manageability, and he feels fairly strongly that this behavior should be >> optional -- in other words, it should be possible to guarantee that if >> libvirtd dies, it will take all the VMs with the "die-with-libvirtd" >> flag set down with it. >> >> I'm not sure this API is portable to Xen, but it would work on any >> hypervisor that represents the VM as a normal process. >> >> Does this strike anyone else as useful behavior? > > This isn't really a model we want in the architecture. That the QEMU > instances used to die when libvirtd died was an unfortunate artifact > of the fact that QEMU was the parent process leader. These days all VMs > are fully daemonized, so there is no parent/child relationship. In fact > QEMU was really the odd-ball in this respect, because with Xen/OpenVZ/LXC > and VirtualBox, VMs have always happily continued when libvirtd stopped > or died, as do storage pools and virtual networks. > > This is important because it ensures we can automatically restart the > libvirtd daemon during RPM upgrades, and provides robustness should a > bug cause the daemon to crash - the daemon can be trivially restarted > and continue with no interruption to services being managed. > It doesn't appear to be the case that the libvirtd daemon can trivially restart and continue with no interruptions. Right now it loses track of VMs.

In a scenario where VMs are not deployed and locked to specific physical nodes, it can be highly valuable to have ways to ensure a VM is no longer running when a layer of its management stops functioning.