On 06/08/15 04:36 +0200, Noel Kuntze wrote: > I know that increasing the complexity reduces the availability of a > service, so it is no surprise to me that it is frowned upon running > services, which should be highgly available, on virtual machines. > > However, services are regularely run on VMs and HA is desired, even > if the only thing that should be "protected" against is the downtime > when the kernel needs to get upgraded or a daemon needs to be > restarted. > > So I think fence-virt has a use case. > My use case currently is to build a HA cluster of VMs, which > currently host a simple mirror for software packages. They're stored > on shared storage, which has a partition formatted with GFS2 on it. > I use pcs(d), pacemaker, corosync and fence-virt over a serial > device to fence hosts. > Obviously, a single serial connection I currently only have one > hypervisor, but could expand to more. > I'm doing this, because I want to write a doc about clustering on > Linux in the year 2015, so clustering on VMs is definitely a use > case that I will describe. > > I know that multicast should actually work in common use cases, but > I found that for some reason, the bridge device of the VMs don't > forward traffic for the default multicast group of fence-virt to the > other bridge ports, rendering it useless.
ISTR this is problematic in general[1], therefore I spelled "multicast-friendly" network out. [1] https://bugzilla.redhat.com/show_bug.cgi?id=880035 > I haven't dug deeper why that happens, but through Googling I found > that it's a common problem that bridge devices on Linux don't > forward some types of traffic. Obviously, if multicast works, one > can just relay multicast networks over several other interfaces to > relay requests. > > The man page of virt_fence.conf mentions "libvirt-qmf" as backend, > instead of "libvirt", which should be able to route fencing requests > to the correct host by using Apache QMF. I figure that's the correct > backend for such a purpose. Oh, forgot about this, good that it works for you. Actually it got discussed in the past [2] -- btw. could you provide an update to the recipe[3] (ask Andrew for the wiki account, or post it on-/off-list), please? [2] https://www.redhat.com/archives/linux-cluster/2013-June/msg00020.html [3] http://clusterlabs.org/wiki/Guest_Fencing#For_Guests_Running_on_Multiple_Hosts -- Jan (Poki)
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