Changing the required virtio-rng sources on an existing cluster is potentially a dangerous thing. If one by mistake require hwrng when no host have it configured properly means that all hosts immediately go Non-Operational. We should prevent these simple mistakes by one-time check of all the hosts in the cluster and don't proceed (to override this check one can move the offending host to Maintenance...I'd check only for "Up" hosts)
Can you please provide verification scenario?
when the change of parameter would cause host to go non-operational you would now get a warning before proceeding. One example is you edit cluster and newly require hwrng source, and one or more "Up" hosts in the cluster do not have it available. Today upon saving Cluster changes those hosts immediately go non-operational, now you will know beforehand:)
@Nisim additionally to the "Up" hosts, the UI should report warning for all hosts in the cluster. This is done so the user would have information about missing capabilities also for hosts in e.g. maintenance mode. So the UI warning should list all hosts that fail given check.
Verification build: rhevm-3.6.0-0.18.el6 host RHEL 7.2 (rng is suuported from 6.6 and above) sanlock-3.2.4-1.el7.x86_64 qemu-kvm-rhev-2.3.0-28.el7.x86_64 vdsm-4.17.8-1.el7ev.noarch libvirt-client-1.2.17-5.el7.x86_64 Verification scenario: 1. Have 2 hosts under the same cluscter. 2. Edit cluster and enable /dev/hwrng. click ok. 3. Verify Confirmation pop-up message appears: Confirm Cluster Edit The following hosts may become non-operational under specified configuration: Due to unsupported /dev/hwrng source: host_2 Are you sure you want to continue? 4. click ok. 5. Remove one of the hosts that become unreachable and add it again. 6. Run VM under this host, from VM run the command lsof /dev/random verify host is now supporting hwrng. Test case for verifying pop-up message created.
oVirt 3.6.0 has been released on November 4th, 2015 and should fix this issue. If problems still persist, please open a new BZ and reference this one.