Great, thanks for clarification. ---- On Thu, 25 Oct 2018 13:07:58 +0100 Simone
Tiraboschi <[email protected]> wrote ---- On Thu, Oct 25, 2018 at 1:31 PM
Alan G <[email protected]> wrote: Hi, I have 4.1 cluster with FC block
storage and hosted engine. Last night a host went unreachable due to a
driver/firmware issue with the NIC card. The Engine spotted this, the host was
fenced and everything behaved as expected. However, it got me thinking - if the
affected host had been the one running the Engine, what would have happened?
I'm assuming the Engine would have failed liveness check on the other hosted
engine hosts and they would attempt to start the Engine. But as the "failed"
host still had access to the storage (I believe the HBA was still working) then
they would not be able to get a lock on the storage. In which case I'm in a
catch-22, the Engine cannot fence the failed host because its network is
isolated, but the Engine cannot be restarted else where until the failed host
is fenced. At this point it requires human intervention to fence the failed
host. Is my understanding correct on this? If so is there any way to mitigate
this risk? ovirt-ha-agent implements a specific test for this kind of failures
continuously trying to ping a specific IPv4 address (usually the network
gateway) to check network connectivity on each involved host. On failed pings
each host penalises itself by a certain amount of points; the HA score of each
host is written into the hosted-engine metadata volume on the shared storage so
each host can also see the score of other hosts and in your case this would
work since all the hosts can still access the storage via FC. Once the
difference between the score of the host running the engine VM and the best
candidate host is large enough a migrate to best host (or shutdown and restart
there if not possible as in your case) action will be triggered. If you want,
you can easily try to reproduce this scenario. Thanks, Alan
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