[ovirt-users] oVirt engine and primary DNS

Gianluca Cecchi gianluca.cecchi at gmail.com
Thu Oct 27 10:48:33 UTC 2016

On Thu, Oct 27, 2016 at 12:32 PM, Jonas Israelsson <
jonas.israelsson at elementary.se> wrote:

> I could indeed, the issue I saw yesterday is resolved already. I was
> merely thinking we might have a potential single point of failure here.
> While the primary nameserver was offline the machine (where the
> ovirt-engine is running) itself had no problem doing name-resolution, still
> oVirt-ui was acting rather unpleasant.
> And since my changes to resolv.conf only had an impact after restarting
> the engine I thought there are some internals, such as a cache causing this
> problem.

It was only a suggestion, I didn't try myself with ovirt-engine.
But if you have a test system, you can simulate running something like this
on your engine server

change resolv.conf while engine is running

silently drop connections to primary dns server with
iptables -I OUTPUT -d your_primary_dns_ip -j DROP
(at the end of tests you delete the rule checking the line number of the
inserted line (it should be 1 because of "-I" option above) with
iptables -L -n --line-numbers
and then
iptables -D OUTPUT 1
or in general
iptables -D OUTPUT N
if line is not 1 but N

you can then monitor calls to dns with tcpdump, something like
tcpdump -nn dst port 53

HIH debugging,
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