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Re: cluster dns



https://github.com/openshift/origin/pull/9469 should resolve both
items but it's not in 1.2 codebases. It should be in the latest 1.3
alpha.

On Fri, Aug 12, 2016 at 4:37 AM, James Eckersall <james jeckersall co uk> wrote:
> Hi,
>
> I believe I've identified a couple of bugs, but would like to ask for other
> opinions before raising them officially.  These might also be more related
> to Kubernetes than Openshift.
>
>
> First one:
>
> We have a cluster running Openshift Origin v1.2.1 with kubernetes
> v1.2.0-36-g4a3f9c5.  This cluster has 3 masters and 4+ nodes.
>
> We've noticed that if we take master01 offline for maintenance, DNS lookups
> inside the cluster are affected.  It only affects lookups to the 172.30.0.1
> cluster IP which translates to 53 tcp/udp on the three masters.  Due to the
> iptables rules using the probability module, 1 in 3 DNS lookups fails as it
> is directed to the offline master.  I guess what's really needed here is for
> the master to be removed from the service endpoint so that the iptables
> rules are amended to prevent traffic hitting a master that isn't working.  I
> would like to see healthchecks here too.
>
>
> Second one:
>
> This cluster is running Openshift Origin v1.3.0-alpha.2+3da4944 with
> kubernetes v1.3.0+57fb9ac.  Again 3 masters and a bunch (~20) nodes.
>
> The first bug also applies to this cluster but the behaviour is somewhat
> different due to the introduction of iptables recent module rules.  I'm not
> 100% clear on the behaviour of this, but what seems to happen is that the
> first "recent" rule is always matched and hence all traffic from internal
> pods to cluster IP's always hits the first endpoint.  This means that ~100%
> of all DNS lookups against service names fail from other pods while master01
> is down.
>
>
> If anyone has any information to share on this, I'd be grateful. I can also
> provide further details if required.
>
>
> Thanks
>
>
> J
>
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