Adding affinity and PDB to dns.

[michalschott]

Adds affinity and PDB to dns.

Several times had situation where kube-dns pods were scheduled on the same worker (including empheral instances) and during ie. rolling-updates / node termination / node drain events DNS was unresponsible for few seconds.

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[zetaab]

I have tried to get similar change through. However, some people are saying that if dns pods are not in same node the performance is really poor in large clusters. Anyways, I appreciate PR like this.

/ok-to-test

[zetaab]

This should be applied imo to coredns as well

[michalschott]

@zetaab core-dns manifest is also updated.

I'm aware about PodAffinity performance issues in large clusters but define large - 100+ workers? I'd assume a lot of people starts their k8s journey with KOPS in rather small clusters.

[zetaab]

@michalschott oh, I should maybe read the changes before saying anything :) I totally agree with you, most of the kops clusters are less than 50 nodes I would say.

/lgtm

[chrisz100]

Imho Cluster size and affinity is totally up to the user for me. As affinity is one of the core features of kubernetes I’m totally fine with using it. If that gets a performance issue people should scale their schedulers well
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chrisz100, michalschott

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[chrisz100]

/retest