Add NodeExporter dnsPolicy option.

[kahirokunn]

What does this PR change?

I have taken the actions described in the following document.

Pods running with hostNetwork, you should explicitly set its DNS policy to "ClusterFirstWithHostNet".

https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#pod-s-dns-policy

Does this PR rely on any other PRs?

How does this PR impact users? (This is the kind of thing that goes in release notes!)

Links to Issues or ZD tickets this PR addresses or fixes

How was this PR tested?

on local machine

Have you made an update to documentation?

yes

[Adam-Stack-PM]

@kahirokunn, Thanks for this PR. We will get this routed to an engineer for review very soon.

Please note this it may take a few days as our team is traveling to a company event this week.

CC: @allyleonce

[thomasvn]

Thanks for the PR @kahirokunn! I believe the default configuration for node-exporter does not include hostNetwork: true. Therefore, node-exporter should be defaulting to the default dnsPolicy and not ClusterFirstWithHostNet?

[kahirokunn]

@thomasvn default configuration for node-exporter include hostNetwork: true.

[thomasvn]

Ah, thanks for pointing me to that @kahirokunn! Yes, so I agree that updating node-exporter to dnsPolicy: ClusterFirstWithHostNet would be in alignment with the k8s docs.

Can you think of a way to test this change? Would it be worthwhile running nslookup in the node-exporter pod before and after the change?

[kahirokunn]

It works well in my environment, so I don't think it is necessary to go that far.

[thomasvn]

@kahirokunn I’ve tested in my environment and also see no issue with metrics emitted by node-exporter, and Prometheus scraping node-exporter. Approving as these changes are in accordance to k8s docs.