Configure CoreDNS and kubelet for dual stack DNS

[pschichtel]

Description

Previously the kube-dns service only received the primary IP address and the service was single stack. It is now configured with 2 address and address families and PreferDualStack (maybe that should be require?). To utilize the IP addresses, kubelet's config now also includes both IP addresses when running in dual stack mode.

Doesn't fix, but is related to: #7186

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• Manual test
• Auto test added

Checklist

• My code follows the style guidelines of this project
• My commit messages are signed-off
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

[jnummelin]

PreferDualStack (maybe that should be require?)

hmm, in this case I don't think there's much of a difference. In our case we know when things are dual-stack. This is what kube docs say, so if I read that correctly both Prefer.. and Require... behave exact same in our case.

PreferDualStack: Allocates both IPv4 and IPv6 cluster IPs for the Service when dual-stack is enabled. If dual-stack is not enabled or supported, it falls back to single-stack behavior.

[pschichtel]

yeah that's how I interpreted the docs as well. I went with "prefer" only for the remote chance of the service somehow being misaligned with the cluster dualstack configuration and then being blocked because it is RequireDualStack but doesn't have/receive an IPv6. not sure if that is ever a realistic scenario.

[pschichtel]

@twz123 Removing DNSAddress() revealed that this field is unused, which is kinda concerning.

[github-actions]

This pull request has merge conflicts that need to be resolved.

[pschichtel]

I'll rebase in the evening.

Any input regarding the unused calico fields?

[pschichtel]

Is there still a chance this could land for 1.36 or 1.36.1?

[pschichtel]

Fixed the failing test and rebased.

[twz123]

Is there still a chance this could land for 1.36 or 1.36.1?

I guess we can backport this.