fix(plan): explicitly check for CNAME conflicts

[wbh1]

Description

This fixes a bug introduced in v0.13.5 (via this PR) in which CNAMEs are no longer treated as another candidate for the same DNS name. Instead, they are their own line in the plan and will always try to be created. Consequently, the plan can result in both A records (or others) and CNAMEs attempting to be created simultaneously, which results in errors.

Previously, it would put a CNAME and A record as candidates to the same domain (e.g. nginx.lke.hegedus.wtf), then ResolveCreate would choose which record to create (explicitly preferring A records as of #2716).

You can see how the data structure changed based on these screenshots from my debugger on v0.13.4 vs v0.13.5 (and main).

Old:

New:

Previously, just the DNS name was the key in the map, but now both the record type and the set identifier are considered part of the key.

Rather than reverting that change or further altering the data structure, I decided to implement the necessary CNAME safeguarding to avoid conflicting records. It feels gross to range over the same data structure multiple times like this, but it ought to always be small enough that it has a negligible impact on performance. Open to suggestions, though.

There are a lot of issues I've found related to trying to create CNAMEs instead of A records since v0.13.5. Some of the ones I found in passing that I think this might address:

Fixes #3714
Maybe #3833
Maybe #3787
Maybe #3706

This is another bug related to the data structure change to use planKey, but I don't think this solves it: #3715

Checklist

• Unit tests updated
• End user documentation updated

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[wbh1]

This may already be covered by #3747, but perhaps @johngmyers or @cronik could speak to that.

[mloiseleur]

Hello @wbh1,

Thanks for this PR. Would you please add a test to this PR ?

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[johngmyers]

This PR is unlikely to move forward as it duplicates #3747

[wbh1]

Closing in favor of #3747, which was merged.