Don't default adding MIMEBOUNDARY headers when a mixed instances policy is set

[KashifSaadat]

Currently the MIMEBOUNDARY header is added if one of the following cases is met:

• AdditionalUserData is set on an Instance Group
• MixedInstancesPolicy is set on an Instance Group

The latter being set on an IG for a CoreOS nodepool now breaks on provisioning the nodes, as CoreOS doesn't support MIME messages. It is still set as required when AdditionalUserData has been provided, but will need follow-up with further investigation to get additional user data scripts working when using CoreOS.

• Regressed in Fix issue #6700: User Data for launch templates & other terraform issues #6732 for CoreOS
• Fixes remove MixedInstancesPolicy from nodeup MIMEBOUNDARY #7091

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[gambol99]

/lgtm

[gambol99]

/lgtm

[edsonmarquezani]

@KashifSaadat Thanks a lot for this! I've been waiting for it since 1.12 alpha, with Kops frozen because I use CoreOS and MixedInstancePolicy.

I opened this issue but haven't received any return since then. #6863

[KashifSaadat]

@edsonmarquezani no worries at all, sorry it took so long to fix!

[justinsb]

Thanks for fixing @KashifSaadat

Should we cherry pick all the way back to 1.12?

[justinsb]

I sent #7418 to cherry-pick to 1.14, as we want to cut a 1.14 beta soon!

[KashifSaadat]

Awesome thanks! I'll review and LG :)

[edsonmarquezani]

@justinsb A cherry-pick from 1.12.x ahead would be welcome, since I don't need to jump right to 1.14, skipping 1.13. Not sure if this is completely safe.

[KashifSaadat]

Ah missed your previous message, yes it may be good to cherry-pick back for those using the older kops releases 👍