✨ Add AWSMachines to back the EC2 instances in AWSMachinePools and AWSManagedMachinePools

[AndiDog]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This implements the CAPI MachinePool Machines proposal.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #4184

Special notes for your reviewer:

Revival of #4527. I took @cnmcavoy's great effort and got it fully working. I tested EC2 cluster creation, machine deletion by user, instance creation and termination by ASG scaling, instance termination by user, ...

Checklist:

• squashed commits
• includes documentation
• includes emojis
• adds unit tests
• adds or updates e2e tests

Release note:

Add AWSMachines to back the EC2 instances in AWSMachinePools and AWSManagedMachinePools

[k8s-ci-robot]

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[richardcase]

@AndiDog - it would be good to discuss this in office hours. I'm not sure about including AWSManagedMachinePools in this.

[AndiDog]

@AndiDog - it would be good to discuss this in office hours. I'm not sure about including AWSManagedMachinePools in this.

Agree. I also didn't test EKS yet.

Meanwhile, I'll anyway push a change to separate out the common functions, and rebase onto main.

[sl1pm4t]

Thanks for this @AndiDog - just want to confirm that this has resolved our issues with autoscaler failing to scale down MachinePools! 🚀

[AndiDog]

Office hours decision: we want to put this new behavior behind a feature flag in order to get this feature merged more easily and keep it as experimental for now

[AndiDog]

Office hours decision: we want to put this new behavior behind a feature flag in order to get this feature merged more easily and keep it as experimental for now

Feature gate now implemented – @richardcase maybe you want to have a look if it's acceptable like this.

[k8s-ci-robot]

PR needs rebase.

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