Feature request: Cross account ENIs is more complex than just 5 free IPs

[bryantbiggs]

Use case

Currently, its required to have at least 5 free IPs for the control plane cross account ENIs to facilitate an upgrade. However, this isn't the full story since the cross account ENIs will be created in at least 2 different availability zones.

Solution/User Experience

Change EKS001 check to ensure there are at least two subnets in different AZs with at least 4 available IPs each for the control plane cross account ENIs - awsdocs/amazon-eks-user-guide#688

Alternative solutions

Use current guidance of 5 free IPs but this is mis-leading (if you only have 5 free IPs, but all in one subnet, the upgrade would fail)

[bryantbiggs]

Check should be updated to ensure at least 5 free IPs in two subnets in different availability zones used by the control plane