I think this goes on this page
https://mms.mongodb.com/help/core/automation-checklist/

(We may need a "VPC" sub header)

If someone is using a VPC they created (rather than one of the default aws VPCs)
1. they should make sure the VPC property "DNS hostname" is set to yes, which guarantees that each instance provisioned in the VPC receives a hostname
2. they should make sure that, for all subnets they create, when they click the "Modify auto-assigned public IP" button in the console, the box "Enable auto-assign Public IP" is checked

Thanks