Like at EC2, each server is given a public DNS address, when looked up from outside the private network it resolves to the public IP, but when looked up from another server within the private network the private IP is resolved.
I'm extremely surprised this isn't done. This is a major feature that would greatly reduce congestion on their external interfaces.
For every address added to DNS, a checkbox should be listed that says "enable split horizon". When checked, if a droplet resolves another droplet and they both have private networking, the private address will be returned. Making this automatic and easy for your customers will increase bandwidth utilization of the private interfaces.
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