What is the cost-benefit of data transfer between VMs over different regions if we communicate over external IP vs communicating over Internal IP?
As per the document, the cost of egress data transfer over a region is 0.08$/Gib. but not very clear what if we use VPC peering and internal IP to communicate? What will be the data cost then?
If you reach the VM by the public IP, your traffic count against the Internet egress pricing, and depends on the type of tiers chosen (premium or standard)
If you use internal IP and peering, it's VM to VM pricing which is applied
Note: if you use Internet Premium Tier connectivity, you are guaranteed to stay in the Google Network and never go to the internet. It's slightly more expensive than the VM to VM pricing, but the feature/perf will be the same.
That being said, from my experience, the egress cost is ridiculously low compared to all the other cost (Except if you are a Youtube or Netflix competitor).