amazon web services – Path of connection between two EC2 instances

I have an EC2 instance running in my own VPC. One of my partners also has an EC2 running in their own VPC in AWS. The two instances connect to each other via TCP to exchange data. Connection is made through their DNS address.

I am wondering about two scenarios:

  • The instances are in separate regions
  • The instances are in the same regions

What is the path taken by the TCP connection between the two instances? Does it matter that they both live within AWS? When the instances are in the same region, does the connection ever leave AWS to an external network switch / router?