There is only one network interface in EC2 instance, and in the CloudWatch metric, I can only see "Max Network In" and "Max Network Out".
As you know external traffic is billed (actually only outbound), is it possible to check my out bound traffic so I can easily compute the cost?
You can install iftop in your ubuntu server (sudo apt-get install iftop) then run the command in terminal "iftop"
it will display you all in/out traffic realtime in terminal.