VPC NetworkOUT metric on Cloudwatch

There is no traffic metrics for internet gateway. You could use Cloudwatch metric math to sum all out-going traffic of your NAT gateways. This would be the same as traffic to internet IF you don't have anything but NAT GWs in your public subnets. It wouldn't include traffic out from other instances, load balancers etc from public subnets. If you absolutely must know traffic out to internet in near real-time you could enable VPC Flow Logs and then parse and sum lines where target is not within your VPC or any other internet networks. Without knowing the use-case this feels bit a bit overkill.

• https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/using-metric-math.html
• https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Scenario2.html
• https://docs.aws.amazon.com/vpc/latest/userguide/flow-logs.html

Ps. Cloudwatch metric math would allow you follow NAT utilisation and alert if your NAT gateway(s) are becoming a bottle-neck. Here is a Cloudnonaut's blog about monitoring NAT performance https://cloudonaut.io/nat-gateway-monitoring-with-cloudwatch-metrics-and-alarms/