how to know data transfer volume from ec2 to s3

Hi,

You want to use the VPC Flow Logs to achieve the level of granularity that you need in your use case.

See https://aws.amazon.com/blogs/aws/vpc-flow-logs-log-and-view-network-traffic-flows/

Reference documentation is here : https://docs.aws.amazon.com/vpc/latest/userguide/flow-logs.html

Best

Didier