If the instances are still running, you can do this using the free basic monitoring that Amazon provides through CloudWatch .
For Amazon EC2 instances, Amazon CloudWatch Basic Monitoring also collects report metrics for CPU usage, data transfer and disk usage activity from each Amazon EC2 instance with a five-minute frequency.
To access the monitor data for an EC2 instance, select it in the AWS Management Console and click on the Monitoring tab in the bottom panel, you can click any of the diagrams (for example, Max Network In) to get a larger version, with some drop-down lists for managing the time window.
Please note that data is only stored for two weeks.
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