New Feature: VPC Flow Log, now available in all regions.
Virtual Private Cloud Flow Logs are now available for all Flexible Engine regions. A VPC flow log records information about the traffic going to and from a VPC. VPC flow logs help you monitor network traffic, analyze network attacks, and determine whether security group and network ACL rules require modification.
This feature is accessed through the Virtual Private Cloud interface on the Flexible Engine Console. You will also need to implement logs through the Log Tank Service.
The VPC flow log feature itself is free of charge, but you may be charged for other resources used such as Log Tank Service or Object Storage Service.
More information on VPC Flow Log is available here.