Ensure internetwork traffic privacy in Amazon VPC

Security groups: Security groups allow specific inbound and outbound traffic at the resource level (such as an EC2 instance). When you launch an instance, you can associate it with one or more security groups. Each instance in your VPC could belong to a different set of security groups. If you don't specify a security group when you launch an instance, the instance is automatically associated with the default security group for its VPC. For more information, see Security groups.

Network access control lists (ACL): Network ACLs allow or deny specific inbound and outbound traffic at the subnet level. For more information, see Control subnet traffic with network access control lists.

Flow logs: Flow logs capture information about the IP traffic going to and from network interfaces in your VPC. You can create a flow log for a VPC, subnet, or individual network interface. Flow log data is published to CloudWatch Logs or Amazon S3, and it can help you diagnose overly restrictive or overly permissive security group and network ACL rules. For more information, see Logging IP traffic using VPC Flow Logs.

Traffic mirroring: You can copy network traffic from an elastic network interface of an Amazon EC2 instance. You can then send the traffic to out-of-band security and monitoring appliances. For more information, see the Traffic Mirroring Guide.