What is the primary function of security groups in AWS?

The primary function of security groups in AWS is to manage the traffic allowed to reach and leave AWS resources. Security groups act as virtual firewalls that control inbound and outbound traffic to instances in a Virtual Private Cloud (VPC). When you launch an instance, you can associate it with one or more security groups that specify rules for the types of traffic that can access the instance and the types of traffic that the instance can send out.

These rules can include specifying allowed IP addresses, protocols (like TCP or UDP), and ports. This mechanism ensures that only legitimate traffic as defined by the security group rules is allowed to communicate with the AWS resources, helping to enhance security and manage the connectivity effectively.

The other options, while related to security in different contexts, do not accurately describe the primary role of security groups. They do not handle user authentication, monitor session activities, or provide alerts for unauthorized access attempts—those functions are managed by other AWS services and security tools.