What is an AWS Security Group?

An AWS Security Group acts as a virtual firewall that controls both inbound and outbound traffic to Amazon Elastic Compute Cloud (EC2) instances and other resources within a Virtual Private Cloud (VPC). Security Groups allow users to define rules that permit or deny traffic based on criteria such as IP addresses, protocols, and port numbers. This capability is essential for managing access to resources and ensuring that only authorized traffic can reach those resources, enhancing security within your AWS environment.

The underlying concept of Security Groups is to provide a layer of security at the instance level. When you launch an instance, you can associate one or more Security Groups with it, dictating how that instance interacts with other instances and the outside world. By default, Security Groups deny all inbound traffic and allow all outbound traffic, but you can make specific adjustments to open up particular ports or allow traffic from specific IP ranges as needed.

Understanding this function is vital for effective network security in AWS, as it directly impacts how resources communicate with each other and with external networks.