AWS Network ACLs
AWS Network ACLs (Network Access Control Lists) are a stateless firewall feature within Amazon Virtual Private Cloud (VPC) that controls inbound and outbound traffic at the subnet level. They operate as an optional layer of security that evaluates traffic based on rules defined by administrators, allowing or denying packets based on IP addresses, ports, and protocols. Unlike security groups, Network ACLs are stateless, meaning return traffic must be explicitly allowed by separate rules.
Developers should learn and use AWS Network ACLs when designing secure VPC architectures that require granular subnet-level traffic control, such as isolating public and private subnets or implementing compliance requirements like PCI-DSS. They are essential for scenarios where you need to block specific IP ranges, restrict traffic between subnets, or add an extra layer of defense beyond security groups, especially in multi-tier applications or regulated environments.