NACL and Security Groups

Network access control lists (NACLs) and security groups are types of firewalls that control the network traffic. Security groups are stateful firewalls that analyze everything in the data packets of the incoming traffic and maintain the state. We only need to configure rules for the incoming traffic, and the stateful firewall automatically configures the outgoing rules accordingly. The NACLs are stateless firewalls that check the source, destination, and other parameters/rules to allow or reject the traffic.

Security groups 

In the AWS environment, a security group is a VPC-based resource that works at the EC2 instance level. It validates the incoming traffic and allows only connection requests passed by the inbound rules. We specify a security group to secure our EC2 instance; if no security group is selected, EC2 uses the default security group of the VPC. The default security group has no inbound rules and allows all outbound traffic.