Security groups are the AWS service or feature that can be used to apply security rules to specific Amazon EC2 instances. Security groups are virtual firewalls that control the inbound and outbound traffic for one or more instances. Customers can create security groups and add rules that reflect the role of the instance that is associated with the security group. For example, a web server instance needs security group rules that allow inbound HTTP and HTTPS access, while a database instance needs rules that allow access for the type of database12. Security groups are stateful, meaning that the responses to allowed inbound traffic are alsoallowed, regardless of the outbound rules1. Customers can assign multiple security groups to an instance, and the rules from each security group are effectively aggregated to create one set of rules1.

Network ACLs are another AWS service or feature that can be used to control the traffic for a subnet. Network ACLs are stateless, meaning that they do not track the traffic that they allow. Therefore, customers must add rules for both inbound and outbound traffic3. Network ACLs are applied at the subnet level, not at the instance level.

AWS Trusted Advisor is an AWS service that provides best practice recommendations for security, performance, cost optimization, and fault tolerance. AWS Trusted Advisor does not apply security rules to specific Amazon EC2 instances, but it can help customers identify security gaps and improve their security posture4.

AWS WAF is an AWS service that helps protect web applications from common web exploits, such as SQL injection, cross-site scripting, and bot attacks. AWS WAF does not apply security rules to specific Amazon EC2 instances, but it can be integrated with other AWS services, such as Amazon CloudFront, Amazon API Gateway, and Application Load Balancer.