Which of the following services can be used to block network traffic to an instance?

Explanations:

Security groups act as virtual firewalls for your instances to control inbound and outbound traffic. They allow or deny traffic based on defined rules, making them effective for blocking network traffic.

Amazon VPC flow logs are used for monitoring and logging network traffic, but they do not block traffic. They provide information about the traffic flow but do not have any control capabilities.

Network ACLs (Access Control Lists) are a set of rules that can be used to allow or deny traffic to and from subnets in a VPC. They provide an additional layer of security and can block network traffic.

Amazon CloudWatch is a monitoring service for AWS resources and applications, providing metrics and logs, but it does not directly block network traffic. It can alert on traffic patterns but cannot enforce rules.

AWS CloudTrail is used for logging and monitoring API calls made in your AWS account. It tracks activity for auditing purposes but does not block network traffic.