AWS Certified Advanced Networking Specialty Practice Exam

If users report problems accessing a public EC2 instance, which AWS feature could help diagnose the issue?

1. VPC Flow Logs

2. DNS health checks

3. Instance Status Checks

4. CloudWatch Alarms

The correct answer is: VPC Flow Logs

VPC Flow Logs are a powerful tool for diagnosing network connectivity issues with a public EC2 instance. They allow you to log and monitor the flow of traffic to and from network interfaces in your VPC. When users report problems accessing an EC2 instance, examining VPC Flow Logs can reveal important details such as source and destination IP addresses, ports, and the allowed or denied status of the traffic. By analyzing these logs, you can determine whether the traffic actually reaches the instance, if any security group rules or network ACLs are blocking the requests, and identify any abnormal patterns or spikes in traffic that could indicate potential issues. This capability is crucial for troubleshooting various connectivity and performance problems. Other options, while useful in certain contexts, do not directly aid in diagnosing access issues as effectively as VPC Flow Logs. For example, DNS health checks focus on the availability of DNS records and responses, not the traffic flow to the instance. Instance Status Checks monitor the operational status of the EC2 instance itself but do not provide insight into network traffic. CloudWatch Alarms can track metrics and notify on certain thresholds but do not provide specific data on network access problems. Thus, VPC Flow Logs stand out as the most relevant feature for diagnosing access issues with a