Learn how to troubleshoot and fix application connection drops caused by NAT gateway idle timeouts on AWS by monitoring CloudWatch metrics and configuring TCP keepalive.
Table of Contents
Question
A company runs an application on Amazon EC2 instances. A network engineer implements a NAT gateway in the application’s VPC to replace self-managed NAT instances. After the network engineer shifts traffic from the self-managed NAT instances to the NAT gateway, users begin to report issues.
During troubleshooting, the network engineer discovers that the connection to the application is closing after approximately 6 minutes of inactivity.
What should the network engineer do to resolve this issue?
A. Check for increases in the IdleTimeoutCount Amazon CloudWatch metric for the NAT gateway. Configure TCP keepalive on the application EC2 instances.
B. Check for increases in the ErrorPortAllocation Amazon CloudWatch metric for the NAT gateway. Configure an HTTP timeout value on the application EC2 instances.
C. Check for increases in the PacketsDropCount Amazon CloudWatch metric for the NAT gateway. Configure an HTTPS timeout value on the application EC2 instances.
D. Check for decreases in the ActiveConnectionCount Amazon CloudWatch metric for the NAT gateway. Configure UDP keepalive on the application EC2 instances.
Answer
A. Check for increases in the IdleTimeoutCount Amazon CloudWatch metric for the NAT gateway. Configure TCP keepalive on the application EC2 instances.
Explanation
The solution that will resolve this issue is A:
- Check for increases in the IdleTimeoutCount Amazon CloudWatch metric for the NAT gateway
- Configure TCP keepalive on the application EC2 instances
This will:
- Monitor the IdleTimeoutCount metric, which indicates NAT gateway idle timeouts
- Configuring TCP keepalive will generate periodic traffic to prevent idle timeouts
The other options will not address the root cause:
B – ErrorPortAllocation is irrelevant here
C – PacketsDropCount is not the metric to check
D – ActiveConnectionCount decreasing is expected behavior
By checking the appropriate IdleTimeoutCount metric and configuring TCP keepalive traffic, the network engineer can diagnose and prevent the NAT gateway idle timeout issue closing connections.
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