NLB Health check failing with network firewall

Hi,

Please look at my solution it will be helpful for you.

Health Check Configuration: the NLB health check configuration matches the protocol and port that your application is listening on. If your application is using TCP, ensure that the health check protocol is set to TCP and the port matches the port your application is listening on.

Firewall Configuration: While the firewall rule may allow any TCP traffic, there could still be some specific configurations or limitations within the firewall that affect the NLB health checks. Check for any rules or settings that might interfere with the NLB health checks, such as deep packet inspection or application layer filtering.

Firewall Logging: Enable logging on the firewall to monitor traffic passing through it. Check the logs for any indications of why the health checks might be failing. Look for any denied or rejected connections that might provide insights into the issue.

NLB Target Configuration: Ensure that the NLB target group is correctly configured to route traffic to the appropriate instances and that the instances are healthy. Check the target group settings, instance health status, and make sure that the instances are properly registered with the target group.

Security Groups and Network ACLs: Verify that the security groups and network ACLs associated with your NLB, instances, and firewall allow traffic to flow between them without any restrictions. Ensure that the necessary ports and protocols are open for communication.

Adding links to support previous answer for troubleshooting https://docs.aws.amazon.com/elasticloadbalancing/latest/network/load-balancer-troubleshooting.html

https://docs.aws.amazon.com/elasticloadbalancing/latest/network/target-group-health-checks.html