The health check on our ECS cluster is failing on a service that is using an ELB Network Load Balancer on TCP port (gRPC running in docker alpine). The service is using dynamic port mapping for containers.
I tried to telnet on the TCP port from a bastion machine and it did work. The same setup has worked with using ALB on HTTP port with dynamic port mapping after also adding the ALB security group to be allowed to send traffic to nodes in the VPC
The nodes running in the private subnets of the VPC and the balancer is an internal ELB
Any idea what might be wrong?