I am new to AWS. Following this article https://aws.amazon.com/blogs/networking-and-content-delivery/application-load-balancer-type-target-group-for-network-load-balancer/

I want to put NLB in FE to be reached from internet and ALB as target group.

What I understand that is the route : NLB->ALB->ECS Fargate instances

When I created NLB in public subnets that have Internet Gateway, I cannot reach NLB and NLB cannot reach ALB even there is security groups defined.

When I created NLB in private subnest as like ALB it can reach ALB, still I cannot reach NLB through internet

When creating NLB in the mapping section this is the description

Mappings
Select one or more Availability Zones and corresponding subnets. Enabling multiple Availability Zones increases the fault tolerance of your applications. The load balancer routes traffic to targets in the selected Availability Zones only. Availability Zones that are not supported by the load balancer or the VPC are not available for selection.

“The load balancer routes traffic to targets in the selected Availability Zones only”

explanation seems like it is not subnet of NLB it should be subnet of targets. There is something missing. I am really stuck for days with those concepts.

I tried to create NLB in public subnet and I tried to create NLB in private subnet. None of it makes it publicly accessible but creating it in private subnet same as ALB makes health checks healthy.