I am relatively new to AWS. I've been able to:

• Setup edge-optimized API Gateway endpoints (w/a custom domain ... install an SSL cert, etc.)
• Route requests from API Gateway to a server running on an EC2 instance via HTTP proxy

For learning, I'd like to put a Network Load Balancer (NLB) between API Gateway and the EC2 instance. After that, I want to experiment with Auto-Scaling Groups (in order to see how EC2 instances can be scaled out/in).

BUT I'm stuck on the NLB. After adding it in, requests made to API Gateway endpoints simply return internal server error.

Question

Should I be using an internal or internet-facing NLB to route the requests from API Gateway to the EC2 instances?

• When I opt to use an internal NLB, I get a warning message You are creating an internal Load Balancer, but there is an Internet Gateway attached to these subnets ... and then I run into the internal server error problem.
• When I setup an internet-facing NLB, API Gateway warns me something to the effect of, "Your NLB is already public-facing, so the use of a VPC Link might be unnecessary".

Can someone shed some light on what I should be doing?