I have a public API gateway set up, I want to forward the requests from API Gateway to a private ALB in the VPC. On AWS Console, for API Gateway VPC link setup I could only select an NLB in the VPC.
Currently AWS only supports connecting to NLB for VPC link integrations. They have a feature request in place to enable support for ALB as well. For now, you can do -
Public API --> VPC Link --> NLB --> ALB
In the target groups of the NLB, add the private IPs of the ALB. This way you can reap benefits of the NLB (TCP layer) and ALB (HTTPS).