I am running a proxy lambda behind an API Gateway which forwards my requests to my Application Load Balancer (ALB), but the requests time out. I am sending them from the lambda console directly. Requests from my company's domain (e.g. my local with Postman) to the ALB's alias DNS entry are successful.
The lambda is running in the same VPC as the ALB, and running in the private subnets and the ALB in the public ones. I have tried putting the ALB in the private subnets, but that did not solve the issue (I made no other configuration changes than the subnets).
I allow inbound connections in the ALB Security Group (SG) for the lambda's SG on 80 and 443, as well as for the VPC in general. The lambda's SG allows all outbound requests. The Network ACL on the public subnets (ALB) allow all inbound traffic, and the ACL on the private subnets (proxy lambda) allow all outbound traffic.
I have tried sending the HTTP requests to both the ALIAS of the ALB's DNS entry, as well as the direct URL, and both time out. I receive errors from sending requests to invalid URLs, and receive 200s from valid public URLs.
My Route 53 logs show that the DNS Resolver receives and forwards the request (which looks identical to other successful requests), but there is no corresponding log for the ALB saying that it was received, and I don't have any rejections in my VPC flow log.
Do you know what might be the issue and how I can correct it?
