AWS - Unable to make API calls to EC2 server via Application Load Balancer (ALB)

问题

I am trying to deploy a MERN Stack app to AWS but I am kinda stuck now.

Current Progress:

1. ALB is set up with a valid SSL Certificate issued by AWS.

   ALB URL: https://xyz.alb.com/

   Also, ALB has three listeners:

    a. HTTP [80]
    b. HTTPS [443]
    c. HTTPS [5000] (For accessing ec2 backend server, is this right?)
   

2. EC2 instance public IP: 78.45.43.23 (Say)

   (I can access my server on 78.45.43.23:5000/api/)

3. I have whitelisted, ALB, https://xyz.alb.com in my server CORS (Node) [Important].

Problem Statement:

When making an API call now to https://xyz.alb.com:5000/api/getUser, ideally, it should redirect to 78.45.43.23:5000/api/getUser and get me the response since I have the target instance setup [healthy ec2 instance].

But instead, I get,

Access to fetch at 'https://xyz.alb.com:5000/api/getUser' from origin 'https://xyz.alb.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

In short, I am not sure if I am being able to hit my server at PORT 5000 or not, by using the ALB URL!

I would be more than happy to provide any code/screenshot further needed to support my question.

Thanks in advance!

来源：https://stackoverflow.com/questions/63317832/aws-unable-to-make-api-calls-to-ec2-server-via-application-load-balancer-alb