How to use Amazon ALB port forwarding to run multiple services on a single EC2 instance

Question

I have multiple services running on multiple ports on a single AWS EC2 instances. I've been using two ALBs to run these services, but I'd like to combine them into a single ALB that forwards to the correct service based on the host name. One service is a node app running port 80 and the other is a flask app running on port 5001.

As of now, I have a target group setup as mywebsite for the node app on port 80, and api-service for my flask app on port 5001.

I added those target groups to an ALB, my-alb, and set up forwarding rules so that port 80 and 5001 will forward to port 443. On port 443 I set up forwarding rules so that if the host matches api.* it will forward to the target group api-service otherwise it will default to my-website.

I have also set up my alb as the alias for api.mywebsite.com and www.mywebsite.com on route 53 as well as setting up the certificate. All the health checks are passing for both my target groups.

Here's the issue: www.mywebsite.com works properly. I get forwarded to the https version of the site and everything looks fine. When I try to use api.mywebsite.com it doesn't load and I get a 504 Bad Gateway error.

To summarize, here are the steps I've completed:

1. Setup two target groups for my services on port 80 and 5001
2. Added those two target groups to ALB and set routing rules to redirect to port 443
3. Set forwarding rules for route 443 to forward to the service on port 5001 if the host matches api.* else route to the service on port 80.
4. Set the ALB as the alias for api.mywebsite.com and www.mywebsite.comin route 53.

Any help would be appreciated, thanks!

EDIT: Got it working.

I had configured my security group incorrectly. That is the step I was missing :D. Once I added port 5001 to the security group assigned to my ALB and EC2 it began to work properly.

Thanks!