NGINX proxy on ECS - Address already in use. How to do a dynamic port assignment to ALB and Security groups?

Hello,

I am facing an issue when running NGINX as a proxy service with two tasks - they seem to be fighting over one port (nginx: [emerg] bind() to 0.0.0.0:8999 failed (98: Address in use)), which can be easily resolved by only having only one replica. Now, I am curious how I would approach this problem if I wanted more replicas which are being load balanced by the ALB. Setting a dynamic port 0 means that there is a big chance that the Security Group will deny access to it, as only a few ranges are allowed.