Using an IIS server with multiple sites behind an application loadbalancer

Question

I am trying to put some sites on an iis server behind a loadbalancer on aws.

The loadbalancer has ssl certificate from acm.

To have the site reachable on the configured subdomain, I have to bind both the loadbalancer and the subdomain url to the site, but I have more than one site on that server, meaning...I cannot bind the loadbalancer url to more than one site at a time. Why do I have to bind the loadbalancer url to a site before it works, I used to believe binding it to the subdomain url was sufficient?
If I bind only the url of the subdomain to the site, it would be unavailable...please what configuration or steps do I take in cases like this?

Accepted Answer

This was resolved with host headers on alb listener rules pointing to the target group of the instance, once done, it was no longer necessary to bind a site to the alb url

Using an IIS server with multiple sites behind an application loadbalancer

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