Hetzner With Load Balancer leads to 503 Service Unavailable

[Crease29]

Hey Community,

I tried following the Load Balancing on Hetzner guide, but I'm stuck.

My goal is to serve all subdomains of my domain through one Load Balancer. Therefore I have to use a proxy within Coolify (I assume).

Result when trying to access https://<MYDOMAIN>.com in my browser:

Here's my setup:

1. 2 servers on Hetzner, which are in the same private network
2. A firewall which has opened port 22, 80 (not sure if that port 80 rule is even needed)
3. A load balancer in the same region, same network and both servers assigned. SSL certificate is set up.
   Service settings:
   
4. IPv4 and IPv6 addresses of the load balancer assigned to the @ and * A records in the DNS zone of my domain.

Here's my Coolify setup:

1. The instance domain is set to the subdomain http://coolify.<MYDOMAIN>.com (left out https because from what I understand the load balancer communicates over port 80)
2. Both servers added (localhost and the other one)
3. Both have the Caddy proxy running, but I also tested with "None" proxy.
4. One application with the strm/helloworld-http docker image running, which exposes port 80. I have deployed this image to both my servers. The domain name for this is set to http://<MYDOMAIN>.com.

What I don't yet understand is how can coolify correctly route the traffic to the correct container without any proxy running? Because that's what the Load Balancing on Hetzner guide suggests.

If you need any further information to narrow down where exactly the problem might be, please feel free to ask.

Thank you very much in advance!