How to simulate upstream with Nginx for dynamic subdomains - nginx

Question

I would proxy a request like the upstream solution.
server_name ~^(?<subdomain>.+)\.example\.com$;
root /dev/null;
location / {
error_page 502 #nextserver;
resolver 127.0.0.1:53 valid=300s;
proxy_pass "https://$subdomain";
}
location #nextserver {
error_page 502 #error;
resolver 127.0.0.1:53 valid=300s;
proxy_pass "https://$subdomain-blahblah";
}
location #error {
return 502 'Service is not available';
}
As you can see I would check https://$subdomain and if it doesn't exist or it down then checks https://$subdomain-blahblah.
it works fine but the problem happen when the second server is down, then Nginx doesn't provide Service is not available message.
So the scenario is like
check Server A -> down
check Server B -> down
Return custom error
I couldn't use upstream because the name of servers is dynamic.

Answer 1

I would suggest you to solve this problem differently. Check out this sample. It shows how you can approach the problem:
http{
listen 80;
root /path/to/static/files;
upstream_server subdomain1{
server 192.168.1.100:8000;
server 192.168.1.101:8000;
}
upstream_server subdomain2{
server 192.168.1.102:8000;
server 192.168.1.103:8000;
}
location / {
server_name subdomain1.example.com;
proxy_pass http://subdomain1;
include /etc/nginx/proxy_pass;
}
location / {
server_name subdomain2.example.com;
proxy_pass http://subdomain2;
include /etc/nginx/proxy_pass;
}
}