nginx dynamic proxy_pass with routes (explaining in the source code)

gistfile1.txt

# this config resolves different containers depending on route path, not on ips/domains
# on top of that it uses dynamic resolving, meaning that if some docker containers are not alive 
# nginx will still work. It is achieved by using variables which makes nginx resolve host on runtime and not on start.

# frontend dev env
server {
    # nginx container port
    listen 3001;
    server_name localhost;

    location /auth/back/ {
        # this needed to resolve host by docker dns, othervise 'set $upstream will' not work
        resolver 127.0.0.11 valid=10s;

        # https://stackoverflow.com/questions/71204607/why-does-a-variable-not-work-in-nginx-proxy-pass
        set $upstream <backend-docker-host>;
        rewrite /auth/back/(.*) /$1 break;
        proxy_pass http://$upstream/authorization/$1$is_args$args;

        # this is need to set proper host header for google auth redirect
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwarded-Proto https;
    }

    location /auth/front/ {
        # this needed to resolve host by docker dns, othervise 'set $upstream will' not work
        resolver 127.0.0.11 valid=10s;

        # https://stackoverflow.com/questions/71204607/why-does-a-variable-not-work-in-nginx-proxy-pass
        set $upstream <frontend-docker-host>:3000;
        rewrite /auth/front/(.*) /$1 break;
        proxy_pass http://$upstream/authorization/$1$is_args$args;

        # this is need to set proper host header for google auth redirect
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwarded-Proto https;
    }
}