nginx-reverse-proxy.conf

server {
    server_name example.com;
    
    # optional
    client_max_body_size 100M;
    
    # remove ending /
    # [warn] it may not need for Next.js
    # [warn] it may generate an error when establish socket.io connection
    # rewrite ^/(.*)/$ /$1 permanent;

    location / {
        proxy_pass http://localhost:3000;
    }
}

server {
    server_name www.example.com

    return 301 https://example.com$request_uri;
}

subdomain-to-path.conf

# abc.example.com
server {
  listen 80;
  server_name abc.example.com;
  location / {
    proxy_pass http://127.0.0.1/abc$request_uri;
    proxy_set_header Host example.com;
  }
}