1server {
2...
3    location / {
4        proxy_pass http://localhost:3000;
5        proxy_http_version 1.1;
6        proxy_set_header Upgrade $http_upgrade;
7        proxy_set_header Connection 'upgrade';
8        proxy_set_header Host $host;
9        proxy_cache_bypass $http_upgrade;
10    }
11...
12}