WebSocketと同様の設定でLong Pollingが利用可能なようです。
server { listen 80; server_name example.com; root /path/to/docment_root; location / { try_files $uri @upstream; } location @upstream { proxy_pass http://127.0.0.1:8080; proxy_http_version 1.1; proxy_set_header Upgrade $http_upgrade; proxy_set_header Connection "upgrade"; } }