server {
    listen 80;
    server_name _;

    root /usr/share/nginx/html;
    index index.html;

    # SPA: let the router handle unknown paths.
    location / {
        try_files $uri $uri/ /index.html;
    }

    # Socket.IO (websocket + polling) -> backend.
    location /socket.io/ {
        proxy_pass http://${BACKEND_UPSTREAM}/socket.io/;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_read_timeout 60s;
    }

    location /health {
        proxy_pass http://${BACKEND_UPSTREAM}/health;
    }

    # Pageview beacon + admin stats -> backend.
    location /api/ {
        proxy_pass http://${BACKEND_UPSTREAM}/api/;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}
