Настройки бэкенда:

server {
    listen 80;
    server_name *.example.ru;

    root /var/www/example.ru/public_html;
    index index.php;

    access_log off;
    error_log /var/www/example.ru/log/error.log crit;

    client_max_body_size 32m;

    location / {
        try_files $uri $uri/ /index.php?$query_string;
    }

    location ~ \.php$ {

        fastcgi_buffers 4 256k;
        fastcgi_busy_buffers_size 256k;
        fastcgi_temp_file_write_size 256k;

        try_files $uri =404;
        fastcgi_pass unix:/var/run/phpfpm-example.sock;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;

        include fastcgi_params;
    }
}