What is happening?

The server is unable to get response from the website's server-side script.

What I can do?

If your are a website visitor:
Please try again after few minutes.

If you are the developer or website owner:
You can look at your Varnish error logs on cPanel > Fastest Cache > Error logs. Common reasons are following:

• Entry Processes limit is reached on your hosting subscription.
• HTTP request is terminated by a ModSecurity rule.
• Varnish timeout is reached (100s first byte or 100s between bytes). If you are using PHP, profile with xDebug to see the exact execution time of each part of your script.
• Any ongoing maintenance prevent Varnish to reach Apache.