Check manual page of varnish.backend
HTTP Accelerator Statistics via Varnishstat on Linux: Backend
This check monitors the backend information of Varnish Server provided by 'varnishstat -1'.
The Linux Agent needs to be installed.
No default levels are set. Upper levels can be set for "backend connections busy/too many",
"backend connections failures" and "backend connections unhealthy/not attempted".
One service is created.