SearchVarnish Enterprise
is_healthy is an Enterprise only boolean varnishstat counter that directly gives you the health of backends, without having to deal directly with probes.
The is_healthy counter will be either a 1 if a backend is currently healthy, or a 0 if it is unhealthy. Backend health status is determined by any and all active health probes defined in your VCL. However, backend health can be overridden through the Varnish CLI, at which point the counter will not reflect the probe status anymore. It can be restored by setting backend health to auto.
When inspecting the counter with varnishstat in interactive mode, the value will appear as either true or false.