varnish_vbe_boot_default_busy

High rates of hitpass in Varnish suggest requests are bypassing cache and hitting the backend directly, potentially overloading Apache or other upstream servers. This commonly occurs when cache policies are misconfigured or when content is marked as uncacheable.

Elevated varnish_sess_drop signals that Varnish is rejecting connections due to worker thread exhaustion or queue overflow, often caused by slow backend responses keeping workers occupied.

Long KeepAliveTimeout values in Apache combined with high concurrent connections can starve worker threads, causing Varnish to see backends as busy or unresponsive even when Apache has available capacity.