Varnish Cache Hitpass Indicates Backend Overload Risk
warningHigh 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.
Monitor varnish_cache_hitpass rate increase alongside backend connection metrics. If hitpass rate rises while backend response times increase or Apache MaxRequestWorkers approaches capacity, cache bypass is overwhelming the origin.
Review Varnish VCL configuration to identify why requests are passing through cache. Check for unnecessary 'pass' decisions in vcl_recv or vcl_backend_response. Consider adjusting cache TTLs, implementing grace mode for stale content, or optimizing Apache's ProxyTimeout and connection pooling to handle cache misses more efficiently.