ESI Processing Errors Cascade to Backend Overload
warningElevated varnish_esi_errors or varnish_esi_warnings indicate Edge Side Includes processing failures, which can trigger multiple backend requests per page load and overwhelm Apache with cascading sub-requests.
Track varnish_esi_errors and varnish_esi_warnings rates, especially when request latency increases and varnish_backend_fail spikes. Multiple ESI fragments failing to render can cause exponential backend request amplification.
Review ESI fragment timeout configurations and ensure Apache can handle the request fan-out from ESI includes. Implement ESI fragment caching with appropriate TTLs to reduce backend hits. Consider setting grace periods for ESI fragments so stale content can be served during backend issues. Monitor Apache's MaxRequestWorkers to ensure it can handle ESI sub-request bursts.