Technical Glossary & Concepts Reference

A comprehensive dictionary of systems engineering, HTTP caching, and networking terminology used in 17-cdn-caching-proxy.

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Caching & Networking Terms

• RFC 9111: The modern IETF standard specification governing HTTP Caching semantics, replacing RFC 7234.
• Request Coalescing (Single-Flight): An architectural pattern that intercepts multiple concurrent requests for the same uncached resource and collapses them into a single upstream request, protecting origins from thundering herd stampedes.
• Surrogate-Key (Cache-Tag): A response header containing space-separated identifiers that tag cached representations, enabling bulk invalidation of related resources in O(1) time.
• Stale-While-Revalidate (RFC 5861): A Cache-Control directive instructing the proxy to serve an expired cached entry immediately to the client while asynchronously dispatching a background request to fetch fresh content.
• Stale-If-Error (RFC 5861): A Cache-Control directive allowing the proxy to serve an expired cached response if the upstream origin returns a 5xx error or network timeout.
• Canonical Cache Key: A normalized SHA-256 hash derived from the request URL, query parameters (sorted deterministically), and secondary keys from Vary headers.
• Segmented LRU (SLRU): An eviction algorithm that divides cache space into probationary and protected segments, requiring an asset to be accessed at least twice before entering the protected tier.
• Ketama Consistent Hashing: A deterministic hashing algorithm that maps cache keys and server nodes onto a 32-bit ring with virtual nodes, minimizing key migration during node additions or removals.
• Zero-Copy Stream Piping: Transferring raw byte chunks from an ingress socket to an egress socket without deserializing the payload into intermediate application memory.
• Content Negotiation: The HTTP mechanism (Accept-Encoding vs Content-Encoding) allowing clients and proxies to negotiate optimal data formats such as Brotli or Gzip.