Software Design

CDN Edge Caching and ETag Validation Flow

UML Sequence Diagrams · made in Skemio

UML sequence diagram showing a client request hitting a CDN edge, revalidating stale cache with origin via ETag, receiving 304, and serving the client.
UML sequence diagram showing a client request hitting a CDN edge, revalidating stale cache with origin via ETag, receiving 304, and serving the client.
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What it shows

  • Edge POPs serve cached responses instantly without querying the origin.
  • Conditional headers (If-None-Match) revalidate stale content efficiently.
  • 304 Not Modified responses save database compute and origin bandwidth.

The takeaway

Combine Cache-Control TTLs with ETag validation to offload over 90% of requests away from origin servers.

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