Design a Content Delivery Network

Caching & Content DeliveryHarddesign-cdn

Design a global edge network that serves static and cacheable dynamic content from a PoP near the user, while keeping the origin from ever seeing the traffic.

Edge CachingAnycast RoutingOrigin ShieldCache Invalidation

Traffic & Capacity Estimates:

300 PoPs · 100 Tbps peak egress · 95% edge cache hit ratio · <30ms TTFB

Functional Requirements

•Route each client to a nearby healthy PoP and serve cached objects directly from it.
•Fetch and cache on miss, honouring Cache-Control, ETag, and conditional revalidation.
•Support global purge of a URL or cache tag within seconds of a publisher request.
•Serve range requests and large media efficiently without buffering whole objects.

Non-Functional Requirements

•Time to first byte under 30ms for cache hits worldwide.
•A PoP failure must drain to neighbouring PoPs without client-visible errors.
•Origin must be protected from a simultaneous miss stampede across hundreds of PoPs.

Back-of-the-Envelope Math

100 Tbps peak across 300 PoPs = ~330 Gbps per PoP.
At 95% hit ratio the origin sees 5 Tbps — an origin shield tier collapses that to well under 500 Gbps.

Key Architectural Trade-offs

Anycast BGP routing (self-healing, no DNS TTL delay) vs GeoDNS (precise steering, hostage to resolver caching).
Push-based pre-warming for predictable launches vs pull-through caching for the long tail.
Short TTLs with revalidation (fresh, more origin traffic) vs long TTLs with explicit purge (cheap, and now you own an invalidation system).

Click or drag a component onto the canvas, then connect the handles to draw the data flow.

3 nodes · 2 edges

Components · 35

Client & Edge4

Compute & Gateway7

Storage & Caching11

Messaging & Streaming6

Coordination & Ops5

Intelligence2

React Flow