Design a CDN / Edge Caching System
Problem
Design Akamai's core competency: a CDN with edge caching serving content globally with high cache-hit ratios.
Requirements
Functional:
- Cache content at edge PoPs near users
- Validate and refresh on expiry
- Purge/invalidate content
- Origin failover
Non-functional:
- Trillions of requests/day
- Low latency, high hit ratio
- Resilient to origin failures
Discussion points
- Edge PoP + tiered caching
- Cache key and TTL strategy
- Cache invalidation/purge propagation
- Origin shielding and failover
- Handling cache misses and validating headers
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