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Explain advanced multi-layer caching architecture (CDN, edge, Redis, local) in PHP systems.

Updated May 24, 2026

Short answer

Multi-layer caching improves performance by distributing cached data across CDN, edge nodes, Redis, and local application memory.

Deep explanation

Caching in large PHP systems is layered to reduce latency and database load.

Layers:

  1. CDN cache
  • static assets
  • edge distribution
  1. Edge cache
  • dynamic response caching
  1. Redis cache
  • shared application cache
  1. Local in-memory cache
  • per-request or per-process cache

Cache flow: Request → CDN → Edge → App → Redis → DB

Challenges:

  • cache invalidation complexity
  • stale data propagation
  • consistency across layers

Advanced strategies:

  • cache hierarchies with TTL coordination
  • stale-while-revalidate
  • cache warming strategies
  • request collapsing…

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