Caching And Content Delivery Optimization — AWS Solutions Architect Pro (SAP-C02)
A Global Catalog Under Heavy Read Load Needs Both Cache Layers
A global e-commerce platform stores product images in S3 and catalog data in Aurora. Peak traffic sends tens of thousands of reads per second against the same top-selling products while users in multiple continents fetch images. CloudFront eliminates origin bandwidth costs for images by serving them from edge locations closest to each user. ElastiCache in front of Aurora serves hot catalog records from memory, bypassing the database engine for every cached hit. The two layers solve different bottlenecks: CloudFront reduces geographic round-trip time for static assets; ElastiCache reduces database load for a small, frequently queried working set. Scenarios describing both symptoms require both layers in the correct positions.
What This Pattern Tests
The exam describes a performance requirement and tests caching layer selection. CloudFront (CDN) caches static content and API responses at edge locations — reduces origin load and latency for geographically distributed users. ElastiCache Redis caches application data (session state, leaderboards, query results) with sub-millisecond reads. DAX sits in front of DynamoDB as a transparent read-through/write-through cache. The trap is using CloudFront to cache highly dynamic, personalized content (low cache hit ratio) or ElastiCache for content that changes every second (cache invalidation overhead exceeds cache benefit).
Decision Axis
Content type and access pattern determine caching layer: static content = CDN, repeated queries = application cache, DynamoDB hot keys = DAX.
Associated Traps
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Decision Rules
Choose the caching tier—purpose-built database-integrated accelerator (DAX) paired with edge caching (CloudFront) versus a general-purpose in-memory cluster (ElastiCache) inserted between the application and DynamoDB—that satisfies the latency SLA without shifting cache invalidation complexity onto the application team.
Domain Coverage
Difficulty Breakdown