Caching And Content Delivery Optimization — AWS SysOps Administrator (SOA-C03)
High Cache Miss Rate Is a Configuration Problem, Not Capacity
A scenario describes high origin load despite CloudFront being deployed in front of the application. The instinct is to scale origin instances. The exam points to cache behavior configuration: TTLs set too low, or cache keys that include user-specific headers, prevent effective caching even when content is identical across users. The fix is a CloudFront cache policy change, not horizontal scaling. Treating a caching misconfiguration as a capacity problem is a category error the exam rewards you for avoiding.
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
Whether to configure two path-specific cache behaviors—CachingOptimized mapped to the S3 origin for /assets/* and CachingDisabled mapped to the ALB origin for /api/*—versus a single default cache behavior with a long TTL that satisfies static caching but over-provisions caching onto the dynamic path, risking stale personalised or transactional responses.
Domain Coverage
Difficulty Breakdown