CloudFront & Origin — SAA-C03 Practice Question
A representative AWS Solutions Architect Associate (SAA-C03) exam question on CloudFront & Origin. Work through it below, then read why each option is right or wrong.
Short answer
The correct answer is A. Enable Origin Shield as an additional caching layer between CloudFront edge locations and the S3 origin.
Origin Shield adds a centralized caching layer between regional edge caches and the origin. With millions of titles, individual edge locations may not have a specific video cached, but Origin Shield consolidates cache misses across all edge locations into a single point. If any edge location previously requested the video, Origin Shield likely has it cached. This dramatically reduces cache misses at the origin and improves first-segment delivery for a long-tail catalog.
The Question
A video streaming company serves on-demand content through Amazon CloudFront. The content is stored in S3. Users report buffering issues during peak hours, particularly for the initial seconds of video playback. Analysis shows that the first segment of each video has a cache miss rate of 40% at edge locations because of the large video catalog (millions of titles). The company wants to reduce the initial buffering for all videos. Which solution reduces the cache miss rate for initial video segments?
Why A is correct
Origin Shield adds a centralized caching layer between regional edge caches and the origin. With millions of titles, individual edge locations may not have a specific video cached, but Origin Shield consolidates cache misses across all edge locations into a single point. If any edge location previously requested the video, Origin Shield likely has it cached. This dramatically reduces cache misses at the origin and improves first-segment delivery for a long-tail catalog.
Why the other options are wrong
Increasing TTL does not help with cache misses — if the video was never cached at a specific edge location (because of the long-tail distribution), a longer TTL does not matter. The issue is that millions of titles spread across hundreds of edge locations means most titles are not cached at most locations.
Lambda@Edge prefetching adds complexity and cost. Lambda@Edge has a 30-second timeout for origin-facing events and limited memory. Prefetching millions of videos at edge locations is not feasible, and the problem is edge cache capacity, not timing.
Multiple origin groups with failover improve availability (if one origin is unavailable), not caching performance. S3 replicas in different Regions do not reduce cache miss rates — they just provide origin redundancy.
Key idea: CloudFront & Origin
Why A is correct: Origin Shield adds a centralized caching layer between regional edge caches and the origin. With millions of titles, individual edge locations may not have a specific video cached, but Origin Shield consolidates cache misses across all edge locations into a single point. If any edge location previously requested the video, Origin Shield likely has it cached. This dramatically reduces cache misses at the origin and improves first-segment delivery for a long-tail catalog. Why B is wrong: Increasing TTL does not help with cache misses — if the video was never cached at a specific edge location (because of the long-tail distribution), a longer TTL does not matter. The issue is that millions of titles spread across hundreds of edge locations means most titles are not cached at most locations. Why C is wrong: Lambda@Edge prefetching adds complexity and cost. Lambda@Edge has a 30-second timeout for origin-facing events and limited memory. Prefetching millions of videos at edge locations is not feasible, and the problem is edge cache capacity, not timing. Why D is wrong: Multiple origin groups with failover improve availability (if one origin is unavailable), not caching performance. S3 replicas in different Regions do not reduce cache miss rates — they just provide origin redundancy. On the SAA-C03 exam, questions in the "Design High-Performing Architectures" domain test whether you can map a scenario's constraints to the right choice. Read the requirement carefully, eliminate options that violate any single constraint, and pick the one that satisfies all of them with the least operational overhead.
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