CDN Content Distribution & Caching 3 — Questions and Answers
Question 1: Which CDN feature allows different versions of the same URL to be cached based on the user's geographic location?
- Geo-blocking
- Vary-based caching with geographic keys (Correct answer)
- Cache key normalization
- Edge-side includes (ESI)
Correct answer: Vary-based caching with geographic keys
Adding geographic identifiers to the cache key enables distinct cached responses per region for the same URL.
Question 2: What is the primary risk of setting excessively long TTLs (e.g., 1 year) for HTML pages on a CDN?
- Increased origin server load
- Stale content being served after site updates (Correct answer)
- Higher storage costs at edge nodes
- Slower TTFB for first-time visitors
Correct answer: Stale content being served after site updates
Long TTLs mean updated HTML may not reach users until caches expire, requiring manual purges for timely updates.
Question 3: A CDN uses 'request coalescing' (also called request collapsing). What problem does this solve?
- Reduces the number of TLS handshakes per session
- Prevents multiple simultaneous cache misses from all hitting origin for the same resource (Correct answer)
- Merges small HTTP/2 frames for efficiency
- Combines multiple CSS files into a single request
Correct answer: Prevents multiple simultaneous cache misses from all hitting origin for the same resource
Request coalescing queues duplicate in-flight requests at the edge so only one request goes to origin, preventing thundering herd.
Question 4: Which metric specifically measures the percentage of requests served from CDN cache without hitting origin?
- Cache hit ratio (CHR) (Correct answer)
- Time to First Byte (TTFB)
- Origin offload percentage
- Edge availability SLA
Correct answer: Cache hit ratio (CHR)
Cache hit ratio is the fraction of total requests served from cache, directly measuring CDN caching effectiveness.
Question 5: Edge Side Includes (ESI) are primarily used to:
- Compress edge-to-origin connections
- Assemble web pages from individually cacheable fragments at the edge (Correct answer)
- Encrypt content between edge nodes
- Balance load across multiple origin servers
Correct answer: Assemble web pages from individually cacheable fragments at the edge
ESI allows edge servers to stitch together page fragments with different cache lifetimes, enabling partial page caching.
Question 6: A CDN operator wants to ensure API responses with sensitive user data are never cached. Which Cache-Control combination is most appropriate?
- max-age=0, must-revalidate
- no-cache, no-store, private (Correct answer)
- no-cache, s-maxage=0
- private, max-age=60
Correct answer: no-cache, no-store, private
'no-cache, no-store, private' prevents both storage and serving of sensitive responses at any cache layer.
Question 7: What is 'origin shield' (also called 'shield PoP' or 'mid-tier caching') in a CDN architecture?
- A firewall placed in front of the origin server
- A designated intermediary CDN node that aggregates cache misses before they reach origin (Correct answer)
- An SSL certificate pinning mechanism at origin
- A redundant origin server for failover
Correct answer: A designated intermediary CDN node that aggregates cache misses before they reach origin
Origin shield is a single CDN node that acts as a proxy for all edge nodes, dramatically reducing origin traffic on cache misses.
CDN Content Distribution & Caching 3
Which CDN feature allows different versions of the same URL to be cached based on the user's geographic location?