CDN Content Distribution & Caching 2 — Questions and Answers
Question 1: Which cache eviction policy removes the item that has not been accessed for the longest period of time?
- First In, First Out (FIFO)
- Least Recently Used (LRU) (Correct answer)
- Least Frequently Used (LFU)
- Random Replacement (RR)
Correct answer: Least Recently Used (LRU)
LRU evicts the item whose last access time is the oldest, making it ideal for workloads with temporal locality.
Question 2: A CDN edge node receives a request for a resource with 'Cache-Control: no-store'. What must the CDN do?
- Cache the resource but never serve it from cache
- Cache the resource for 1 second only
- Not store any part of the request or response (Correct answer)
- Store the resource in memory only, not on disk
Correct answer: Not store any part of the request or response
'no-store' is the strictest directive, instructing the CDN to never persist any part of the transaction.
Question 3: What is 'cache warming' in the context of CDN operations?
- Increasing edge server temperature thresholds
- Pre-populating edge caches with content before user requests arrive (Correct answer)
- Gradually increasing TTL values over time
- Enabling keep-alive connections on cache servers
Correct answer: Pre-populating edge caches with content before user requests arrive
Cache warming proactively pushes content to edge nodes to avoid cold-start latency spikes when traffic begins.
Question 4: Which HTTP header does a CDN use to indicate that a cached response is stale but still being served while a background revalidation occurs?
- Age: stale
- Warning: 110 (Correct answer)
- X-Cache-Status: STALE
- Cache-Control: stale-while-revalidate
Correct answer: Warning: 110
HTTP Warning code 110 ('Response is Stale') signals that the CDN is serving a stale cached response.
Question 5: A media company serves video segments of varying popularity. Which caching strategy best handles a long-tail content distribution?
- Cache only the top 10% most popular segments
- Use tiered caching with a large regional cache behind edge nodes (Correct answer)
- Set uniform TTLs of 24 hours for all segments
- Disable caching for segments with fewer than 100 views
Correct answer: Use tiered caching with a large regional cache behind edge nodes
Tiered caching allows long-tail content to be fetched once to a regional parent cache and then served to multiple edge nodes.
Question 6: What does the 's-maxage' directive in a Cache-Control header specifically control?
- Maximum age for browser caches only
- Maximum age for shared caches such as CDN edge nodes (Correct answer)
- The staleness window for service workers
- How long stale content can be served while revalidating
Correct answer: Maximum age for shared caches such as CDN edge nodes
's-maxage' overrides 'max-age' specifically for shared/proxy caches, allowing different TTLs for CDN vs. browser.
Question 7: When a CDN edge node returns an HTTP 304 Not Modified response to a browser, what has occurred?
- The CDN served the full content from its cache
- The CDN confirmed the browser's cached copy is still valid (Correct answer)
- The CDN fetched fresh content from origin
- The CDN purged the requested resource
Correct answer: The CDN confirmed the browser's cached copy is still valid
A 304 tells the browser its cached version matches the current version, so no body is transmitted, saving bandwidth.
CDN Content Distribution & Caching 2
Which cache eviction policy removes the item that has not been accessed for the longest period of time?