CDN Origin Shield & Pull/Push Zones Flashcards

An operator uses a CDN push zone to distribute a software installer. After uploading a new version, users still receive the old file. What is the most likely cause?

Answer: Edge nodes are serving cached copies of the old file; a purge or cache invalidation is required

Push zone edge nodes cache uploaded files; replacing a file at the origin/storage does not automatically evict cached copies, so a targeted purge is required.

Which CDN feature allows operators to set different cache TTLs at the origin shield layer versus the edge PoP layer?

Answer: Surrogate-Control header or CDN-specific cache directives

Headers like Surrogate-Control (Fastly) or CDN-Cache-Control allow operators to specify longer TTLs at the shield/CDN layer independently of the browser-facing Cache-Control.

What is the trade-off of placing origin shield in a region geographically distant from the origin server?

Answer: Higher cache-hit ratio but increased latency for cache misses that must travel further to origin

A distant shield improves global cache consolidation but adds round-trip latency on cache misses since the shield must fetch from a far origin, increasing time-to-first-byte for uncached requests.

A CDN pull zone is configured with a 1-hour TTL. The origin content is updated. What must the operator do to immediately serve fresh content?

Answer: Issue a cache purge/invalidation for the affected URLs

A cache purge removes the stale object from CDN nodes before TTL expiry, ensuring the next request fetches and caches the updated content from origin.

What HTTP mechanism allows an origin server to validate a cached object at the shield without transferring the full response body?

Answer: Conditional requests using ETag or Last-Modified headers (304 Not Modified)

Conditional GET requests let the shield send an If-None-Match or If-Modified-Since header; the origin returns 304 Not Modified if unchanged, saving bandwidth on revalidation.

Which CDN architecture pattern uses origin shield together with tiered caching across multiple PoP levels?

Answer: Hierarchical (tiered) CDN caching

Tiered caching creates a hierarchy of cache layers (edge PoP → regional shield → origin shield) so misses escalate upward, maximizing cache efficiency before hitting the origin.