Multi-CDN Strategy & Failover Flashcards

In a multi-CDN deployment, which HTTP header should the origin always include to enable downstream CDN nodes to cache responses correctly and consistently?

Answer: Cache-Control with explicit directives (max-age, s-maxage)

Cache-Control headers with explicit s-maxage or max-age directives tell CDN edge nodes precisely how long to cache responses, ensuring consistent behavior across all providers.

A multi-CDN operator notices that failover to CDN-B causes a surge in origin traffic. What is the most likely cause?

Answer: CDN-B's cache is cold because it receives little traffic in normal active-passive operation

In active-passive setups, the standby CDN receives minimal traffic and therefore has an empty or poorly populated cache, causing cache misses and origin surges during failover.

Which approach allows a multi-CDN control plane to make routing decisions based on both performance AND cost simultaneously?

Answer: Use a weighted scoring function that combines RUM latency data with CDN cost-per-GB pricing

A weighted scoring function allows operators to define the trade-off between performance and cost, enabling nuanced traffic distribution that optimizes both dimensions.

What is the role of BGP anycast in multi-CDN architecture compared to DNS-based steering?

Answer: BGP anycast allows network-layer routing to the nearest PoP within a single CDN; DNS steering directs traffic between CDN providers

BGP anycast operates at the network layer to find the nearest PoP within one provider's network, while DNS-based steering selects which CDN provider serves a given request.

A content publisher updates a video file and triggers a purge across two CDN providers. CDN-A confirms purge success but CDN-B returns a 207 partial-success response. What is the safest next step?

Answer: Re-issue the purge request to CDN-B for the failed objects and verify completion before serving traffic

Re-issuing the purge for failed objects and verifying completion ensures no stale content is served from CDN-B without disrupting normal service.

Which protocol or standard enables a multi-CDN control plane to programmatically configure caching rules across different CDN providers through a unified interface?

Answer: CDNI (CDN Interconnect) as defined by IETF RFC 8804

The IETF CDNI framework provides standardized interfaces for CDN interconnection and inter-provider content delivery coordination.

A retail site uses CDN-A for static assets and CDN-B for API acceleration. During Black Friday, CDN-B's dynamic caching is overwhelmed. Which multi-CDN design flaw does this expose?

Answer: The architecture lacks redundancy for the API acceleration tier; both CDNs should handle all traffic types

Assigning CDN responsibilities by content type creates single points of failure for each tier; both CDNs should be capable of serving all content types for true redundancy.