CDN Multi-CDN Strategy & Failover 2 — Questions and Answers
Question 1: Which DNS-based technique is most commonly used to distribute traffic across multiple CDN providers in a multi-CDN setup?
- Anycast routing
- GeoDNS with weighted records (Correct answer)
- Round-robin CNAME chaining
- BGP path prepending
Correct answer: GeoDNS with weighted records
GeoDNS with weighted records allows traffic to be directed to different CDN providers based on geography and configured weight percentages.
Question 2: A company uses two CDNs and detects that CDN-A has a 40% cache hit rate while CDN-B has an 85% cache hit rate for the same content. What is the most likely root cause of the disparity?
- CDN-A has fewer PoPs than CDN-B
- CDN-A receives less traffic and its cache warms more slowly
- CDN-B uses a superior eviction algorithm
- CDN-A's TTL settings are configured too low (Correct answer)
Correct answer: CDN-A's TTL settings are configured too low
Excessively low TTL values cause content to expire quickly and force frequent origin fetches, dramatically reducing cache hit rates.
Question 3: In a multi-CDN architecture, what is the primary purpose of a real-user monitoring (RUM) system?
- To test origin server response times synthetically
- To collect performance data from actual end-user sessions and inform CDN routing decisions (Correct answer)
- To benchmark CDN providers against SLA thresholds in a lab environment
- To generate load tests that simulate traffic across all CDN nodes
Correct answer: To collect performance data from actual end-user sessions and inform CDN routing decisions
RUM collects latency, availability, and throughput data from real users to enable intelligent, performance-based CDN traffic steering.
Question 4: Which failover trigger threshold is most appropriate for automated CDN switching in a production multi-CDN environment?
- Switch immediately on any single failed health check
- Switch after 3 consecutive failed health checks within a 60-second window (Correct answer)
- Switch only after manual operator confirmation
- Switch after 50% of users report errors via feedback forms
Correct answer: Switch after 3 consecutive failed health checks within a 60-second window
Requiring multiple consecutive failures within a time window prevents false-positive failovers caused by transient network blips.
Question 5: A media company streams live video using two CDNs. During a failover event, viewers experience a 10-second buffering delay. Which architecture change would best minimize this delay?
- Increase origin server bandwidth
- Pre-warm the secondary CDN by pushing manifest and segment requests before failover (Correct answer)
- Reduce video bitrate encoding
- Switch from HLS to DASH protocol
Correct answer: Pre-warm the secondary CDN by pushing manifest and segment requests before failover
Pre-warming the secondary CDN ensures popular content is already cached, so when traffic shifts, the CDN can serve segments immediately without origin fetches.
Question 6: What distinguishes active-active multi-CDN from active-passive multi-CDN?
- Active-active uses only one CDN at a time; active-passive uses both simultaneously
- Active-active sends live traffic to multiple CDNs simultaneously; active-passive keeps the secondary CDN idle until failover (Correct answer)
- Active-active requires identical CDN configurations; active-passive allows divergent configs
- Active-active is only suitable for static content; active-passive works for dynamic content
Correct answer: Active-active sends live traffic to multiple CDNs simultaneously; active-passive keeps the secondary CDN idle until failover
In active-active mode, traffic is distributed across all CDNs continuously, while in active-passive mode, the secondary CDN only receives traffic when the primary fails.
Question 7: A multi-CDN operator needs to ensure consistent cache purge behavior across all providers when content is updated. Which approach is most reliable?
- Set very short TTLs so content naturally expires quickly across all CDNs
- Use a centralized purge API orchestration layer that calls each CDN provider's purge endpoint simultaneously (Correct answer)
- Rely on each CDN's default purge schedule
- Use different versioned URLs per CDN to avoid purge complexity
Correct answer: Use a centralized purge API orchestration layer that calls each CDN provider's purge endpoint simultaneously
A centralized purge orchestration layer ensures that invalidation requests are sent to all CDN providers atomically when content changes.
CDN Multi-CDN Strategy & Failover 2
Which DNS-based technique is most commonly used to distribute traffic across multiple CDN providers in a multi-CDN setup?