CDN Cheat Sheet 2026

The 30 highest-yield CDN facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. 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? → Issue a cache purge/invalidation for the affected URLs
2. What is the benefit of root cause analysis? → Prevent recurrence
3. What is the purpose of a CDN's 'Shield' or 'Mid-tier Cache' architecture? → Consolidate cache MISS requests to a single POP before hitting origin
4. A company's CDN costs spike every weekend due to user-generated video uploads triggering transcoding and delivery. Which strategy best controls these costs? → Use scheduled off-peak transcoding jobs and set upload size limits
5. Which metric best measures viewer-perceived video quality during adaptive bitrate streaming? → Mean Opinion Score (MOS) or Video Multimethod Assessment Fusion (VMAF)
6. What is a common cause of CDN performance issues? → Overload or congestion
7. What is a 'positive security model' WAF approach? → Allowing only explicitly defined legitimate request patterns and blocking everything else
8. A sliding window rate limiter differs from a fixed window rate limiter in that it: → Prevents burst exploitation at window boundaries
9. How does SSL/TLS enhance CDN security? → Encrypt data transmission
10. In a multi-tier CDN hierarchy, what distinguishes a 'parent' cache from an 'edge' cache? → Edge caches fill cache misses from parent caches rather than the origin
11. In a multi-CDN deployment, which HTTP header should the origin always include to enable downstream CDN nodes to cache responses correctly and consistently? → Cache-Control with explicit directives (max-age, s-maxage)
12. Why is latency monitoring important? → Maintain fast delivery
13. Which of the following best describes a key competency required for cost optimization & traffic management in CDN practice? → Strong analytical skills combined with effective communication and ethical judgment
14. What is the role of a 'developer portal' in a CDN's API gateway ecosystem? → To provide documentation, API key management, and quota dashboards to API consumers
15. A CDN WAF is configured in 'monitor' mode. What is the effect on malicious traffic? → Traffic is allowed but logged for analysis
16. A global e-commerce site uses a CDN with 50 edge POPs. After a flash sale, they notice the CDN's cache hit ratio dropped to 20%. What is the most likely cause? → High request variance — too many unique URLs from personalization or query strings
17. Which CDN cost lever has the most direct impact on reducing 'cache fill' costs from origin to edge nodes? → Using origin shield (mid-tier caching) to consolidate origin requests
18. Which isolation technology do most CDN providers (e.g., Cloudflare Workers, Fastly Compute) use instead of containers for edge functions? → V8 Isolates
19. Which security mechanism allows a CDN to verify that a JWT token in an API request is valid before forwarding the request to the origin? → Edge-side JWT validation using the CDN's WAF or edge compute
20. What is a cache miss? → Content not found in cache
21. Which HTTP response header instructs browsers to only connect to a site over HTTPS for a specified duration, even if the user types HTTP? → Strict-Transport-Security
22. Which DNS attack exploits a vulnerable resolver to redirect users to a malicious IP by poisoning its cache? → DNS cache poisoning
23. What does a CDN 'token authentication' mechanism typically protect against? → Unauthorized hotlinking or direct URL sharing of protected assets
24. Which protocol is ACME (Automatic Certificate Management Environment) most commonly associated with? → Let's Encrypt certificate issuance automation
25. Which API gateway strategy helps prevent a 'noisy neighbor' tenant from degrading CDN API performance for other tenants? → Per-tenant rate limit isolation with dedicated counters
26. What is the primary purpose of CDN traffic shaping in a cost optimization context? → To prioritize or throttle specific traffic types to control bandwidth costs
27. Which CDN technique reduces startup latency for live video streams by pre-positioning the first few segments at edge nodes before viewers request them? → Segment prefetching
28. Which mechanism allows a CDN to serve content from a nearby PoP even when the authoritative PoP for that region is overloaded? → Anycast failover to an alternate PoP
29. What is 'token escalation' in the context of CDN security? → An attack where a low-privilege token is manipulated to gain access to restricted content
30. Which DNS-based technique is most commonly used to distribute traffic across multiple CDN providers in a multi-CDN setup? → GeoDNS with weighted records