CDN Architecture & Components 4 — Questions and Answers
Question 1: What is the purpose of 'Edge Side Includes' (ESI) in CDN architecture?
- To embed CDN configuration directly in HTML meta tags
- To assemble page fragments with different cache TTLs at the edge before delivery (Correct answer)
- To execute JavaScript at edge nodes for server-side rendering
- To inject security headers into cached responses
Correct answer: To assemble page fragments with different cache TTLs at the edge before delivery
ESI allows the CDN to cache page components independently and stitch them together at the edge, so personalized and cached sections coexist.
Question 2: Which TCP optimization technique do CDN edges commonly use to improve throughput for users with high-latency connections?
- TCP Fast Open and larger initial congestion windows (Correct answer)
- Reducing the TCP receive buffer to zero
- Disabling Nagle's algorithm globally
- Forcing TCP Reno instead of CUBIC
Correct answer: TCP Fast Open and larger initial congestion windows
TCP Fast Open and increased initial congestion windows reduce the number of round trips needed before the connection reaches full throughput.
Question 3: In a CDN context, what is 'edge compute' or 'serverless at the edge' primarily used for?
- Running origin application databases closer to users
- Executing lightweight request/response logic (e.g., A/B testing, auth, personalization) at PoPs (Correct answer)
- Storing large media files at edge nodes permanently
- Replacing the CDN's load balancing layer
Correct answer: Executing lightweight request/response logic (e.g., A/B testing, auth, personalization) at PoPs
Edge compute platforms (e.g., Cloudflare Workers, Fastly Compute) run small scripts at PoPs to customize responses without a round trip to the origin.
Question 4: What does 'Cache-Control: s-maxage' specifically control in a CDN environment?
- The maximum age of cookies set by the origin
- How long shared (proxy/CDN) caches may store a response, independently of browser cache TTL (Correct answer)
- The timeout for SSL session resumption at the edge
- The number of PoPs that may cache a given object
Correct answer: How long shared (proxy/CDN) caches may store a response, independently of browser cache TTL
s-maxage overrides max-age for shared caches like CDNs, letting operators set different CDN and browser TTLs in the same header.
Question 5: Which CDN feature allows operators to instantly remove a cached object from all edge nodes worldwide?
- Cache warming
- Surrogate-key / cache tag purging (Correct answer)
- TTL extension
- Conditional GET revalidation
Correct answer: Surrogate-key / cache tag purging
Surrogate keys (or cache tags) group related objects so a single API call purges all tagged content across the entire CDN fleet instantly.
Question 6: What is the significance of 'PoP diversity' when designing CDN redundancy?
- Having PoPs in many countries ensures compliance with local data laws only
- Spreading PoPs across different ISPs and buildings ensures no single outage eliminates all local coverage (Correct answer)
- Diversity means each PoP must run a different operating system
- PoP diversity only matters for video streaming workloads
Correct answer: Spreading PoPs across different ISPs and buildings ensures no single outage eliminates all local coverage
PoP diversity across carriers and facilities means a fiber cut, power failure, or ISP outage at one PoP doesn't remove CDN coverage for a region.
Question 7: How does a CDN typically handle 'range requests' (e.g., HTTP Range: bytes=0-1023) for large files?
- It rejects range requests and forces full-file downloads
- It fetches and caches the full file from origin, then serves the requested byte range from cache (Correct answer)
- It passes range requests directly to the origin without caching anything
- It splits the file into fixed 1 MB chunks cached separately
Correct answer: It fetches and caches the full file from origin, then serves the requested byte range from cache
Most CDNs fetch and cache the complete object on first miss, then fulfill byte-range requests from the cached copy to maximize cache utility.
CDN Architecture & Components 4
What is the purpose of 'Edge Side Includes' (ESI) in CDN architecture?