CDN Architecture & Components 3 — Questions and Answers
Question 1: What is the function of a CDN 'manifest file' in adaptive bitrate (ABR) streaming?
- It lists all PoP IP addresses for DNS failover
- It describes available video renditions and their segment URLs for the player (Correct answer)
- It contains the TLS certificate chain for edge servers
- It maps cache keys to storage buckets
Correct answer: It describes available video renditions and their segment URLs for the player
A manifest (e.g., HLS .m3u8 or DASH .mpd) enumerates each quality rendition and segment location so the player can switch bitrates dynamically.
Question 2: Which CDN architectural pattern uses geographically distributed 'scrubbing centers' to absorb volumetric DDoS traffic before it reaches PoPs?
- Anycast absorption
- BGP blackholing at origin
- DDoS mitigation via traffic scrubbing (Correct answer)
- Rate limiting at the edge
Correct answer: DDoS mitigation via traffic scrubbing
Scrubbing centers inspect and filter attack traffic in-line, passing only clean traffic onward to the CDN edge nodes.
Question 3: In CDN architecture, what is a 'cache key' and why does it matter?
- A cryptographic key used to encrypt cached objects
- The unique identifier (typically URL + selected headers) used to look up a cached object (Correct answer)
- A hardware key for tamper-proof storage
- The DNS record pointing to a CDN edge server
Correct answer: The unique identifier (typically URL + selected headers) used to look up a cached object
The cache key determines cache hit/miss logic; including the wrong headers (e.g., User-Agent) can fragment the cache and reduce hit rates.
Question 4: What is 'stale-while-revalidate' behavior in a CDN cache?
- The CDN refuses to serve content until the origin confirms freshness
- The CDN serves a stale cached object immediately while asynchronously fetching a fresh copy (Correct answer)
- The CDN deletes expired objects before they can be served
- The CDN downgrades HTTPS to HTTP during revalidation
Correct answer: The CDN serves a stale cached object immediately while asynchronously fetching a fresh copy
Stale-while-revalidate lets the CDN serve the old cached version instantly, then refresh it in the background, eliminating user-perceived latency.
Question 5: Which component in a CDN stack typically handles real-time log streaming and analytics aggregation across all edge nodes?
- Origin shield
- Edge-side scripting runtime
- Log aggregation pipeline (e.g., Kafka + ClickHouse) (Correct answer)
- Anycast router
Correct answer: Log aggregation pipeline (e.g., Kafka + ClickHouse)
High-volume edge logs are streamed via message queues and stored in columnar databases to support real-time analytics dashboards.
Question 6: What is 'private CDN peering' and how does it benefit a CDN provider?
- Encrypting traffic between CDN and origin at no extra cost
- Directly interconnecting with ISPs/IXPs to reduce transit costs and improve latency (Correct answer)
- Hosting edge nodes inside enterprise data centers
- Using dedicated MPLS circuits between PoPs
Correct answer: Directly interconnecting with ISPs/IXPs to reduce transit costs and improve latency
Private peering at Internet Exchange Points (IXPs) allows CDNs to exchange traffic directly with ISPs, bypassing expensive transit links.
Question 7: How does a CDN handle a 'cache MISS' for a request to a static asset?
- It returns a 404 error to the client
- It fetches the asset from the origin or parent cache, caches it, then serves it to the client (Correct answer)
- It redirects the client directly to the origin server
- It serves the nearest stale object regardless of TTL
Correct answer: It fetches the asset from the origin or parent cache, caches it, then serves it to the client
On a cache miss the edge node acts as a reverse proxy, fetching the asset from upstream, storing it locally, and forwarding it to the client.
CDN Architecture & Components 3
What is the function of a CDN 'manifest file' in adaptive bitrate (ABR) streaming?