CDN Junior
What is a 'Point of Presence' (PoP) in the context of a CDN, and how does it differ from a traditional data center?
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A centralized hub that processes all database writes before replicating them out globally.
A backup site that mirrors the primary data center for disaster recovery purposes alone.
A cluster of edge servers placed near users to cache and serve content with low latency.
A single large facility that stores an application's complete data and all its services.
What is a PoP (Point of Presence), and how does it differ from a single edge server?
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A PoP is a location housing many edge servers and gear; an edge server is one machine inside.
A PoP is a single high-capacity server and an edge server is a smaller regional replica of it.
A PoP is the origin's regional mirror while an edge server only handles DNS lookups for users.
A PoP is a software router while an edge server is the physical hardware that runs caching.
What is a CDN and what are the primary problems it solves for a modern web application?
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A distributed server network that caches content near users to cut latency and offload origin.
A DNS provider that resolves domain names quickly by storing records in many locations now.
A managed database service that replicates writes across regions to ensure data durability.
A security gateway that inspects every request to block attacks before reaching the backend.
What is an 'Edge Server' (or PoP) and how does it differ from an 'Origin Server'?
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The edge caches and serves content near users; the origin is the authoritative content source.
The edge generates dynamic pages; the origin merely forwards static assets to the browsers.
The edge stores the original files; the origin only handles overflow traffic during spikes.
The edge resolves DNS queries for clients; the origin balances load across the edge servers.
What is Time To First Byte (TTFB), and how does putting a CDN in front of your origin affect it?
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Time until the page fully renders; a CDN improves it only for dynamic content.
Time until the first response byte arrives; a CDN edge cache usually lowers it.
Time to establish a TCP connection; a CDN has no measurable effect on it at all.
Time to download the full response; a CDN raises it due to extra network hops.
What is the difference between a 'Push CDN' and a 'Pull CDN', and in what scenarios would you choose one over the other?
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Push runs at the origin server; pull runs entirely within the user's browser cache.
Push caches dynamic content; pull caches only static images and large video files.
Push fetches content on first request; pull replicates the entire origin nightly.
Push uploads content to the CDN ahead of time; pull fetches it on first cache miss.
What is 'Hotlinking' and how can a CDN prevent other sites from stealing your bandwidth?
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Embedding your assets on another site; the CDN blocks it by checking the Referer header.
Caching stale content on third parties; the CDN prevents it by shortening the TTL on every object.
Hijacking your DNS records remotely; the CDN prevents it by enforcing DNSSEC across all the zones.
Scraping your rendered HTML pages; the CDN prevents it by rate-limiting all known crawler IP ranges.
What metrics are most important for evaluating a CDN's effectiveness?
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Origin CPU usage, RAM consumption, disk I/O, and database query times only.
HTML page size, image compression ratio, script bundle count, and font loads.
Number of edge POPs, total contract cost, vendor SLA tier, and brand reputation.
Cache hit ratio, latency or TTFB, throughput, and error rates across edge locations.
How does a CDN decide when to fetch a new version of a file from the origin?
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When the object's TTL expires or it is purged, it revalidates or re-fetches from the origin
When a fixed scheduled interval elapses, the edge discards all cached objects and reloads them together
When the origin server actively pushes a notification to every edge node telling it the file has changed
When the edge node compares each stored file's checksum against the origin on every incoming user request
How does the origin use Cache-Control headers to signal the CDN what is cacheable and for how long?
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Directives like max-age, s-maxage, private and no-store set cacheability and freshness
The Host header lists which edge regions may cache the object and for how many minutes each one may keep it
The origin embeds expiry timestamps inside the response body which the CDN parses to decide caching duration
The origin sets a Content-Length value that tells each edge node exactly how many seconds the object stays fresh