Content Delivery Networks - CDN Cheat Sheet

Updated 2026-04-30

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Content Delivery Networks (CDNs) are globally distributed networks of edge servers that cache and deliver web content from locations nearest to end users, dramatically reducing latency and origin server load. CDNs sit between users and origin servers, serving as intelligent reverse proxies that make routing decisions based on real-time performance metrics, geographic proximity, and server health. The fundamental trade-off in CDN architecture is between cache hit ratio (how often content is served from cache) and content freshness — this tension shapes every caching policy, TTL setting, and invalidation strategy you'll configure.

What This Cheat Sheet Covers

This topic spans 15 focused tables and 114 indexed concepts, 108 flashcards. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.

Table 1: Core CDN Architecture ComponentsTable 2: Caching Strategies and TTL ConfigurationTable 3: Cache Invalidation and Purging MethodsTable 4: Request Routing and Load BalancingTable 5: Edge Performance OptimizationTable 6: Image and Video DeliveryTable 7: Security Features at CDN EdgeTable 8: Cache Control HeadersTable 9: Edge Computing and FunctionsTable 10: Origin Server OptimizationTable 11: Advanced Caching PatternsTable 12: Monitoring and Performance MetricsTable 13: CDN Configuration and ManagementTable 14: Content-Specific OptimizationsTable 15: Major CDN Providers (2026)

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Table 1: Core CDN Architecture Components

The building blocks every CDN is assembled from, traced along the path a request actually takes. Edge servers at distributed PoPs are where users land; origin shield and tiered caches sit behind them to shelter the origin; and anycast, DNS routing, and the cache key decide which edge answers and what counts as the "same" cached object. Get the cache key wrong and your hit ratio collapses no matter how good the rest of the architecture is.

Component	Example	Description
Edge Server (PoP)	`cdn.example.com` `→ edge-sjc15.cdn.net`	• Geographically distributed cache server at a Point of Presence • serves cached content to nearby users and fetches from origin on cache miss
Origin Server	`origin.example.com:443`	• Source-of-truth server hosting original website content • CDN fetches content here on cache misses and periodically revalidates
Origin Shield	Edge tier → Shield → Origin	• Additional caching layer between edge servers and origin that consolidates requests • dramatically reduces origin load by creating a three-tier hierarchy (Edge → Shield → Origin).
Tiered Cache	Regional cache in Singapore serves Asia-Pacific edges	• Hierarchical caching architecture with regional mid-tier caches • edge servers check regional cache before hitting origin, improving cache hit ratio for multi-region deployments
Anycast Routing	Same IP `203.0.113.1` routes to nearest PoP	• Network routing method where multiple servers share one IP address • BGP automatically routes users to the nearest healthy edge server based on network topology
DNS-based Routing	GeoDNS returns `edge-eu.cdn.net` for EU	• Traditional CDN routing that returns different IP addresses based on user's geographic location or latency • DNS resolver determines which edge server to use
Reverse Proxy	CDN terminates TLS, fetches from origin HTTP	• Intermediary server that sits in front of origin servers • CDN acts as reverse proxy handling client connections while communicating separately with origin
Cache Key	`GET /api/data?id=5` cache key: `url+id`	• Identifier used to store and retrieve cached objects • typically constructed from URL, query params, headers (Vary), cookies — cache key design directly impacts cache hit ratio

Table 2: Caching Strategies and TTL Configuration

This is where you tune the freshness-versus-load trade-off, mostly through Cache-Control directives. TTL settings like max-age and s-maxage decide how long content stays fresh and whether the edge and the browser get different lifetimes, while stale-while-revalidate and stale-if-error let you keep serving instantly even when content is expired or the origin is down. The choices range from caching everything aggressively to bypassing the cache entirely for personalized data.

Strategy	Example	Description
Max-age TTL	`Cache-Control: max-age=3600`	• Specifies how many seconds content remains fresh • after expiration CDN must revalidate with origin before serving — balance freshness needs vs origin load

The rest of this section is part of the full cheat sheet

Table 3: Cache Invalidation and Purging Methods

Caching is easy; knowing when to throw cached content away is the hard part. These methods range from surgical single-URL purges to the nuclear full-cache flush, with tag-based and wildcard purges sitting in between for logical grouping. The standout insight: for immutable assets, versioning the URL is almost always better than purging — a new filename sidesteps invalidation entirely, and soft or instant purges handle the cases where you truly must evict live content.

Method	Example	Description
URL Purge	Purge `/images/logo.png`	• Invalidates cached content for specific URL across all edge servers • typically completes in seconds to minutes depending on CDN architecture — most precise purge method

The rest of this section is part of the full cheat sheet

Table 4: Request Routing and Load Balancing

Before a CDN can serve content, it has to decide which edge a user reaches — and these techniques are how that decision gets made. They climb in sophistication from blunt round-robin DNS and GeoDNS up through latency-based routing, anycast, and full GSLB that weighs health, load, and geography together. The bottom rows shift focus to the origin side, where pooling and health checks keep traffic flowing even when a backend dies.

Technique	Example	Description
GeoDNS Routing	DNS returns closest edge IP by location	• Geographic-based DNS resolution that directs users to nearest regional edge server • uses client's DNS resolver location (not always accurate) to determine proximity

The rest of this section is part of the full cheat sheet

Table 1: Core CDN Architecture Components

Component	Example	Description
Edge Server (PoP)	`cdn.example.com` `→ edge-sjc15.cdn.net`	• Geographically distributed cache server at a Point of Presence • serves cached content to nearby users and fetches from origin on cache miss
Origin Server	`origin.example.com:443`	• Source-of-truth server hosting original website content • CDN fetches content here on cache misses and periodically revalidates
Origin Shield	Edge tier → Shield → Origin	• Additional caching layer between edge servers and origin that consolidates requests • dramatically reduces origin load by creating a three-tier hierarchy (Edge → Shield → Origin).
Tiered Cache	Regional cache in Singapore serves Asia-Pacific edges	• Hierarchical caching architecture with regional mid-tier caches • edge servers check regional cache before hitting origin, improving cache hit ratio for multi-region deployments
Anycast Routing	Same IP `203.0.113.1` routes to nearest PoP	• Network routing method where multiple servers share one IP address • BGP automatically routes users to the nearest healthy edge server based on network topology
DNS-based Routing	GeoDNS returns `edge-eu.cdn.net` for EU	• Traditional CDN routing that returns different IP addresses based on user's geographic location or latency • DNS resolver determines which edge server to use
Reverse Proxy	CDN terminates TLS, fetches from origin HTTP	• Intermediary server that sits in front of origin servers • CDN acts as reverse proxy handling client connections while communicating separately with origin
Cache Key	`GET /api/data?id=5` cache key: `url+id`	• Identifier used to store and retrieve cached objects • typically constructed from URL, query params, headers (Vary), cookies — cache key design directly impacts cache hit ratio

Table 2: Caching Strategies and TTL Configuration

Strategy	Example	Description
Max-age TTL	`Cache-Control: max-age=3600`	• Specifies how many seconds content remains fresh • after expiration CDN must revalidate with origin before serving — balance freshness needs vs origin load

Table 3: Cache Invalidation and Purging Methods

Method	Example	Description
URL Purge	Purge `/images/logo.png`	• Invalidates cached content for specific URL across all edge servers • typically completes in seconds to minutes depending on CDN architecture — most precise purge method

Table 4: Request Routing and Load Balancing

Technique	Example	Description
GeoDNS Routing	DNS returns closest edge IP by location	• Geographic-based DNS resolution that directs users to nearest regional edge server • uses client's DNS resolver location (not always accurate) to determine proximity