Content Delivery Networks (CDN) Cheat Sheet

Explains how CDNs cache and serve content at the edge, key Cache-Control headers, example configuration, and the benefits of using one.

2 PagesBeginnerMar 15, 2026

Core CDN Concepts

Terminology used across every CDN provider.

Edge server / PoP- Point of Presence — a distributed server that caches and serves content near users
Origin server- Your actual backend that the CDN pulls content from on a cache miss
Cache hit/miss- Hit = edge had the content; Miss = it fetched and cached from origin
TTL- Time to Live — how long an edge server keeps a cached object before revalidating
Purge/Invalidation- Manually evicting cached content from edge nodes before its TTL expires
Origin Shield- Extra caching layer between edges and origin to reduce origin load on misses
Anycast routing- Routes a request to the nearest/healthiest edge location using one shared IP

Cache-Control Headers

Three common caching policies and conditional revalidation.

http

# Cache aggressively — for versioned/hashed static assets (immutable content)Cache-Control: public, max-age=31536000, immutable# Cache but revalidate — for HTML that changes but should still hit cacheCache-Control: public, max-age=0, must-revalidate# Never cache — for sensitive/dynamic API responsesCache-Control: private, no-store# Combine with ETag for conditional revalidationETag: "33a64df5"# Client's next request:If-None-Match: "33a64df5"# Server replies 304 Not Modified if unchanged (saves bandwidth)

Example CDN Configuration

A CloudFront-style distribution with a bypassed API path.

json

{  "Origins": [{ "DomainName": "origin.example.com", "Id": "primary-origin" }],  "DefaultCacheBehavior": {    "TargetOriginId": "primary-origin",    "ViewerProtocolPolicy": "redirect-to-https",    "CachePolicyId": "CachingOptimized",    "Compress": true  },  "CacheBehaviors": [    {      "PathPattern": "/api/*",      "TargetOriginId": "primary-origin",      "CachePolicyId": "CachingDisabled"    }  ]}

Benefits & When to Use

Why almost every production site sits behind a CDN.

Lower latency- Content served from a nearby edge instead of a distant origin server
Reduced origin load- Cache absorbs repeat requests, protecting the origin from traffic spikes
DDoS mitigation- CDNs absorb and filter large-scale traffic at the edge before it reaches origin
Bandwidth savings- Origin egress traffic drops significantly as cache hit ratio increases
Global availability- Multiple PoPs provide redundancy if one region has an outage
TLS termination at the edge- Faster HTTPS handshakes closer to the user

Pro Tip

Set a long max-age plus immutable on assets with content-hashed filenames (e.g. app.a3f9c2.js) so browsers and edge caches never revalidate them — then bust the cache simply by deploying a new build with a different hash, never by purging.

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