5.3.1 CDN
A content delivery network stores copies of assets at PoPs. The user hits the nearest edge instead of your origin.
Why it matters
Origin bandwidth and latency dominate global apps. A CDN cuts TTFB for images, JS, and cacheable APIs.
How it is used
Put the CDN in front of object storage or the app. Set Cache-Control. Purge on deploy when filenames are not hashed. Never cache authenticated HTML unless you know the keying rules.