In-Depth Investigation of CDN: Part 2

A nearby cache is useful only if it serves an acceptable version of the content. This lesson connects freshness rules with deployment choices, then compares a managed CDN with a purpose-built delivery network.

For each option, ask what happens during an origin update, a disconnected proxy, and a traffic surge. Those cases expose the coordination and spare capacity that the design needs.

Content consistency in CDN

Define how stale each content class may be. A versioned static asset and a frequently updated page can use different rules. Push and pull determine how copies arrive; freshness, invalidation, and failure policies determine when they may be served.

Periodic polling

With periodic polling, a proxy checks the origin at a fixed time-to-refresh (TTR) interval. It can detect changes without waiting for a user request, but checks for unpopular or unchanged objects consume resources. This is one refresh policy, not a requirement of all pull caches.

Time-to-live (TTL)