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Overview Microsoft’s current application-delivery service is Azure Front Door Standard or Premium. Azure CDN Standard from Microsoft (classic) is still operating for existing profiles but retires on 30 September 2027. It no longer supports new profile or domain onboarding. Migration status Microsoft provides a migration path from the classic CDN tier to Front Door Standard or Premium. Existing users should check certificate, domain, rules-engine, WAF, and automation compatibility before the retirement date. ...

Caching is one of the simplest ways to improve delivery. A cache saves a copy of a response so it can be served without a round trip to the origin. The core control surface is the Cache-Control header and the time-to-live (TTL). Freshness and validation determine when a cache can reuse a stored response and when it must contact the origin. Quick answers max-age sets freshness for private and shared caches. s-maxage overrides max-age in a shared cache such as a CDN. It does not change the browser’s freshness lifetime. Vary tells a cache which request headers selected the response. Each meaningful value can create a separate representation. Vary: * prevents normal reuse because the cache cannot prove that a later request is equivalent. no-cache allows storage but requires validation before reuse. no-store prohibits storage. Freshness vs validation A cache serves a response when it is fresh. Freshness comes from an explicit lifetime such as max-age or from an older Expires date. After freshness ends, a cache either revalidates or fetches again. ...

Synopsis This chapter defines multi-CDN and explains when the approach improves service outcomes. It describes benefits in availability, performance, and vendor risk, and it outlines added complexity in operations, security, and cost. A simple decision framework and a migration overview provide a practical start point. Definition Multi-CDN is the practice of serving the same property through more than one content delivery network under a single control plane. Requests are routed to one of several providers based on policy. Policies consider jurisdiction, health, performance, and cost in that order of precedence. Correctness and user experience remain the primary constraints. ...