Content Delivery Networks

A content delivery network, or CDN, delivers content through distributed infrastructure. Instead of sending every request to one origin server, a CDN routes a request to an edge location that can serve it.

The edge location may already hold a reusable response. That is a cache hit. The edge returns the response without asking the origin. If no usable response exists, a cache miss occurs. The CDN fetches from the origin or another cache layer, forwards the response, and may store it for later requests.

This design can reduce latency, network traffic, and origin load. It also creates distributed state. You must decide what can be cached, how long it stays fresh, which request details create distinct variants, and how updates replace old content.

The request path

A typical request follows this path:

A user agent resolves the application hostname.
Request routing selects a suitable edge location.
The edge builds a cache key from the request.
The edge looks for a stored response under that key.
A hit returns from the edge.
A miss travels toward the origin, possibly through an upper-tier cache.
The response returns to the user and may populate caches along the path.

The selected edge is not always the geographically nearest site. A provider can consider network latency, reachability, capacity, and policy. The practical goal is a suitable delivery point, not a dot that looks closest on a map.

The origin remains the authoritative source for the content. An origin can be a web server, object store, application service, or another delivery system. The CDN sits between user agents and that origin. It does not remove the need to operate the origin correctly.

Content Delivery Networks

Content Delivery Networks

The request path

A CDN is more than a cache

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