Interconnection · Lesson 11

Why can a nearby server answer a request?

A CDN (Content Delivery Network) distributes cached content across edge locations. A user can often receive a popular file from a nearby point of presence instead of waiting for the origin server on every request.

Move the answer closer

A cache can shorten the journey.

The origin server is the authoritative source for a resource. A CDN places copies of cacheable resources at edge locations, which are servers positioned near groups of users.

When a request reaches an edge location, a cache hit can return the stored response immediately. On a cache miss, the edge fetches the resource from the origin, serves it to the user, and may keep a fresh copy for later requests.

Nearby does not mean authoritative.The edge serves a copy according to cache rules. The origin remains the source that can provide or update the resource.

Build the model

Four CDN pieces

01

Origin

The authoritative server or service that owns the resource.

02

Edge location

A nearby delivery point that can serve cached content.

03

Cache policy

Rules that decide what can be stored and for how long.

04

Cache miss

A request that requires the edge to fetch from the origin.

Mini experiment

Follow a request

Select the state of the edge cache and see where the response comes from.

DELIVERYEdge cache hit

The nearby edge already has a fresh copy and returns it to the user.

The origin is not contacted for this request.

Knowledge check

Test your CDN model

Answer five questions. The answer order changes each time.

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