The Path of One Request
One request to a CDN domain passes DNS, the Akamai edge, and the origin load balancer. Why "how long until users see the new file" has no single answer.
A request sent to cdn.example.com passes three layers: DNS, the CDN edge, and the load balancer at the origin.
I first drew this picture to answer one question: “After I upload a file to the bucket, how long until users see the new version?”
- DNS:
cdn.example.compoints to the Akamai edge hostname with a CNAME (Akamai Property: One Edge Config). - Akamai edge: if it has a copy, it replies at once. If not, it fetches from the origin.
- Load balancer: it hands the request to the right bucket by path (How the Load Balancer Picks a Backend).
- Several hostnames share one property, so they share the same origin and the same rules.
- The origin is not one server. It is a load balancer. Behind it are several buckets and one proxy service (Load Balancer: One Entrance, Many Backends by Rule).
After I drew it, I saw that the question has no single answer. The answer depends on the TTL of each layer on the path (TTL Is Set in Three Places).
To answer “how long until it updates?”, walk the path and ask each layer for its TTL.
Related: Load Balancer: One Entrance, Many Backends by Rule, Akamai Property: One Edge Config, How the Load Balancer Picks a Backend, TTL Is Set in Three Places. Or go back to the series overview.