A Request End to End, and Debugging by Layer

Typing an address and pressing Enter sets off every protocol in this subject, in a fixed order, in well under a second. Knowing that order is what turns "the site is down" into a question with an answer: which step failed, at which layer, and which tool proves it.

The topic follows one HTTPS request from the address bar to the first byte of the page, then turns the stack into a method: start at the layer the symptom points to, prove each layer with one tool, and move one layer at a time. It places cloud components on the stack by the header each reads, applies the method twice, once on a laptop and once behind a load balancer, and counts the round trips a new connection pays before any data arrives.

How to design the service that answers the request, its API and its errors, belongs to the API Design subject.

By the end you can order the steps of opening an HTTPS page, name the layer a symptom points to, pick the tool that tests it, count round trips before the first byte, and place a cloud component at its layer.