+How a request actually travels

Request journey.

Six stops between typing a URL and getting a 200. Break any of them and see exactly where the request gives up.

One request, six stops

Browser

You type https://app.lab. Before a single byte of HTTP is sent, the browser needs an IP address, a route to it, and a trusted TLS connection.

What usually goes wrong

A stale DNS cache keeps using an old address
A system proxy setting sends traffic somewhere unexpected
A wrong system clock makes every certificate look invalid

How to check

ip addr

What it looks like in a log

DevTools → Network: (failed) net::ERR_NAME_NOT_RESOLVED

Fault injection

all healthy

Break app.lab A recordBreak Workstation gatewayBreak Proxy upstream portBreak Proxy TLS certificateBreak weekend-api.service at bootBreak Backend log retentionBreak Database host in connection string

Timing

HTTP/1.1 200 OK

DNS lookup4 msapp.lab → 10.42.20.10
Route / connect1 msRoute to 10.42.20.10 available
Proxy accepts1 msReverse proxy accepted HTTPS on port 443
TLS handshake14 msTLS OK · CN=app.lab · valid to 2027-03-01
Application18 ms10.42.20.20:3000 → weekend-api accepted the request
Database query6 ms10.42.20.30:5432 → query OK

Healthy. 44 ms end to end.

HTTP/1.1 200 OK
Server: lab-proxy

{"status":"ok","service":"weekend-api"}

NOC gremlin: Everything’s green. Flip a switch. You know you want to.