Part 3 · Lesson 12 · Advanced

Web Servers & Reverse Proxies

Meet the process that actually answers the port.

In this interactive Infrastructure lesson from Stencel Academy you don't just read — you type real commands like systemctl status nginx, curl -v localhost and watch the machine respond on a live, animated map. It is part of the free How Infrastructure Works course.

Key takeaway: The port answers to nginx, not your app — a reverse proxy fronts, shields, and forwards to the real process.

Before this lesson

Builds on: Load Balancers.

What you'll practise

cat /etc/nginx/sites-enabled/promptd.conf — The one line that wires proxy to app.
ss -tlnp | grep 3000 — Proof promptd hides on loopback only.
nginx -t — Test config before you reload — never break prod.
curl -s localhost/healthz — The endpoint lb-01 polls to keep web-01 in rotation.

Terms you'll learn

reverse proxyupstreamloopback (127.0.0.1)TLS terminationsystemd service

Check your understanding

Who answers port 80 on web-01?

nginx, which forwards the request to promptd on 127.0.0.1:3000
promptd itself — it listens on port 80 directly
The load balancer lb-01 runs on web-01 and answers it

Open the interactive lesson →