Stencel Academy

How Infrastructure Works

A free, interactive course from Stencel Academy. Follow a real request across a living map of the internet — DNS, HTTP, TCP/TLS, routing, load balancers, databases, caches, containers and orchestration — and watch how infrastructure works until it finally clicks.

Choose your learning path

• Prompt Engineer — Call any API and know exactly what happened. For prompt & AI engineers. Follow a request from your laptop to a server and back — DNS, ports, HTTP, JSON, and the auth token that opens the door.
• Product Builder — Ship and debug over real networks. For builders shipping real products. Everything in Prompt Engineer, plus how bytes actually move — addresses, routing, TCP, TLS, firewalls, and load balancers.
• Infra Operator — Run the services behind the app. For engineers who run production. Adds the server room: reverse proxies, databases, caches, queues & workers, containers, and orchestration.
• Prompt Architect — Design the full AI product stack. For future AI architects. The complete arc: cloud & infrastructure as code, CI/CD, observability — and the capstone: one prompt traversing the entire stack.

All 22 lessons

• The Round Trip — Watch one API call cross the internet and return. Every API call is a message to someone else's computer — you can watch it go and come back.
• Clients & Servers — A server is a computer running a listening process. A server is an ordinary computer, always on, running processes that listen for other computers.
• Names to Addresses — Turn a name into an address you can reach. DNS turns names into IP addresses; resolvers cache answers for TTL seconds, so repeats are instant.
• Ports: Many Doors, One Machine — One machine, many ports — each a different process. A port is a numbered door into one process; 'connection refused' means nobody is listening there.
• Anatomy of HTTP — See the moving parts inside one HTTP exchange. Every HTTP exchange is request line + headers + body out, status code + headers + body back.
• APIs, JSON & Tokens — Call a real API: token in, JSON out. APIs speak JSON both ways; the bearer token is your key, and usage tokens are the bill.
• Addresses & Networks — Two addresses, one laptop: private inside, public at the edge. Your private address works only at home; NAT lets one public address speak for the whole network.
• Packets & Routing — Follow a packet hop by hop across the internet. There is no direct wire — every packet is handed router to router, and each hop adds latency.
• TCP: The Reliable Pipe — Watch TCP build a reliable pipe from unreliable packets. TCP numbers every byte and acknowledges every segment — a reliable pipe built on an unreliable network.
• TLS & Certificates — Prove who you're talking to, then encrypt everything. The certificate proves the server's name; the chain of trust proves the certificate. Then everything is encrypted.
• Firewalls & Security Groups — Every packet is interrogated at the door. Firewalls default-deny: a port is closed unless a rule opens it, and who may knock matters.
• Load Balancers — One address, many machines — the balancer decides. One public address fronts a pool; health checks decide who's alive, round-robin decides who answers.
• Web Servers & Reverse Proxies — Meet the process that actually answers the port. The port answers to nginx, not your app — a reverse proxy fronts, shields, and forwards to the real process.
• Databases: Where State Lives — Give your stateless app one place that remembers. Apps stay stateless so the database can be the one place that remembers — and replicas keep a live copy.
• Caches & CDNs — The fastest query is the one you never make. A cache answers from memory in microseconds; misses fall through to the database. TTLs keep stale answers honest.
• Queues & Workers — Answer the user now; do the slow work later. Return 202, enqueue the job, let workers grind — the user never waits on slow work.
• Containers & Images — Ship the whole environment, not just the code. An image freezes app plus environment; docker run thaws it anywhere, mapping host ports to the container.
• Orchestration — Declare the destination; let the orchestrator drive. You declare desired state; the control plane watches reality and reschedules pods until the two match.
• Cloud & Infrastructure as Code — Describe your data center in a file, then make it real. The data center is a reviewable, versioned text file — plan shows the diff, apply makes it real.
• CI/CD Pipelines — Push code; watch machines build, test, and ship it safely. Humans review the change; the pipeline builds, tests, and ships it — and a red test stops production cold.
• Logs, Metrics & Traces — Find the slow hop with logs, metrics, and traces. Logs say what happened, metrics say how much, traces say where — you can't fix what you can't see.
• Capstone: The AI Product Stack — Watch one prompt cross every layer you have learned. Every lesson was one hop of this map — a prompt architect designs the whole board: latency, cost, scale.

Learn how internet infrastructure works by tracing real requests and watching a live map of the network move — no walls of text. Runs entirely in your browser — nothing to install.