# Demonstration: One File, Two Containers, One Network — Automatically

## OBSERVE

```yaml
services:
  web:
    image: nginx:alpine
    ports:
      - "8080:80"
  cache:
    image: redis:alpine
```

## HYPOTHESIS

Predict: without running `docker network create` yourself, will `web` be able to reach `cache`
by name after `docker compose up`?

## INSPECT

```
$ docker compose up -d
$ docker compose exec web sh -c "wget -qO- http://cache:6379/ 2>&1 | head -1" 
```

(Redis doesn't speak HTTP, so this specific request looks odd, but the connection ITSELF
succeeding or failing tells you whether name resolution and network reachability work — a
`Connection refused` here would mean it REACHED `cache` but Redis rejected the protocol
mismatch, which is actually proof the network worked.)

## CHANGE

```
$ docker compose ps
NAME        IMAGE          STATUS
web-1       nginx:alpine   Up
cache-1     redis:alpine   Up
$ docker network ls | grep compose
xyz123   myproject_default   bridge
```

Compose created a network automatically, named after the project directory, with no manual step.

## VERIFY

```
$ docker compose down
$ docker network ls | grep compose
(nothing)
```

`docker compose down` cleaned up EVERYTHING Compose created — containers AND the network — in
one command.

## Instructor Notes

**Demo goal:** Show the automatic networking as a real, observable fact (a real network exists,
named and scoped to the project) rather than an assumed convenience.

**Approximate timing:** 8 minutes live.

**Common mistake to watch for:** forgetting `docker compose down` and accumulating orphaned
networks/containers across multiple exercises — a good habit to reinforce explicitly.