# Demonstration: `run` Creates, `exec` Reaches In

## OBSERVE

```
$ docker run -d --name web nginx:alpine
$ docker ps --format '{{.Names}}'
web
```

One container exists.

## HYPOTHESIS

Predict: will `docker exec web echo hello` create a SECOND container?

## INSPECT

```
$ docker exec web echo hello
hello
$ docker ps --format '{{.Names}}'
web
```

Still exactly one container — `exec` ran a new command INSIDE the existing one, it never
created anything new.

## CHANGE

Now actually run the same image again:

```
$ docker run -d --name web2 nginx:alpine
$ docker ps --format '{{.Names}}'
web2
web
```

Now two containers exist — because `run`, unlike `exec`, always creates a NEW container.

## VERIFY

```
$ docker logs web | tail -3
$ docker inspect web --format '{{.State.Running}}'
true
```

Both containers are independent, each with their own logs and state — exactly as Module 2's
"one image, many containers" demonstration showed.

## Instructor Notes

**Demo goal:** Directly contrast `run` and `exec`'s effect on the container COUNT — this is the
most common early confusion and deserves a side-by-side comparison.

**Approximate timing:** 8 minutes live.

**Common mistake to watch for:** trying to `exec` into a container that isn't running yet
(`exec` requires an ALREADY-running target) — a good moment to connect back to `docker ps`
first.