World D1: First Containers

Image vs container

You will learn: how one image (a meal pack) fills many containers (lunchboxes).

Checked with Docker Engine 29 on 31 Oct 2026

The problem

Ali deleted the welcome page inside his lunchbox. Then he filled a fresh lunchbox from the same meal pack. The page is back! Bug or feature?

Watch

~ $ docker images                                                i Info →   U  In UseIMAGE               ID             DISK USAGE   CONTENT SIZE   EXTRAalpine:3.22         2e0b81d60597       12.9MB         3.88MB        nginx:1.30-alpine   0e52bd054126       93.5MB           27MB        ~ $ docker run -d --name lunch1 nginx:1.30-alpine2f1e4458ce8eeb100f4beb4a2a42307bc50f70777b97668cd744a843fd5270df~ $ docker run -d --name lunch2 nginx:1.30-alpine5e58aeadbf439542332dc96b9b89c8c3cab36fa6762c85b2147fbed0479af324~ $ docker psCONTAINER ID   IMAGE               COMMAND                  CREATED         STATUS         PORTS     NAMES5e58aeadbf43   nginx:1.30-alpine   "/docker-entrypoint.…"   3 seconds ago   Up 3 seconds   80/tcp    lunch22f1e4458ce8e   nginx:1.30-alpine   "/docker-entrypoint.…"   6 seconds ago   Up 6 seconds   80/tcp    lunch1

Your laptop`~`

No open hatches

Lunchboxes (containers)

No containers yet

Frozen packs (images)

alpine:3.221 layers · 12.9MB
nginx:1.30-alpine8 layers · 93.5MB

One frozen meal pack fills two lunchboxes. The pack is the : a template that never changes. Each is one box made from it.

Try it

Sort each card. Is it about the meal pack or the lunchbox?

Drag a card into a box. Or tap the card, then tap the box.

Try it

Fill two lunchboxes from one pack. Run docker run alpine:3.22 echo hi twice. Then type docker images.

Your laptop`~`

No open hatches

Lunchboxes (containers)

No containers yet

Frozen packs (images)

alpine:3.221 layers · 12.9MB
nginx:1.30-alpine8 layers · 93.5MB

Predict

You delete index.html inside lunch1. Then you look inside lunch2. Is index.html there?

Check

~ $ docker run -d --name lunch1 nginx:1.30-alpine2f1e4458ce8eeb100f4beb4a2a42307bc50f70777b97668cd744a843fd5270df~ $ docker run -d --name lunch2 nginx:1.30-alpine5e58aeadbf439542332dc96b9b89c8c3cab36fa6762c85b2147fbed0479af324~ $ docker exec lunch1 rm /usr/share/nginx/html/index.html~ $ docker exec lunch1 ls /usr/share/nginx/html50x.html~ $ docker exec lunch2 ls /usr/share/nginx/html50x.htmlindex.html

Your laptop`~`

No open hatches

Lunchboxes (containers)

No containers yet

Frozen packs (images)

alpine:3.221 layers · 12.9MB
nginx:1.30-alpine8 layers · 93.5MB

Proof! The page left lunch1 only. lunch2 still has it. docker exec runs a command inside a box. Lesson 6 has more.

You did it!

You can now tell a meal pack (image) from a lunchbox (container).

Go deeper (optional)

A container is its image plus a thin writable layer on top. Every change goes into that layer. Remove the box, and its layer goes too. The image underneath stays untouched.

Real rep (optional):

Real mission

Fill two boxes from one pack.
docker run alpine:3.22 echo hi
Run the same command once more.
See both boxes.
docker ps -a
See just one alpine pack.
docker images

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Image vs container

Your laptop~

Lunchboxes (containers)

Frozen packs (images)

Your laptop~

Lunchboxes (containers)

Frozen packs (images)

Your laptop~

Lunchboxes (containers)

Frozen packs (images)

Your laptop`~`

Your laptop`~`

Your laptop`~`