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World D3: Lockers & Phone Lines

Bind mounts and tmpfs

You will learn: to share a laptop folder with a container, and to keep data in memory only.

Checked with Docker Engine 29 on 31 Oct 2026

The problem

Your laptop~/shop

Lunchboxes (containers)

  • siterunning
    from shop-site:1.0 8080→80

Frozen packs (images)

  • nginx:1.30-alpine8 layers · 93.5MB
  • shop-site:1.09 layers · 92.6MB · in use

You fixed the shop page on your laptop. The box still shows the old page. It was baked into the image. Rebuild for every typo?

Watch

A bind mount: Your own shelf: a folder on your laptop, opened inside the container. Edits show up at once. slides your own shelf into the lunchbox. The box sees your laptop folder itself, not a copy. Tap the pieces in order.

Tap the pieces in the right order.

…

Try it

Run site with your ./site shelf. Then change index.html and curl again.

Your laptop~/shop

  • No open hatches

Lunchboxes (containers)

  • No containers yet

Frozen packs (images)

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

Check

site runs with :ro. Something in the box tries to save a file in that folder. What happens?

Watch

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
  • postgres:18-alpine9 layers · 433MB

tmpfs: A note on a whiteboard: data kept in memory only. Every stop wipes it. is a note on a whiteboard: memory only. It is fast and never touches the disk. Every stop wipes it.

Predict

Four places to keep a file. Guess first, then run it.

Where does each file live? Guess what stays, then run it.

$ docker run -d --name kedai -v kedai-data:/data -v ./menu:/menu --tmpfs /tmp/cache nginx:1.30-alpine

Question 1 of 2

Lunchbox: container kedai

  • Inside the lunchbox (writable layer)/app/today.txt
  • A note in memory (tmpfs)/tmp/cache/cache.bin

Outside the lunchbox

  • Locker kedai-data (volume)/data/orders.db
  • Your shelf ./menu (bind mount)/menu/menu.md

Next, you run:

Restart the container.

$ docker restart kedai

Pick Stays or Gone for every file first.

Check

Pick the right place for each job.

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

        You did it!

        You can now use bind mounts and tmpfs.

        Go deeper (optional)

        --mount type=bind,src=./site,dst=/data is the long form. It refuses a folder that doesn’t exist; -v quietly makes an empty one. On Docker Desktop, volumes are faster than bind mounts.

        Real rep (optional), in your own project folder:

        Real mission

        1. mkdir -p site && echo "<h1>Hello</h1>" > site/index.html
        2. docker run -d --name site -p 8080:80 -v ./site:/usr/share/nginx/html:ro nginx:1.30-alpine
        4. docker rm -f site

        0 of 4 steps done · Your ticks are saved.