Test Yourself!

mkdir -p ~/v5-ch4/ty/public ~/v5-ch4/ty/empty && cd ~/v5-ch4/ty
echo '<h1>BookNest</h1>' > public/index.html; head -c 10M /dev/urandom > big.bin
printf '%s\n' 'FROM alpine:3' 'COPY public /site/' > q2.Dockerfile
printf '%s\n' 'FROM alpine:3' 'ENTRYPOINT echo hello from' 'CMD ["cmd"]' > q3a.Dockerfile
printf '%s\n' 'FROM alpine:3' 'ENTRYPOINT ["echo", "hello from"]' \
  'CMD ["cmd"]' > q3b.Dockerfile
printf '%s\n' 'FROM alpine:3' 'COPY big.bin /tmp/big.bin' 'RUN rm /tmp/big.bin' > q4.Dockerfile
printf 'services:\n  app:\n    image: alpine:${TAG}\n' > compose.yaml; echo 'TAG=3.23' > .env
printf '%s\n' 'FROM docker.io/library/alpine:3' 'HEALTHCHECK CMD true' > q10.Dockerfile

# 1. Can one container reach another by name? (Sections 4.6.1 and 4.6.2)
#    Predict: which of the two pings resolves its target?
docker network create l3-q1 >/dev/null
docker run -d --name l3-q1a alpine:3 sleep 60 >/dev/null
docker run --rm alpine:3 ping -c1 -W1 l3-q1a 2>&1 | tail -1
docker run -d --name l3-q1b --network l3-q1 alpine:3 sleep 60 >/dev/null
docker run --rm --network l3-q1 alpine:3 ping -c1 -W1 l3-q1b | head -1
docker rm -f l3-q1a l3-q1b >/dev/null; docker network rm l3-q1 >/dev/null
# 2. Where does the directory end up? (Section 4.8.3)
#    Predict: /site/public/index.html or /site/index.html?
docker build -q -f q2.Dockerfile -t l3-q2 . >/dev/null && docker run --rm l3-q2 find /site
# 3. Shell form, then exec form, each run without and with an argument. (Sections 4.8.6, 4.8.7)
#    Predict: which of the four runs print "cmd" or "world"?
for f in q3a q3b; do docker build -q -f $f.Dockerfile -t l3-$f . >/dev/null
  docker run --rm l3-$f; docker run --rm l3-$f world; done
# 4. The file is deleted in the next layer. What did it cost? (Sections 4.7.1 and 4.9.1)
#    Predict: the size of each of the two layers,
#    and how much more disk the image takes than alpine:3.
docker build -q -f q4.Dockerfile -t l3-q4 . >/dev/null
docker history --format '{{.Size}}  {{.CreatedBy}}' l3-q4 | head -2 | cut -c 1-50
docker image ls --format '{{.Repository}}:{{.Tag}} {{.Size}}' \
  | grep -E '^(alpine:3|l3-q4:latest) '

# 5. nginx's image declares EXPOSE 80, and you run it without -p. (Sections 4.6.4, 4.8.6)
#    Predict: how many ports are published, and does the container's own IP answer?
docker run -d --name l3-q5 nginx:1.30-alpine >/dev/null; sleep 1
echo "published: $(docker port l3-q5 | wc -l)"
curl -s -o /dev/null -w '%{http_code}\n' "$(docker inspect -f \
  '{{.NetworkSettings.Networks.bridge.IPAddress}}' l3-q5)"; docker rm -f l3-q5 >/dev/null
# 6. An empty named volume, then an empty host folder, over nginx's web root. (Section 4.11)
#    Predict: what does each ls list, and what is left in the volume afterwards?
W=/usr/share/nginx/html
docker run --rm -v l3-q6:$W nginx:1.30-alpine ls $W
docker run --rm -v "$PWD/empty:$W" nginx:1.30-alpine ls $W
docker run --rm -v l3-q6:/data alpine:3 ls /data; docker volume rm l3-q6 >/dev/null
# 7. .env says 3.23; the shell says 3.24; then no .env at all. (Section 4.12.4)
#    Predict: the three image names.
docker compose -p l3-q7 config --images; TAG=3.24 docker compose -p l3-q7 config --images
docker compose -p l3-q7 --env-file /dev/null config --images 2>&1 | sed 's/.*msg=//'

# 8. Node.js with no signal handler as PID 1, without and with --init. (Sections 4.8.7, 4.17.8)
#    Predict: each container's exit code and how long docker stop takes.
N='setInterval(() => {}, 1000)'
docker run -d --name l3-q8a node:24-slim node -e "$N" >/dev/null
docker run -d --init --name l3-q8b node:24-slim node -e "$N" >/dev/null
for c in l3-q8a l3-q8b; do s=$SECONDS; docker stop $c >/dev/null
  echo "$c exit=$(docker inspect -f '{{.State.ExitCode}}' $c) after $((SECONDS - s)) s"; done
docker rm l3-q8a l3-q8b >/dev/null
# 9. Start with a 64 MB limit, then raise it to 256 MB. (Sections 4.2.6 and 4.17.2)
#    Predict: the swap limit, and whether the update succeeds.
docker run -d --name l3-q9 --memory 64m alpine:3 sleep 60 >/dev/null
docker inspect -f '{{.HostConfig.Memory}} {{.HostConfig.MemorySwap}}' l3-q9
docker update --memory 256m l3-q9 2>&1 | sed -E 's/[0-9a-f]{64}/<id>/'
docker rm -f l3-q9 >/dev/null
# 10. One healthcheck, built by Podman twice and by Docker once. (Section 4.19.2)
#     Predict: which of the three images keeps it?
podman build -q -f q10.Dockerfile -t q10:oci . >/dev/null 2>&1
podman build -q --format docker -f q10.Dockerfile -t q10:docker . >/dev/null 2>&1
for t in oci docker; do
  podman image inspect -f "podman $t: {{json .Config.Healthcheck}}" q10:$t; done
docker build -q -f q10.Dockerfile -t l3-q10 . >/dev/null
docker inspect -f 'docker: {{json .Config.Healthcheck}}' l3-q10