Overview
Module: Module 1: Infrastructure & Addressing
Activity type: Lab (Practice)
Objective: Given a running Compose service, the learner can inspect health and logs, perform a controlled image update, and roll back to a known-good state with evidence.
Learn
Before you start
In plain words: Read this block, then try the next action. If you feel stuck, tap What this means.
- Reading complete
- Lesson Feynman teach-back drafted (you may refine after the lab)
In plain words: Big idea: - Reading complete
- Lesson Feynman teach-back drafted (you may refine after the lab)
Hands-on
Guided lab
In plain words: Do these steps in order, one time, without skipping. Each step should leave proof you can show later.
More detail: If a step fails, stop and use Break/fix instead of inventing a new path.
Use the Class 2 compose-lab web service (or recreate it). Goal: prove you can update an explicit image tag and roll back with commands, not vibes.
1
Record the current image identity (last-known-good).
Windows (CMD / PowerShell)
cd $HOME\compose-lab
docker compose ps
docker compose images
docker image inspect nginx:stable --format "Id={{.Id}} RepoTags={{.RepoTags}}"
Copy-Item compose.yaml compose.yaml.bak
curl.exe -s http://127.0.0.1:8080/ | findstr UNIQUE
Linux / macOS (Terminal)
cd ~/compose-lab
docker compose ps
docker compose images
docker image inspect nginx:stable --format 'Id={{.Id}} RepoTags={{.RepoTags}}'
cp compose.yaml compose.yaml.bak
curl -s http://127.0.0.1:8080/ | grep UNIQUE
Write the image ID and tag in the workbook. That is your rollback target.
In plain words: Loopback talks only to this computer. Ping 127.0.0.1 to check the local IP stack.
2
Run the acceptance test (before change).
Browser or curl must show your unique phrase. Record “PASS” + timestamp.
In plain words: Do this step fully, then check that it worked before the next one. Focus: Run the acceptance test (before change).
3
Change to another explicit tag, validate, pull, recreate.
Edit image: from nginx:stable to a newer explicit tag you choose from Docker Hub (example pattern nginx:1.27, pick one that exists today). Then:
Windows (CMD / PowerShell)
docker compose config
docker compose pull
docker compose up -d
docker compose ps
docker compose logs --tail=80 web
docker compose images
Linux / macOS (Terminal)
docker compose config
docker compose pull
docker compose up -d
docker compose ps
docker compose logs --tail=80 web
docker image inspect $(docker compose images -q web) --format '{{.RepoTags}} {{.Id}}'
In plain words: Compose is the recipe file that starts and stops your app group together.
4
Re-run the acceptance test.
curl the unique phrase again. If it fails, do not continue, roll back now.
In plain words: Do this step fully, then check that it worked before the next one. Focus: Re-run the acceptance test.
5
Simulate a bad update (nonexistent tag), then restore.
Windows (CMD / PowerShell)
# Temporarily set image: nginx:this-tag-does-not-exist-otacon
docker compose pull
docker compose up -d
docker compose ps
docker compose logs --tail=40 web
Copy-Item compose.yaml.bak compose.yaml -Force
docker compose pull
docker compose up -d
curl.exe -s http://127.0.0.1:8080/ | findstr UNIQUE
Linux / macOS (Terminal)
# edit image to nginx:this-tag-does-not-exist-otacon, then:
docker compose pull || true
docker compose up -d || true
docker compose ps
docker compose logs --tail=40 web
cp compose.yaml.bak compose.yaml
docker compose pull
docker compose up -d
curl -s http://127.0.0.1:8080/ | grep UNIQUE
In plain words: Loopback talks only to this computer. Ping 127.0.0.1 to check the local IP stack.
6
Fill a mini service contract (also use templates/service_contract.csv):
purpose: compose-lab nginx demo
image/version: (tag + image id)
configuration path: ./compose.yaml: ./site
media/download paths: n/a
internal address/port: web:80
published address/port: DOCKER-HOST:8080
dependencies: none
health test: curl unique phrase
backup method: copy compose.yaml + site/
update procedure: change tag -> config -> pull -> up -d -> test
rollback procedure: restore compose.yaml.bak -> pull -> up -d -> test
In plain words: Make a safety copy first so a mistake does not erase your work.
Break / fix
Break / fix
In plain words: Break one thing on purpose, watch the failure, then repair it.
More detail: Change only one variable at a time.
Break/fix scenarios
Run with commands; change only one variable at a time.
- Restart loop:
docker compose ps+docker inspect --format '{{.State.ExitCode}} {{.State.Error}}' CID+ first error inlogs. - Port conflict:
Windows (CMD / PowerShell)
netstat -ano | findstr :8080
Linux / macOS (Terminal)
ss -lntp | grep 8080 || sudo lsof -i :8080
- Disk pressure:
docker system dfand hostdf -h/ PowerShellGet-PSDrive. Do not rundocker system prune --volumescasually. - Permission denied: inspect mount UID/GID and mode.
- Update regression: restore last-known-good tag from step 1.
In plain words: Compose is the recipe file that starts and stops your app group together.
Fix chart
Feedback / common mistakes
In plain words: These are the traps other students fall into. Check yourself against the list.
- Skipping evidence and calling it done.
- Changing multiple variables before retesting.
- Moving on without completing Feynman teach-back.
In plain words: Big idea: - Skipping evidence and calling it done.
Hands-on
Lab gate
In plain words: This is the hands-on part. Follow the numbered steps and keep notes of what you saw.
All boxes must be true before the next class unlocks. If you fail: feedback → targeted review → new practice → reassess.
In plain words: Big idea: All boxes must be true before the next class unlocks.
- [ ] A service contract is complete.
- [ ] Health is verified above the container-process layer.
- [ ] Configuration is backed up.
- [ ] An update and rollback are demonstrated.
- [ ] The runbook identifies last-known-good version and acceptance test.
- [ ] Logs shared as evidence contain no secrets.
- [ ] Prior-knowledge check answered
- [ ] Feynman teach-back completed (Explain, Simplify, Example, Weak spot, Retry)
- [ ] Independent practice completed
- [ ] Retrieval check attempted (target ≥80% when scored)
- [ ] Evidence recorded in workbook / verification matrix
In plain words: A health check asks “are you really ready?” not just “did the process start?”