[LAB]

week-01/labs/lab-04-lifecycle-investigation/WORKSHEET.md

week-01/labs/lab-04-lifecycle-investigation/WORKSHEET.md

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Course Contents 8 weeks · 45 labs

Container Lifecycle Investigation

Time: 30-45 minutes
Type: Independent exploration
Deliverable: This completed worksheet with your answers

Instructions

You've run containers in Lab 1 and Lab 2. Now it's time to really understand how the container lifecycle works.

Rules:

  1. Answer each question by running commands and observing the results
  2. Write your answers in your own words (no copy-paste from docs)
  3. Include the commands you ran to discover the answer
  4. Mark any surprises or "aha!" moments with 💡

You'll learn more from being wrong and figuring out why than from being right immediately.

Part 1: Understanding Container States

Question 1.1: Stop vs Start vs Restart

Start an nginx container, then stop it, then start it again.

Question: Did you use the same container or create a new one? How can you tell?

Commands I ran:

# Your commands here

My answer:

💡 Aha moment (if any):

Question 1.2: Stop vs Kill

Question: What's the difference between docker stop and docker kill?

Experiment:

  • Run two nginx containers
  • docker stop one
  • docker kill the other
  • Check their exit codes

Commands I ran:

# Your commands here

My answer:

Exit codes I observed:

Question 1.3: Created But Not Running

Question: Create a container but don't start it (hint: docker create). What state is it in? Can you exec into it? Why or why not?

Commands I ran:

# Your commands here

My answer:

Question 1.4: Paused Containers

Question: Pause a running nginx container. Can you still see it in docker ps? What happens if you try to curl it? What about docker exec?

Commands I ran:

# Your commands here

My answer:

What worked / what didn't:

Part 2: Data Lifecycle

Question 2.1: Survived Stop?

Experiment:

  1. Start nginx
  2. Exec in and create a file: echo "test" > /tmp/myfile.txt
  3. Stop the container
  4. Start it again
  5. Exec in and check if the file exists

Question: Is the file still there after stop/start? Why or why not?

Commands I ran:

# Your commands here

My answer:

Question 2.2: Survived Remove?

Experiment:

  1. Start nginx
  2. Exec in and create a file: echo "test" > /tmp/myfile.txt
  3. Stop the container
  4. Remove the container (docker rm)
  5. Start a new container from the same image
  6. Check if the file exists

Question: Is the file still there after rm + new container? Why or why not?

Commands I ran:

# Your commands here

My answer:

💡 What does this tell you about the difference between containers and images?

Question 2.3: Crashed Container Logs

Experiment:
Run a container that crashes immediately:

docker run --name crasher nginx /bin/false

Questions:

  • What state is the container in?
  • Can you still get its logs?
  • Can you restart it?

Commands I ran:

# Your commands here

My answers:

Part 3: Lifecycle Commands

Question 3.1: Restart Running Container

Question: What happens if you docker restart a container that's already running? Does it get a new container ID?

Commands I ran:

# Your commands here

My answer:

Question 3.2: Renaming Containers

Questions:

  • Can you rename a running container?
  • Can you rename a stopped container?
  • If you start a container without --name, can you still rename it?

Commands I ran:

# Your commands here

My answers:

Question 3.3: The --rm Flag Mystery

Experiment:

  1. Start a container with the --rm flag
  2. Stop it
  3. Try to find it with docker ps -a

Question: Where did it go? When is --rm useful?

Commands I ran:

# Your commands here

My answer:

Part 4: The Image-Container Relationship

Question 4.1: Deleting Images

Experiment:

  1. Run 2 containers from nginx (let them keep running)
  2. Try to delete the nginx image

Question: What happens? Why?

Commands I ran:

# Your commands here

My answer:

Now stop and remove all containers, then try deleting the image. What happens?

Question 4.2: Container Independence

Experiment:

  1. Run 3 nginx containers from the same image
  2. Exec into container 1 and create /tmp/file1.txt
  3. Exec into container 2 and create /tmp/file2.txt
  4. Exec into container 3 and check what files exist in /tmp/

Question: Can container 3 see file1.txt and file2.txt? Why or why not?

Commands I ran:

# Your commands here

My answer:

💡 What does this tell you about container isolation?

Question 4.3: Image Immutability

Experiment:

  1. Run nginx
  2. Exec in and modify /usr/share/nginx/html/index.html
  3. Stop and remove the container
  4. Run a new nginx container
  5. Check if your modifications are still there

Question: Are your changes in the new container? What happened to them?

Commands I ran:

# Your commands here

My answer:

How would you make permanent changes to an image?

Part 5: Real-World Debugging Scenario

Question 5.1: The Crashing Container

Scenario: You deployed a container in production. It crashes every 30 seconds (exits with code 1). You need to debug it, but it keeps restarting before you can exec in.

Experiment:
Simulate this with:

docker run -d --name broken --restart always nginx /bin/false

Watch it crash and restart. Now try to exec into it.

Question: How do you keep it alive long enough to investigate? (Try at least 2 different approaches)

Commands I tried:

# Your experiments here

My solution(s):

💡 Which approach would you use in production and why?

Question 5.2: Container Resource Detective

Experiment:

  1. Run an nginx container
  2. Use docker stats to see its resource usage
  3. Use docker inspect to see its configuration

Questions:

  • How much memory is it using right now?
  • What's its IP address?
  • What ports are exposed?
  • What's its restart policy?

Commands I ran:

# Your commands here

My answers:

Part 6: Lifecycle Troubleshooting

Question 6.1: Port Already in Use

Experiment:

  1. Start nginx on port 8080
  2. Try to start another nginx on port 8080

Question: What error do you get? How would you find what's using port 8080 if you didn't know?

Commands I ran:

# Your commands here

My answer:

How to fix it:

Question 6.2: Container Name Conflicts

Experiment:

  1. Run a container named "test"
  2. Stop it (don't remove)
  3. Try to run another container named "test"

Question: What happens? How do you fix it?

Commands I ran:

# Your commands here

My answer:

Question 6.3: Finding Lost Containers

Scenario: You ran several containers yesterday during testing. Some are stopped, some are running. You can't remember their names.

Questions:

  • How do you find ALL containers (running and stopped)?
  • How do you find just the stopped ones?
  • How do you remove all stopped containers at once?

Commands I ran:

# Your commands here

My answers:

Final Reflection

What surprised you most about container lifecycle?

My answer:

What's one thing you'll do differently now when working with containers?

My answer:

If you had to explain the difference between an image and a container to someone new, how would you explain it?

My answer:

Cleanup

Before submitting, clean up your test containers:

docker stop $(docker ps -aq)
docker rm $(docker ps -aq)
docker system prune -f

Submission

Save this file as YOURNAME-lifecycle-investigation.md and submit according to your instructor's directions.

Bonus Challenges (Optional)

If you finish early:

  1. The Zombie Hunter: What's the difference between docker ps and docker ps -a? Why would stopped containers stick around?

  2. The Network Detective: Two containers running on the same host. Can they talk to each other? How?

  3. The Volume Mystery: Create a container with -v /data. Put a file in /data. Remove the container. Where did the file go?