docker compose up and down - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of docker compose up when the service is already running?

You run docker compose up on a project where the containers are already running. What will happen?

A Docker Compose will attach to the existing containers and show their logs.

B Docker Compose will recreate all containers regardless of their current state.

C Docker Compose will throw an error saying containers are already running.

D Docker Compose will stop the running containers and start new ones.

💡 Hint

Think about how Docker Compose behaves to avoid restarting containers unnecessarily.

When you run docker compose up and containers are already running, Docker Compose attaches to them and streams their logs instead of recreating or stopping them.

💻 Command Output

intermediate

What happens when you run docker compose down?

You have a Docker Compose project running. You execute docker compose down. What is the result?

A It removes only the containers but leaves networks and volumes running.

B It only stops the containers but keeps networks and volumes intact.

C It stops and removes containers and networks created by <code>up</code>.

D It restarts the containers without removing anything.

💡 Hint

Consider what down means compared to stop.

docker compose down stops and removes containers and networks created by up. It cleans up the environment.

🔀 Workflow

advanced

Order the steps to safely update a service using Docker Compose

You want to update a service defined in your Docker Compose file. Put these commands in the correct order to update the service without downtime.

A 3,1,4,2

B 1,2,4,3

C 1,2,4

D 1,2

💡 Hint

Think about updating only the service without stopping the whole project.

To update a service without downtime, first pull the latest image, then rebuild and restart only that service with docker compose up -d --no-deps --build <service_name>. You do not need to bring the whole project down.

❓ Troubleshoot

advanced

Why does docker compose down not remove volumes by default?

You ran docker compose down but noticed your volumes still exist. Why does this happen?

A Volumes are persistent by design and must be removed explicitly with <code>--volumes</code> flag.

B Docker Compose has a bug that prevents volume removal.

C Volumes are removed only if containers are stopped manually before running <code>down</code>.

D Volumes are removed only if you use <code>docker compose stop</code> before <code>down</code>.

💡 Hint

Think about data safety and persistence in Docker volumes.

Docker volumes store data persistently. To avoid accidental data loss, docker compose down does not remove volumes unless you add the --volumes flag explicitly.

✅ Best Practice

expert

Which command sequence is best to completely reset a Docker Compose environment including volumes?

You want to completely reset your Docker Compose environment, removing containers, networks, and volumes. Which command sequence achieves this safely?

A docker compose down --volumes && docker network prune

B docker compose down --rmi all --volumes

C docker compose down && docker volume prune

D docker compose stop && docker compose rm -v && docker network prune

💡 Hint

Consider removing images, volumes, and networks in one command.

docker compose down --rmi all --volumes stops and removes containers, networks, volumes, and images created by the compose project, fully resetting the environment.

Practice

1. What does the command docker compose up do in a multi-container application?

easy

A. Deletes the docker-compose file

B. Stops and removes all containers

C. Starts all the containers defined in the docker-compose file

D. Builds images but does not start containers

Solution

1. Step 1: Understand the purpose of docker compose up

   This command reads the docker-compose.yml file and starts all the containers defined in it.

2. Step 2: Compare with other commands

   docker compose down stops and removes containers, so it is not the same as up.

3. Final Answer:

   Starts all the containers defined in the docker-compose file -> Option C

4. Quick Check:

   docker compose up = start containers [OK]

Hint: Remember: 'up' means start containers [OK]

Common Mistakes:

• Confusing 'up' with 'down'
• Thinking 'up' deletes files
• Assuming 'up' only builds images

2. Which of the following is the correct command to stop and remove all containers started by docker compose?

easy

A. docker compose stop

B. docker compose down

C. docker compose remove

D. docker compose kill

Solution

1. Step 1: Identify the command to stop and remove containers

   docker compose down stops and removes containers, networks, and default volumes created by up.

2. Step 2: Differentiate from other commands

   docker compose stop only stops containers but does not remove them. remove is not a valid command here.

3. Final Answer:

   docker compose down -> Option B

4. Quick Check:

   down = stop and remove [OK]

Hint: Use 'down' to stop and clean containers [OK]

Common Mistakes:

• Using 'stop' which doesn't remove containers
• Trying non-existent commands like 'remove'
• Confusing 'kill' with 'down'

3. Given this sequence of commands:
docker compose up -d
docker compose down
What will be the state of the containers after these commands?

medium

A. Containers are removed and not running

B. Containers are stopped but still exist

C. Containers are running in detached mode

D. Containers are paused

Solution

1. Step 1: Analyze docker compose up -d

   This starts containers in detached mode (running in background).

2. Step 2: Analyze docker compose down

   This stops and removes all containers started by up.

3. Final Answer:

   Containers are removed and not running -> Option A

4. Quick Check:

   up -d starts, down removes [OK]

Hint: 'down' removes containers even if started detached [OK]

Common Mistakes:

• Thinking containers remain stopped but not removed
• Confusing paused with stopped
• Assuming detached means containers stay after down

4. You ran docker compose down but your containers are still running. What is the most likely reason?

medium

A. You ran docker compose down in a different directory than the compose file

B. You forgot to add -d flag

C. The containers were started with docker run instead

D. Docker daemon is not running

Solution

1. Step 1: Understand how docker compose down works

   This command affects containers defined in the compose file in the current directory.

2. Step 2: Identify why containers remain running

   If run in a different directory, it won't find or stop those containers.

3. Final Answer:

   You ran docker compose down in a different directory than the compose file -> Option A

4. Quick Check:

   Correct directory needed for down [OK]

Hint: Run commands where your compose file is located [OK]

Common Mistakes:

• Thinking -d flag affects stopping containers
• Assuming down stops containers from docker run
• Not checking Docker daemon status

5. You want to restart your multi-container app with fresh containers, removing old volumes and networks. Which command should you run?

hard

A. docker compose up --build

B. docker compose stop && docker compose start

C. docker compose restart

D. docker compose down -v && docker compose up -d

Solution

1. Step 1: Understand the need to remove old volumes and networks

   Removing volumes requires the -v flag with docker compose down.

2. Step 2: Combine commands to remove and start fresh

   docker compose down -v removes containers, networks, and volumes; docker compose up -d starts fresh containers in detached mode.

3. Final Answer:

   docker compose down -v && docker compose up -d -> Option D

4. Quick Check:

   Use down -v to remove volumes before up [OK]

Hint: Use 'down -v' to remove volumes before 'up' [OK]

Common Mistakes:

• Using 'restart' which doesn't remove volumes
• Using 'stop' and 'start' which keep old volumes
• Assuming '--build' removes volumes