Starting and stopping containers in Docker - Mini Project: Build & Apply

Starting and stopping containers

📖 Scenario: You are managing a small web application using Docker containers. You need to start and stop containers to control the app's availability.

🎯 Goal: Learn how to start and stop Docker containers using commands.

📋 What You'll Learn

Use the exact container name mywebapp

Start the container using the correct Docker command

Stop the container using the correct Docker command

Check the container status using Docker commands

💡 Why This Matters

🌍 Real World

Starting and stopping containers is a daily task for managing applications in Docker environments. It helps control app availability and resource use.

💼 Career

DevOps engineers and system administrators frequently start and stop containers to deploy updates, troubleshoot, or scale applications.

1

Create and run a container named mywebapp

Run a Docker container named mywebapp using the nginx image in detached mode.

Docker

# Run the container named mywebapp
# Your code here

Hint

Use docker run -d --name mywebapp nginx to start the container in the background.

2

Check if the container mywebapp is running

Use the Docker command to list running containers and check for mywebapp.

Docker

docker run -d --name mywebapp nginx
# List running containers to check mywebapp
# Your code here

Hint

Use docker ps --filter "name=mywebapp" to see if the container is running.

3

Stop the container named mywebapp

Use the Docker command to stop the container named mywebapp.

Docker

docker run -d --name mywebapp nginx
docker ps --filter "name=mywebapp"
# Stop the container mywebapp
# Your code here

Hint

Use docker stop mywebapp to stop the container.

4

Verify the container mywebapp is stopped

List all containers including stopped ones and check that mywebapp is not running.

Docker

docker run -d --name mywebapp nginx
docker ps --filter "name=mywebapp"
docker stop mywebapp
# List all containers to verify mywebapp is stopped
# Your code here

Hint

Use docker ps -a --filter "name=mywebapp" to see the container status including stopped ones.

Practice

1. Which command is used to start a container that has been stopped in Docker?

easy

A. docker run <container_name>

B. docker stop <container_name>

C. docker start <container_name>

D. docker restart <container_name>

Solution

1. Step 1: Understand the purpose of docker start

   This command resumes a container that was previously stopped without creating a new one.

2. Step 2: Differentiate from other commands

   docker run creates a new container, docker stop stops a running container, and docker restart stops then starts a container.

3. Final Answer:

   docker start <container_name> -> Option C

4. Quick Check:

   Start stopped container = docker start [OK]

Hint: Use 'docker start' to resume stopped containers fast [OK]

Common Mistakes:

• Confusing 'docker run' with 'docker start'
• Using 'docker stop' to start containers
• Thinking 'docker restart' only starts containers

2. Which of the following is the correct syntax to stop a running Docker container named webapp?

easy

A. docker terminate webapp

B. docker kill webapp

C. docker pause webapp

D. docker stop webapp

Solution

1. Step 1: Identify the command to safely stop a container

   docker stop sends a signal to gracefully stop the container.

2. Step 2: Check other options

   docker kill forcefully stops, docker pause suspends, and docker terminate is invalid.

3. Final Answer:

   docker stop webapp -> Option D

4. Quick Check:

   Stop container safely = docker stop [OK]

Hint: Use 'docker stop' to safely end container processes [OK]

Common Mistakes:

• Using 'docker kill' instead of 'docker stop'
• Confusing 'docker pause' with stopping
• Using non-existent commands like 'docker terminate'

3. What will be the output of the following commands if the container db is currently stopped?

docker start db
docker stop db

medium

A. Container 'db' starts, then stops successfully

B. Error: container 'db' not found

C. Container 'db' remains stopped

D. Container 'db' restarts automatically

Solution

1. Step 1: Analyze docker start db

   This command starts the stopped container named 'db'.

2. Step 2: Analyze docker stop db

   This command stops the running container 'db' safely.

3. Final Answer:

   Container 'db' starts, then stops successfully -> Option A

4. Quick Check:

   Start then stop container = success [OK]

Hint: Start then stop a container runs commands without error [OK]

Common Mistakes:

• Assuming 'docker start' creates a new container
• Expecting errors if container exists
• Thinking container restarts automatically without command

4. You run docker start myapp but get the error: Error response from daemon: No such container: myapp. What is the most likely cause?

medium

A. Docker daemon is not running

B. The container 'myapp' does not exist

C. You need to use docker run instead

D. The container 'myapp' is already running

Solution

1. Step 1: Understand the error message

   The error says 'No such container', meaning 'myapp' is not found in Docker's container list.

2. Step 2: Check other options

   If it was running, 'docker start' would not error; 'docker run' creates new containers but error is about missing container; daemon not running causes different errors.

3. Final Answer:

   The container 'myapp' does not exist -> Option B

4. Quick Check:

   No such container error = container missing [OK]

Hint: Check container existence before starting [OK]

Common Mistakes:

• Assuming container is running when error says missing
• Trying 'docker run' without checking container list
• Ignoring Docker daemon status

5. You want to stop a container named api-server but ensure it has 10 seconds to finish its work before stopping. Which command should you use?

hard

A. docker stop -t 10 api-server

B. docker kill -t 10 api-server

C. docker pause api-server

D. docker stop api-server -timeout 10

Solution

1. Step 1: Understand the timeout option in docker stop

   The -t or --time flag sets seconds to wait before killing the container.

2. Step 2: Evaluate the options

   docker kill does not support -t, docker pause only suspends, and -timeout is invalid syntax.

3. Final Answer:

   docker stop -t 10 api-server -> Option A

4. Quick Check:

   Stop with timeout = docker stop -t [OK]

Hint: Use 'docker stop -t seconds' to allow graceful shutdown [OK]

Common Mistakes:

• Using 'docker kill' with timeout flag
• Using invalid flags like '-timeout'
• Confusing 'pause' with stopping