Why images are blueprints for containers in Docker - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the command to list all Docker images on your system.

Docker

docker [1]

Drag options to blanks, or click blank then click option'

Astart

Brun

Cbuild

Dimages

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'docker run' instead of 'docker images' to list images.

The docker images command shows all images stored locally. Images are the blueprints for containers.

2fill in blank

medium

Complete the command to create a container from an image named 'nginx'.

Docker

docker [1] nginx

Drag options to blanks, or click blank then click option'

Arun

Bimages

Cbuild

Dpull

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'docker build' instead of 'docker run' to start a container.

The docker run command creates and starts a container from an image.

3fill in blank

hard

Fix the error in this Dockerfile line to set the base image to Ubuntu.

Docker

FROM [1]

Drag options to blanks, or click blank then click option'

Aubuntu:latest

Bnginx

Ccontainer

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' or 'container' instead of a valid image name after FROM.

The FROM instruction sets the base image. ubuntu:latest is the correct image name.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps each container name to its status if the status is 'running'.

Docker

{container['[1]']: container['[2]'] for container in containers if container['status'] == 'running'}

Drag options to blanks, or click blank then click option'

Aname

Bstatus

Cid

Dimage

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'id' or 'image' instead of 'name' or 'status'.

We use 'name' as the key and 'status' as the value to map container names to their statuses.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps each image's tag to its size if the size is greater than 100MB.

Docker

{image['[1]']: image['[2]'] for image in images if image['[3]'] > 100}

Drag options to blanks, or click blank then click option'

Aid

Bsize

Ctag

Dcreated

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'id' or 'created' instead of 'tag' or 'size'.

The key is the image 'tag', the value is 'size', and the condition checks if 'size' is greater than 100MB.

Practice

1. What is the main role of a Docker image in container technology?

easy

A. It acts as a blueprint containing all setup details to create containers.

B. It runs the container directly without any changes.

C. It stores data generated by running containers.

D. It manages network connections between containers.

Solution

1. Step 1: Understand what an image contains

   A Docker image includes all files, settings, and instructions needed to build a container.

2. Step 2: Compare image and container roles

   Containers are created from images, similar to how buildings are made from blueprints.

3. Final Answer:

   It acts as a blueprint containing all setup details to create containers. -> Option A

4. Quick Check:

   Image = Blueprint for containers [OK]

Hint: Images hold setup info; containers are running instances [OK]

Common Mistakes:

• Confusing images with running containers
• Thinking images store container data
• Believing images manage container networking

2. Which of the following is the correct Docker command to create a container from an image named myapp?

easy

A. docker build myapp

B. docker create-image myapp

C. docker run myapp

D. docker start myapp

Solution

1. Step 1: Identify command to create and start container

   The docker run command creates and starts a container from an image.

2. Step 2: Check other commands

   docker build creates an image, not a container. docker create-image is invalid. docker start starts an existing container, not create one.

3. Final Answer:

   docker run myapp -> Option C

4. Quick Check:

   Run = create and start container [OK]

Hint: Use 'docker run' to create and start containers [OK]

Common Mistakes:

• Using 'docker build' to create containers
• Confusing 'docker start' with container creation
• Using non-existent commands like 'docker create-image'

3. Given the Dockerfile below, what will the resulting image contain?

FROM alpine:latest
RUN echo "Hello World" > /greeting.txt

medium

A. An empty Alpine image without any new files.

B. An Alpine Linux image with a file /greeting.txt containing 'Hello World'.

C. An image that automatically runs 'echo' when started.

D. A container running Alpine Linux printing 'Hello World' on start.

Solution

1. Step 1: Analyze Dockerfile instructions

   The FROM alpine:latest sets base image. The RUN command creates a file /greeting.txt with 'Hello World'.

2. Step 2: Understand image content

   The image will include Alpine Linux plus the new file created during build.

3. Final Answer:

   An Alpine Linux image with a file /greeting.txt containing 'Hello World'. -> Option B

4. Quick Check:

   RUN adds files to image layers [OK]

Hint: RUN commands add files to image layers [OK]

Common Mistakes:

• Thinking RUN commands run on container start
• Confusing image content with container runtime behavior
• Assuming files are created only when container runs

4. You tried to create a container with docker run myapp but got an error: Unable to find image 'myapp' locally. What is the likely cause?

medium

A. The command syntax is incorrect; 'docker run' needs extra flags.

B. The container is already running with the name 'myapp'.

C. Docker daemon is not running on your system.

D. The image 'myapp' does not exist locally or on Docker Hub.

Solution

1. Step 1: Understand the error message

   The error says Docker cannot find the image named 'myapp' locally.

2. Step 2: Check image availability

   If the image is not on your machine and not on Docker Hub, Docker cannot create the container.

3. Final Answer:

   The image 'myapp' does not exist locally or on Docker Hub. -> Option D

4. Quick Check:

   Image missing causes 'unable to find image' error [OK]

Hint: Check if image exists locally or on Docker Hub [OK]

Common Mistakes:

• Assuming container name conflicts cause this error
• Ignoring Docker daemon status
• Thinking command syntax is wrong without flags

5. You want to ensure your app runs exactly the same on any machine. Which Docker concept helps achieve this by using a reusable setup?

hard

A. Docker images as blueprints for containers

B. Docker volumes for persistent data

C. Docker networks for container communication

D. Docker logs for monitoring container output

Solution

1. Step 1: Identify the concept for consistent app setup

   Docker images contain all setup details, ensuring the app environment is the same everywhere.

2. Step 2: Compare other options

   Volumes store data, networks connect containers, logs record output; none guarantee identical app setup.

3. Final Answer:

   Docker images as blueprints for containers -> Option A

4. Quick Check:

   Images ensure consistent app environment [OK]

Hint: Use images to keep app setup consistent everywhere [OK]

Common Mistakes:

• Confusing volumes with environment consistency
• Thinking networks control app setup
• Believing logs affect app environment