Building images with docker build - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to build a Docker image from the current directory.

Docker

docker build [1] .

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

A-p 8080:80

B-d

C-t myimage

D--rm

Attempts:

3 left

💡 Hint

Common Mistakes

Using -d which is for running containers, not building images.

Using -p which is for port mapping when running containers.

Using -rm which is not a valid docker build flag.

The -t flag tags the image with a name, which is required to identify the built image.

2fill in blank

medium

Complete the command to build a Docker image using a specific Dockerfile named 'Dockerfile.dev'.

Docker

docker build -f [1] .

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

ADockerfile.txt

BDockerfile.dev

Cdockerfile

DDockerfile.prod

Attempts:

3 left

💡 Hint

Common Mistakes

Using a file name that does not exist.

Using lowercase 'dockerfile' which is not the correct file name.

Using a file with wrong extension like .txt.

The -f flag specifies the Dockerfile to use. Here, the file is named Dockerfile.dev.

3fill in blank

hard

Fix the error in the command to build an image with tag 'webapp:latest'.

Docker

docker build -t [1] .

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

Awebapp_latest

Bwebapp latest

Cwebapp/latest

Dwebapp:latest

Attempts:

3 left

💡 Hint

Common Mistakes

Using a slash '/' instead of a colon ':'.

Using spaces in the tag name.

Using underscores which are allowed but not standard for tags.

The tag format is name:tag. Using a slash or space is invalid.

4fill in blank

hard

Fill both blanks to build an image with tag 'app:v1' and no cache.

Docker

docker build [1] [2] .

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

A--no-cache

B-t app:v1

C-f Dockerfile

D--rm

Attempts:

3 left

💡 Hint

Common Mistakes

Using --rm which removes intermediate containers but does not disable cache.

Using -f Dockerfile which is default and not needed here.

Reversing the order of options is allowed but can confuse beginners.

The -t flag sets the image tag, and --no-cache forces Docker to build without using cache.

5fill in blank

hard

Fill all three blanks to build an image named 'backend' with tag 'v2', using Dockerfile 'Dockerfile.prod' and no cache.

Docker

docker build [1] [2] [3] .

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

A-f Dockerfile.prod

B-t backend:v2

C--no-cache

D--pull

Attempts:

3 left

💡 Hint

Common Mistakes

Using --pull instead of --no-cache.

Omitting the Dockerfile option when a custom file is needed.

Incorrect tag format or missing tag.

Use -f to specify the Dockerfile, -t to tag the image, and --no-cache to build fresh without cache.

Practice

1. What does the docker build command do?

easy

A. It creates a Docker image from a Dockerfile and context files.

B. It runs a Docker container from an image.

C. It deletes unused Docker images.

D. It lists all running Docker containers.

Solution

1. Step 1: Understand the purpose of docker build

   The docker build command reads instructions from a Dockerfile and packages files from the build context into a new image.

2. Step 2: Differentiate from other Docker commands

   Running containers, deleting images, or listing containers are done by other commands like docker run, docker rmi, and docker ps.

3. Final Answer:

   It creates a Docker image from a Dockerfile and context files. -> Option A

4. Quick Check:

   docker build = create image [OK]

Hint: Remember: build = create image from Dockerfile [OK]

Common Mistakes:

• Confusing build with run command
• Thinking build deletes images
• Mixing build with container listing

2. Which of the following is the correct syntax to build a Docker image named myapp from the current directory?

easy

A. docker build . -name myapp

B. docker build myapp -t .

C. docker build -t myapp .

D. docker build --image myapp .

Solution

1. Step 1: Identify the correct order and options for docker build

   The correct syntax uses -t to tag the image name, followed by the build context (here, current directory .).

2. Step 2: Check each option for syntax correctness

   docker build -t myapp . correctly places -t myapp before the context .. Options A, B, and D misuse flags or order.

3. Final Answer:

   docker build -t myapp . -> Option C

4. Quick Check:

   docker build -t name context [OK]

Hint: Use -t before context folder to name image [OK]

Common Mistakes:

• Placing image name after context
• Using wrong flags like --image or -name
• Omitting the build context folder

3. Given this Dockerfile in the current directory:

FROM alpine
RUN echo "Hello Docker" > /hello.txt

What will be the output of docker build -t testimage . if successful?

medium

A. An image named testimage is created with a file /hello.txt containing 'Hello Docker'.

B. A container runs and prints 'Hello Docker' to the terminal.

C. The build fails because echo is not a valid Docker command.

D. An image is created but /hello.txt is empty.

Solution

1. Step 1: Understand Dockerfile instructions

   FROM alpine sets base image; RUN echo "Hello Docker" > /hello.txt creates a file inside the image.

2. Step 2: Interpret the build command output

   The build creates an image named testimage with the file /hello.txt containing the text 'Hello Docker'. No container runs or prints output during build.

3. Final Answer:

   An image named testimage is created with a file /hello.txt containing 'Hello Docker'. -> Option A

4. Quick Check:

   RUN creates files in image, no output printed [OK]

Hint: RUN commands modify image, they don't print output during build [OK]

Common Mistakes:

• Thinking RUN prints to terminal during build
• Confusing image creation with container run
• Assuming build fails due to shell commands

4. You run docker build -t myapp . but get the error: failed to read dockerfile: open Dockerfile: no such file or directory. What is the most likely cause?

medium

A. The build context folder is empty.

B. The -t option is used incorrectly.

C. Docker daemon is not running.

D. The Dockerfile is missing from the current directory.

Solution

1. Step 1: Analyze the error message

   The error says Docker cannot find the Dockerfile in the build context folder (current directory).

2. Step 2: Identify the cause

   If the Dockerfile is missing, Docker cannot build the image. The -t option and daemon status do not cause this specific error.

3. Final Answer:

   The Dockerfile is missing from the current directory. -> Option D

4. Quick Check:

   Missing Dockerfile = build fails with file not found [OK]

Hint: Check Dockerfile exists in build folder if build fails [OK]

Common Mistakes:

• Assuming wrong flag causes error
• Not verifying Dockerfile presence
• Ignoring daemon status for this error

5. You want to build a Docker image named webapp:v1 using a Dockerfile located in ./app folder, but your current directory is the parent folder. Which command correctly builds the image?

hard

A. docker build -t webapp:v1 ./app

B. docker build -t webapp:v1 -f ./app/Dockerfile ./app

C. docker build ./app -t webapp:v1

D. docker build -f app/Dockerfile -t webapp:v1 ./app

Solution

1. Step 1: Understand build context and Dockerfile location

   The build context is the folder with the Dockerfile and files needed. Here, it's ./app.

2. Step 2: Choose correct command syntax

   docker build -t webapp:v1 -f ./app/Dockerfile ./app uses -t webapp:v1 to tag, -f ./app/Dockerfile to specify Dockerfile path, and ./app as context, which is correct. docker build -t webapp:v1 ./app assumes Dockerfile is in context folder but does not specify path explicitly. docker build ./app -t webapp:v1 has wrong order. docker build -f app/Dockerfile -t webapp:v1 ./app has incomplete Dockerfile path.

3. Final Answer:

   docker build -t webapp:v1 -f ./app/Dockerfile ./app -> Option B

4. Quick Check:

   Tag with -t, specify Dockerfile with -f, context last [OK]

Hint: Tag with -t, specify Dockerfile path with -f, context last [OK]

Common Mistakes:

• Wrong order of options and context
• Incorrect Dockerfile path with -f
• Using current folder when Dockerfile is elsewhere