Tagging images during build in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to tag the Docker image as 'myapp:latest' during build.

Docker

docker build -t myapp[1] .

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

A-latest

B:latest

C latest

D/latest

Attempts:

3 left

💡 Hint

Common Mistakes

Using a dash instead of a colon to separate the tag

Adding a space before the tag

Using a slash instead of a colon

The -t option tags the image. The tag is added after a colon : without spaces.

2fill in blank

medium

Complete the command to tag the image with a version number 'v1.0' during build.

Docker

docker build -t myapp[1] .

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

A:v1.0

B v1.0

C-v1.0

D/v1.0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a dash instead of a colon

Adding spaces before the tag

Using a slash instead of a colon

The version tag is added after the image name with a colon and no spaces.

3fill in blank

hard

Fix the error in the command to tag the image as 'myapp:prod'.

Docker

docker build -t myapp[1] .

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

A prod

B/prod

C:prod

D-prod

Attempts:

3 left

💡 Hint

Common Mistakes

Adding a space before the tag

Using a dash or slash instead of a colon

The correct tag separator is a colon : with no spaces.

4fill in blank

hard

Complete the code to tag the image as 'myapp' with version '2.1' during build.

Docker

docker build -t myapp:[1] .

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

A:

B-

C2.1

Dv2.1

Attempts:

3 left

💡 Hint

Common Mistakes

Using a dash instead of colon

Adding 'v' before the version number when not required

The tag separator is a colon, followed by the version number without extra characters.

5fill in blank

hard

Fill both blanks to tag the 'myapp' image with version '3.0' to 'myrepo/myapp:3.0'.

Docker

docker tag myapp:[1] myrepo/myapp[2]

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

A:

B3.0

C:3.0

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using slash instead of colon for tags

Including the version tag without colon

Mixing separators between source and target

The tag separator is a colon before the version number in both source and target image names.

Practice

1. What is the purpose of using the -t option in the docker build command?

easy

A. To assign a name and tag to the image during build

B. To specify the Dockerfile location

C. To run the container after building the image

D. To remove intermediate containers after build

Solution

1. Step 1: Understand the docker build command options

   The -t option is used to tag the image with a name and optionally a tag.

2. Step 2: Identify the purpose of tagging

   Tagging helps to identify and manage images easily by giving them a readable name and version.

3. Final Answer:

   To assign a name and tag to the image during build -> Option A

4. Quick Check:

   -t tags image [OK]

Hint: Remember: -t means tag your image name during build [OK]

Common Mistakes:

• Confusing -t with specifying Dockerfile path
• Thinking -t runs the container
• Assuming -t deletes containers

2. Which of the following is the correct syntax to build a Docker image named myapp with tag v1 from the current directory?

easy

A. docker build -t myapp:v1 .

B. docker build myapp:v1 .

C. docker build -name myapp:v1 .

D. docker build --tag=myapp v1 .

Solution

1. Step 1: Recall the correct docker build syntax for tagging

   The correct syntax uses -t name:tag followed by the build context (here, .).

2. Step 2: Match the options with correct syntax

   docker build -t myapp:v1 . matches the correct syntax: docker build -t myapp:v1 .

3. Final Answer:

   docker build -t myapp:v1 . -> Option A

4. Quick Check:

   docker build -t name:tag . [OK]

Hint: Use -t before name:tag and end with build context [OK]

Common Mistakes:

• Omitting -t option
• Using incorrect flags like -name
• Placing tag after context

3. What will be the output of the command docker images after running docker build -t testapp:latest . successfully?

medium

A. An error message about missing tag

B. No new images listed

C. A container named testapp running

D. An image named testapp with tag latest listed

Solution

1. Step 1: Understand what docker build -t testapp:latest . does

   This command builds an image and tags it as testapp:latest.

2. Step 2: Check what docker images shows

   The docker images command lists all images including the newly built one with its name and tag.

3. Final Answer:

   An image named testapp with tag latest listed -> Option D

4. Quick Check:

   Build tags appear in docker images [OK]

Hint: Built images show up with their tags in docker images list [OK]

Common Mistakes:

• Expecting containers to appear in images list
• Thinking build fails without explicit tag
• Confusing image and container outputs

4. You run docker build -t myimage: . but get an error saying "invalid reference format". What is the most likely cause?

medium

A. The build context path is incorrect

B. The Dockerfile is missing in the directory

C. The tag name is missing a tag part after colon

D. The image name contains uppercase letters

Solution

1. Step 1: Analyze the error message "invalid reference format"

   This error usually means the image name or tag format is wrong.

2. Step 2: Check the command docker build -t myimage: .

   myimage: has a colon but no tag after it, causing the "invalid reference format" error.

3. Step 3: Identify the most common cause

   The most common cause is a missing tag after colon in the tag name, causing invalid format.

4. Final Answer:

   The tag name is missing a tag part after colon -> Option C

5. Quick Check:

   Tag must be after colon, else invalid format error [OK]

Hint: Check for colon without tag in image name [OK]

Common Mistakes:

• Assuming missing Dockerfile causes this error
• Confusing build context errors with tag format
• Thinking uppercase letters cause invalid format

5. You want to build a Docker image from a Dockerfile in ./app directory and tag it with two tags: myapp:1.0 and myapp:latest. Which command correctly does this in one build?

hard

A. docker build -t myapp:1.0 ./app && docker tag myapp:1.0 myapp:latest

B. docker build -t myapp:1.0 -t myapp:latest ./app

C. docker build --tag myapp:1.0 ./app && docker build --tag myapp:latest ./app

D. docker build -t myapp:1.0:latest ./app

Solution

1. Step 1: Understand how to tag multiple tags in one build

   Docker allows multiple -t options in one build command to assign multiple tags.

2. Step 2: Analyze the options

   docker build -t myapp:1.0 -t myapp:latest ./app uses two -t flags in one command, which is correct. docker build -t myapp:1.0 ./app && docker tag myapp:1.0 myapp:latest uses two commands, which works but is two steps, not one. docker build --tag myapp:1.0 ./app && docker build --tag myapp:latest ./app runs two builds, inefficient. docker build -t myapp:1.0:latest ./app uses invalid tag format.

3. Final Answer:

   docker build -t myapp:1.0 -t myapp:latest ./app -> Option B

4. Quick Check:

   Use multiple -t flags to tag once [OK]

Hint: Use multiple -t flags in one build command [OK]

Common Mistakes:

• Trying to combine tags with colon in one string
• Running multiple builds instead of tagging once
• Using incorrect flag names like --tag