Image naming conventions (registry/image:tag) in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the image with the official Docker Hub registry.

Docker

docker pull [1]/ubuntu:latest

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

Aregistry.hub.docker.com

Bhub.docker.com

Cdocker.io

Ddockerhub

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'dockerhub' which is not a valid registry prefix.

Using 'hub.docker.com' which is a website, not the registry name.

The official Docker Hub registry is referenced as docker.io. This prefix is optional but correct.

2fill in blank

medium

Complete the code to tag an image with a specific version.

Docker

docker tag myapp [1]/myrepo/myapp:1.0

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

Amyregistry.com:5000

Bmyregistry

Cmyregistry.com

Dmyregistry:5000

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the port number when required.

Using invalid registry names without domain format.

When specifying a registry with a custom port, include the port after a colon, like myregistry.com:5000.

3fill in blank

hard

Fix the error in the image name to correctly specify the tag.

Docker

docker pull alpine[1]latest

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

A:

B/

C_

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using slash or dash instead of colon to separate tag.

Omitting the colon causes Docker to treat 'latest' as part of the image name.

The tag is separated from the image name by a colon :, not a slash or dash.

4fill in blank

hard

Fill both blanks to create a valid image name with registry and tag.

Docker

docker push [1]/[2]:stable

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

Aregistry.example.com

Bmyapp

Cappimage

Dexample.com

Attempts:

3 left

💡 Hint

Common Mistakes

Using just 'example.com' without 'registry.' prefix if that is the registry.

Confusing image name with registry domain.

The registry is registry.example.com and the image name is appimage. The tag stable is after the colon.

5fill in blank

hard

Fill all three blanks to create a full image name with registry, repository, and tag.

Docker

docker pull [1]/[2]/[3]:v2

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

Aregistry.io

Blibrary

Cnginx

Ddockerhub

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'dockerhub' which is not a valid registry name.

Mixing up repository and image names.

The full image name includes the registry registry.io, the repository library, and the image nginx. The tag v2 specifies the version.

Practice

1. Which part of the Docker image name docker.io/library/nginx:latest specifies the version of the image?

easy

A. latest

B. docker.io

C. nginx

D. library

Solution

1. Step 1: Identify the tag in the image name

   The tag is the part after the colon (:), which specifies the version or variant of the image.

2. Step 2: Locate the tag in the example

   In docker.io/library/nginx:latest, the tag is latest.

3. Final Answer:

   latest -> Option A

4. Quick Check:

   Tag = latest [OK]

Hint: Tag is always after colon ':' in image name [OK]

Common Mistakes:

• Confusing registry with tag
• Thinking image name is the tag
• Ignoring the colon separator

2. Which of the following is the correct syntax for a Docker image name with a registry, image, and tag?

easy

A. tag/image:registry

B. registry/image:tag

C. image:tag/registry

D. image/registry:tag

Solution

1. Step 1: Recall the Docker image naming format

   The correct format is registry/image:tag, where registry is optional but comes first, then image name, then tag after colon.

2. Step 2: Match the options to the format

   Only registry/image:tag matches the correct order and separators.

3. Final Answer:

   registry/image:tag -> Option B

4. Quick Check:

   Format = registry/image:tag [OK]

Hint: Registry first, then image, then tag after ':' [OK]

Common Mistakes:

• Placing tag before image
• Swapping registry and image order
• Using wrong separators like '/' for tag

3. What is the full image name including registry and tag for the official Redis image version 7.0 from Docker Hub?

medium

A. docker.io/redis7:0

B. redis:7.0

C. redis/docker.io:7.0

D. docker.io/redis:7.0

Solution

1. Step 1: Understand Docker Hub default registry

   Docker Hub's registry is docker.io. The official images are under this registry.

2. Step 2: Compose full image name

   The full name includes registry, image name, and tag: docker.io/redis:7.0.

3. Final Answer:

   docker.io/redis:7.0 -> Option D

4. Quick Check:

   Full name = docker.io/redis:7.0 [OK]

Hint: Full name = registry/image:tag, Docker Hub registry is docker.io [OK]

Common Mistakes:

• Putting registry after image
• Missing registry for full name
• Incorrect tag format

4. You try to pull the image myregistry.com/myapp but get an error. Which of these is a likely cause?

medium

A. Missing tag defaults to 'latest', but image may not have it

B. Registry name cannot contain dots '.'

C. Image name must always include a tag

D. Registry must be 'docker.io' only

Solution

1. Step 1: Understand default tag behavior

   If no tag is given, Docker uses latest by default. If the image does not have a 'latest' tag, pull fails.

2. Step 2: Check other options for errors

   Registry names can contain dots, tags are optional, and registries can be other than docker.io.

3. Final Answer:

   Missing tag defaults to 'latest', but image may not have it -> Option A

4. Quick Check:

   Default tag 'latest' may be missing [OK]

Hint: No tag means 'latest' assumed, may cause pull failure [OK]

Common Mistakes:

• Thinking registry can't have dots
• Believing tag is mandatory
• Assuming only docker.io registry works

5. You want to tag a local image myapp to push it to a private registry at registry.example.com with version v2. Which command correctly tags the image?

hard

A. docker tag myapp:v2 registry.example.com/myapp

B. docker tag registry.example.com/myapp:v2 myapp

C. docker tag myapp registry.example.com/myapp:v2

D. docker tag myapp registry.example.com:v2/myapp

Solution

1. Step 1: Understand docker tag syntax

   The syntax is docker tag SOURCE_IMAGE[:TAG] TARGET_IMAGE[:TAG].

2. Step 2: Apply to given names

   Source is myapp (local), target is registry.example.com/myapp:v2 to specify registry and tag.

3. Final Answer:

   docker tag myapp registry.example.com/myapp:v2 -> Option C

4. Quick Check:

   Tag command: source then target with registry and tag [OK]

Hint: Tag command: source image then target with registry:tag [OK]

Common Mistakes:

• Swapping source and target images
• Placing tag in wrong position
• Using invalid registry/tag format