Content trust and image signing in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to enable Docker content trust.

Docker

export DOCKER_CONTENT_TRUST=[1]

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

Atrue

Bfalse

Cenabled

Don

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'false' disables content trust, so images won't be verified.

Using 'enabled' or 'on' are not valid values for this environment variable.

Setting DOCKER_CONTENT_TRUST to true enables Docker content trust, which ensures image signing and verification.

2fill in blank

medium

Complete the command to sign a Docker image named 'myapp' with tag 'v1'.

Docker

docker trust sign [1]:v1

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

Amyapp

Bappimage

Cmyimage

Dv1

Attempts:

3 left

💡 Hint

Common Mistakes

Using the tag 'v1' as the image name causes an error.

Using a wrong image name will fail to find the image to sign.

The image name is 'myapp', so the command signs 'myapp:v1'.

3fill in blank

hard

Fix the error in the command to verify a signed image 'backend:latest'.

Docker

docker trust [1] backend:latest

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

Ashow

Bcheck

Cinspect

Dverify

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'verify' causes a command not found error.

Using 'inspect' or 'show' does not check signatures.

The correct subcommand to verify a signed image is check. Other options are invalid for this purpose.

4fill in blank

hard

Fill both blanks to create a Docker trust policy file that requires signed images for the repository 'myrepo'.

Docker

{
  "[1]": {
    "myrepo": {
      "[2]": "signed"
    }
  }
}

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

Atrust_policies

Brepositories

Cpolicy

Drequire

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'trust_policies' instead of 'repositories' breaks the structure.

Using 'policy' instead of 'require' does not enforce signing.

The JSON policy uses the key repositories to list repos, and require to enforce signed images.

5fill in blank

hard

Fill all three blanks to list signed tags of the image 'frontend' in the Docker trust system.

Docker

docker trust [1] [2] --[3]

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

Ashow

Bfrontend

Cpretty

Dlist

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'show' instead of 'list' does not list signed tags.

Omitting '--pretty' shows raw output which is harder to read.

The command docker trust list frontend --pretty lists signed tags in a readable format.

Practice

1. What is the main purpose of Docker content trust?

easy

A. To speed up Docker image downloads

B. To verify the authenticity and integrity of Docker images

C. To compress Docker images for storage

D. To automatically update Docker images

Solution

1. Step 1: Understand content trust concept

   Content trust in Docker is designed to ensure images are verified and safe to use by checking their signatures.

2. Step 2: Identify the purpose from options

   Only To verify the authenticity and integrity of Docker images mentions verifying authenticity and integrity, which matches content trust's goal.

3. Final Answer:

   To verify the authenticity and integrity of Docker images -> Option B

4. Quick Check:

   Content trust = verify image authenticity [OK]

Hint: Content trust means verifying image signatures before use [OK]

Common Mistakes:

• Confusing content trust with image compression
• Thinking content trust speeds up downloads
• Assuming content trust auto-updates images

2. Which command correctly enables Docker content trust before pulling an image?

easy

A. set DOCKER_CONTENT_TRUST=1 docker pull alpine

B. docker pull --trust alpine

C. export DOCKER_CONTENT_TRUST=1 && docker pull alpine

D. docker pull alpine --enable-content-trust

Solution

1. Step 1: Recall how to enable content trust

   Content trust is enabled by setting the environment variable DOCKER_CONTENT_TRUST=1 before running docker pull.

2. Step 2: Match correct syntax

   export DOCKER_CONTENT_TRUST=1 && docker pull alpine uses the correct shell syntax to export the variable and then pull the image.

3. Final Answer:

   export DOCKER_CONTENT_TRUST=1 && docker pull alpine -> Option C

4. Quick Check:

   Set env var DOCKER_CONTENT_TRUST=1 before pull [OK]

Hint: Use export DOCKER_CONTENT_TRUST=1 before docker pull [OK]

Common Mistakes:

• Using incorrect flags like --trust or --enable-content-trust
• Trying to set env var inline without export
• Confusing Windows and Linux environment variable syntax

3. What will happen if you run docker pull alpine with DOCKER_CONTENT_TRUST=1 set but the image is unsigned?

medium

A. The image will be pulled without verification

B. Docker will automatically sign the image locally

C. Docker will pull the image but warn about missing signature

D. Docker will refuse to pull the image and show an error

Solution

1. Step 1: Understand content trust behavior on unsigned images

   When content trust is enabled, Docker requires a valid signature to pull an image.

2. Step 2: Identify expected Docker response

   If the image is unsigned, Docker refuses to pull it and shows an error to prevent unverified usage.

3. Final Answer:

   Docker will refuse to pull the image and show an error -> Option D

4. Quick Check:

   Content trust blocks unsigned image pulls [OK]

Hint: Content trust blocks unsigned images from pulling [OK]

Common Mistakes:

• Thinking Docker pulls unsigned images anyway
• Assuming Docker signs images automatically
• Believing Docker only warns but allows pull

4. You enabled content trust but get an error: no trust data available when pulling an image. What is the likely cause?

medium

A. The image has no signed tags in the registry

B. Docker daemon is not running

C. You forgot to set DOCKER_CONTENT_TRUST=0

D. Your internet connection is down

Solution

1. Step 1: Analyze the error message meaning

   'No trust data available' means Docker cannot find signed metadata for the image tags in the registry.

2. Step 2: Match cause to options

   The image has no signed tags in the registry correctly states the image lacks signed tags, causing this error when content trust is enabled.

3. Final Answer:

   The image has no signed tags in the registry -> Option A

4. Quick Check:

   No trust data = no signed tags in registry [OK]

Hint: No trust data means image tags are unsigned [OK]

Common Mistakes:

• Assuming Docker daemon stopped causes this error
• Thinking DOCKER_CONTENT_TRUST=0 fixes error when trust is needed
• Blaming internet connection without checking image signing

5. You want to ensure only signed images are deployed in your production environment. Which approach best achieves this?

hard

A. Set DOCKER_CONTENT_TRUST=1 on all production servers and pull images normally

B. Manually verify image signatures after pulling unsigned images

C. Disable content trust and rely on image tags naming conventions

D. Use docker pull --no-trust to skip signature checks

Solution

1. Step 1: Identify how to enforce signed image usage

   Setting DOCKER_CONTENT_TRUST=1 forces Docker to only pull images with valid signatures, blocking unsigned ones.

2. Step 2: Evaluate options for production safety

   Set DOCKER_CONTENT_TRUST=1 on all production servers and pull images normally correctly enforces signature verification automatically on production servers.

3. Final Answer:

   Set DOCKER_CONTENT_TRUST=1 on all production servers and pull images normally -> Option A

4. Quick Check:

   Enable content trust to enforce signed images [OK]

Hint: Enable DOCKER_CONTENT_TRUST=1 in production for safety [OK]

Common Mistakes:

• Trying to verify signatures manually after pull
• Disabling content trust and trusting tags only
• Using flags to skip trust checks in production