Pulling from private registries in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to log in to a private Docker registry.

Docker

docker [1] myregistry.example.com

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

Apull

Bpush

Clogin

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'docker pull' instead of 'docker login' to authenticate.

Trying to use 'docker run' to log in.

The docker login command is used to authenticate with a private Docker registry.

2fill in blank

medium

Complete the command to pull an image from a private registry after login.

Docker

docker [1] myregistry.example.com/myimage:latest

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

Alogin

Bpull

Cpush

Dbuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'docker login' instead of 'docker pull' to get images.

Using 'docker push' which uploads images instead of downloading.

The docker pull command downloads an image from a registry to your local machine.

3fill in blank

hard

Fix the error in the command to pull from a private registry by adding the missing option.

Docker

docker pull [1]/myimage:latest

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

Amyregistry.example.com

Blatest

Cdocker.io

Dlibrary

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the registry URL causes Docker to look in the public registry.

Using 'latest' or 'library' instead of the registry URL.

When pulling from a private registry, you must specify the registry URL before the image name.

4fill in blank

hard

Fill both blanks to create a Docker config file path and command to use it for authentication.

Docker

docker --config [1] [2] myregistry.example.com

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

A~/.docker

Blogin

Cpull

D/etc/docker

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pull' instead of 'login' with the config option.

Using '/etc/docker' which is less common for user config.

The --config option points to the Docker config directory, and login authenticates to the registry.

5fill in blank

hard

Fill the blanks to create a command that logs in with username and password from environment variables.

Docker

echo $[1] | docker login myregistry.example.com -u $[2] --password-stdin

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

APASSWORD

BUSERNAME

CUSER

DPASS

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up USER and USERNAME variables.

Not using --password-stdin to securely pass the password.

This command uses the environment variable PASSWORD piped into docker login with username from USERNAME variable.

Practice

1. What is the first step to pull an image from a private Docker registry?

easy

A. Run docker login with the registry URL to authenticate.

B. Directly run docker pull without authentication.

C. Create a Dockerfile to build the image locally.

D. Restart the Docker daemon.

Solution

1. Step 1: Understand private registry access

   Private registries require authentication before pulling images to ensure security.

2. Step 2: Use the correct command for authentication

   The docker login command with the registry URL authenticates the user.

3. Final Answer:

   Run docker login with the registry URL to authenticate. -> Option A

4. Quick Check:

   Authentication = docker login [OK]

Hint: Always login first to private registries before pulling images [OK]

Common Mistakes:

• Trying to pull without login causes permission errors
• Confusing image build with pulling
• Restarting Docker daemon is unrelated

2. Which of the following is the correct syntax to login to a private Docker registry at myregistry.example.com?

easy

A. docker login myregistry.example.com

B. docker pull myregistry.example.com

C. docker push myregistry.example.com

D. docker build myregistry.example.com

Solution

1. Step 1: Identify the login command

   The docker login command is used to authenticate to a registry.

2. Step 2: Use the registry URL as argument

   Adding the registry URL after docker login targets that specific private registry.

3. Final Answer:

   docker login myregistry.example.com -> Option A

4. Quick Check:

   Login syntax = docker login [OK]

Hint: Use 'docker login' plus registry URL to authenticate [OK]

Common Mistakes:

• Using pull or push commands instead of login
• Omitting the registry URL when needed
• Confusing build command with login

3. What will be the output if you run the following commands in order?

docker login myregistry.example.com
docker pull myregistry.example.com/myapp:latest

medium

A. Error: unauthorized: authentication required

B. Image 'myapp:latest' downloaded successfully from myregistry.example.com

C. Error: repository not found

D. Docker daemon restart required

Solution

1. Step 1: Authenticate with the private registry

   The docker login command authenticates the user successfully.

2. Step 2: Pull the image after authentication

   Since the user is logged in, docker pull downloads the private image without errors.

3. Final Answer:

   Image 'myapp:latest' downloaded successfully from myregistry.example.com -> Option B

4. Quick Check:

   Login then pull = success [OK]

Hint: Login first, then pull to avoid unauthorized errors [OK]

Common Mistakes:

• Pulling without login causes unauthorized errors
• Assuming image is public without checking
• Expecting daemon restart after login

4. You tried to pull an image from a private registry but got this error:
Error response from daemon: unauthorized: authentication required
What is the most likely cause and fix?

medium

A. The image name is misspelled; correct the image name.

B. Your internet connection is down; check network.

C. Docker daemon is not running; restart Docker service.

D. You forgot to run docker login before pulling; run login first.

Solution

1. Step 1: Analyze the error message

   The error says authentication is required, meaning no valid login was done.

2. Step 2: Apply the fix by authenticating

   Running docker login with the registry URL will authenticate and fix the error.

3. Final Answer:

   You forgot to run docker login before pulling; run login first. -> Option D

4. Quick Check:

   Unauthorized error = missing login [OK]

Hint: Unauthorized error means login missing; run docker login [OK]

Common Mistakes:

• Assuming image name typo causes unauthorized error
• Restarting Docker daemon unnecessarily
• Blaming network without checking login

5. You want to automate pulling a private image from registry.example.com in a script. Which sequence of commands correctly handles authentication and pulling?

hard

A. docker build registry.example.com/myimage:latest && docker login registry.example.com

B. docker pull registry.example.com/myimage:latest && docker login registry.example.com

C. docker login registry.example.com && docker pull registry.example.com/myimage:latest

D. docker logout registry.example.com && docker pull registry.example.com/myimage:latest

Solution

1. Step 1: Authenticate before pulling

   Use docker login first to authenticate to the private registry.

2. Step 2: Pull the image after successful login

   Run docker pull to download the private image after authentication.

3. Final Answer:

   docker login registry.example.com && docker pull registry.example.com/myimage:latest -> Option C

4. Quick Check:

   Login then pull = correct sequence [OK]

Hint: Login first, then pull in scripts using && [OK]

Common Mistakes:

• Pulling before login causes failure
• Using build instead of pull for images
• Logging out before pulling removes credentials