Docker login and authentication - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of a successful Docker login?

You run the command docker login and enter valid credentials for Docker Hub. What output do you see?

Docker

docker login

A Error: unauthorized: incorrect username or password

B Login Succeeded

C Cannot connect to the Docker daemon

D Warning: login credentials expired

💡 Hint

Think about what message confirms a successful login.

When you login successfully to Docker Hub, the message Login Succeeded is shown.

🧠 Conceptual

intermediate

What does the Docker config file store after login?

After running docker login, Docker stores authentication info locally. What does the config file typically contain?

A Encrypted tokens or credentials for registries

B List of all pulled images

C Docker daemon configuration settings

D Plain text passwords for all registries

💡 Hint

Think about security and what should be stored safely.

Docker stores encrypted tokens or credentials in ~/.docker/config.json after login, not plain passwords.

❓ Troubleshoot

advanced

Why does docker login fail with 'unauthorized' error?

You run docker login with your username and password but get unauthorized: incorrect username or password. What is the most likely cause?

A Docker client version is outdated

B Docker daemon is not running

C Docker Hub service is down

D Incorrect username or password entered

💡 Hint

Check your credentials carefully.

This error means the username or password is wrong. The daemon or client version would cause different errors.

🔀 Workflow

advanced

What is the correct sequence to authenticate and push an image to a private registry?

You want to push a Docker image to a private registry that requires login. Which sequence of commands is correct?

A docker push myimage; docker login registry.example.com; docker tag myimage registry.example.com/myimage

B docker tag myimage registry.example.com/myimage; docker push registry.example.com/myimage; docker login registry.example.com

C docker login registry.example.com; docker tag myimage registry.example.com/myimage; docker push registry.example.com/myimage

D docker login registry.example.com; docker push myimage; docker tag myimage registry.example.com/myimage

💡 Hint

Login must happen before pushing, and tagging must happen before push with the registry prefix.

You must login first, then tag your image with the registry URL, then push it.

✅ Best Practice

expert

Which method is best to securely authenticate Docker in automated CI/CD pipelines?

In a CI/CD pipeline, you want to authenticate Docker to push images without exposing your password. Which method is best practice?

A Use Docker access tokens or secrets stored securely in the pipeline environment

B Use Docker login with username and password interactively during the pipeline

C Store your Docker Hub password in plain text in the pipeline config

D Skip authentication and push images anonymously

💡 Hint

Think about security and automation without manual input.

Using access tokens or secrets securely stored in the pipeline environment is best practice for automated authentication.