Pushing images from CI in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Docker login command in CI?

You run this command in your CI pipeline to authenticate with Docker Hub:

docker login -u $DOCKER_USER -p $DOCKER_PASS

What will be the output if the credentials are correct?

Docker

docker login -u $DOCKER_USER -p $DOCKER_PASS

A Error: Cannot perform an interactive login from a non TTY device

B Error: Invalid username or password

C Warning: Using --password via the CLI is insecure

D Login Succeeded

💡 Hint

Think about what Docker shows when login is successful.

When Docker login succeeds, it prints 'Login Succeeded'. Other messages indicate errors or warnings.

❓ Configuration

intermediate

Which GitHub Actions step correctly pushes a Docker image to Docker Hub?

You want to push a Docker image from GitHub Actions to Docker Hub. Which step configuration will work correctly?

A

- name: Push image
  run: |
    docker push myuser/myimage:latest
  env:
    DOCKER_USER: ${{ secrets.DOCKER_USER }}
    DOCKER_PASS: ${{ secrets.DOCKER_PASS }}

B

- name: Push image
  run: |
    docker push myuser/myimage
  env:
    DOCKER_USER: ${{ secrets.DOCKER_USER }}
    DOCKER_PASS: ${{ secrets.DOCKER_PASS }}

C

- name: Push image
  run: |
    docker push myuser/myimage:latest

D

- name: Push image
  run: |
    docker push myuser/myimage:latest
  env:
    USERNAME: ${{ secrets.DOCKER_USER }}
    PASSWORD: ${{ secrets.DOCKER_PASS }}

💡 Hint

Check if the image tag is specified and environment variables match Docker login.

Option A correctly pushes the tagged image and sets environment variables matching Docker Hub credentials.

❓ Troubleshoot

advanced

Why does this CI pipeline fail to push the Docker image?

In your CI pipeline, you run:

docker build -t myuser/myimage:latest .
docker push myuser/myimage:latest

The push fails with:
denied: requested access to the resource is denied
What is the most likely cause?

A The Dockerfile has syntax errors causing build failure

B Docker Hub credentials are missing or incorrect in the CI environment

C The image tag 'latest' is not allowed by Docker Hub

D The Docker daemon is not running on the CI server

💡 Hint

Think about permissions needed to push images to Docker Hub.

The error means the CI cannot authenticate to Docker Hub, so credentials are missing or wrong.

🔀 Workflow

advanced

What is the correct order of steps to push a Docker image in a CI pipeline?

Arrange these steps in the correct order to push a Docker image from a CI pipeline:

A 4,3,1,2

B 4,3,2,1

C 4,2,3,1

D 2,4,3,1

💡 Hint

Think about setting credentials before login, then build, then push.

First set credentials, then login, then build the image, then push it.

✅ Best Practice

expert

Which practice is best to securely push Docker images from CI?

You want to push Docker images from your CI pipeline securely. Which practice is best?

A Store Docker Hub credentials as encrypted secrets in the CI system and use docker login with them

B Hardcode Docker Hub username and password in the CI pipeline script for simplicity

C Push images without authentication to a public Docker Hub repository

D Use plain text environment variables in the CI logs for easy debugging

💡 Hint

Think about security and secret management best practices.

Storing credentials securely as encrypted secrets and using them in docker login is best practice.