Docker Hub as image registry - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Docker Hub?

Docker Hub is a cloud-based service where you can store and share Docker container images with others.

beginner

How do you push a Docker image to Docker Hub?

First, tag your image with your Docker Hub username and repository name, then use the command docker push username/repository:tag.

beginner

What command logs you into Docker Hub from the command line?

Use docker login and enter your Docker Hub username and password when prompted.

beginner

Why do you need to tag a Docker image before pushing it to Docker Hub?

Tagging tells Docker where to send the image by specifying the repository and optionally the version, so Docker Hub knows how to store it.

beginner

What is the difference between a public and a private repository on Docker Hub?

Public repositories can be accessed and pulled by anyone, while private repositories are restricted and require permission to access.

Which command do you use to upload a Docker image to Docker Hub?

A docker push

B docker pull

C docker run

D docker build

docker push uploads your image to Docker Hub.

What must you do before pushing an image to Docker Hub?

A Create a Dockerfile

B Run the image locally

C Delete the image

D Tag the image with your Docker Hub repository name

You must tag the image so Docker knows where to push it.

How do you authenticate with Docker Hub from the command line?

A docker push

B docker login

C docker pull

D docker logout

docker login lets you enter your Docker Hub credentials.

What is a private repository on Docker Hub?

A A repository only accessible to authorized users

B A repository anyone can access

C A repository that stores only images you build locally

D A repository that automatically deletes images

Private repositories restrict access to selected users.

Which of these is NOT a feature of Docker Hub?

A Storing Docker images

B Sharing images publicly or privately

C Running containers in the cloud

D Automated builds from GitHub

Docker Hub stores images but does not run containers.

Explain the steps to push a Docker image to Docker Hub.

Think about logging in, tagging, then pushing.

Describe the difference between public and private repositories on Docker Hub.

Consider who can see and use the images.

Practice

1. What is Docker Hub primarily used for in Docker workflows?

easy

A. A public registry to store and share Docker images

B. A tool to build Docker images locally

C. A command-line interface for managing containers

D. A service to monitor running Docker containers

Solution

1. Step 1: Understand Docker Hub's role

   Docker Hub is a cloud-based service where users can upload and download Docker images.

2. Step 2: Differentiate from other Docker tools

   Building images is done locally with Docker CLI, not Docker Hub. Docker Hub is for storing and sharing images.

3. Final Answer:

   A public registry to store and share Docker images -> Option A

4. Quick Check:

   Docker Hub = Image registry [OK]

Hint: Docker Hub = place to store/share images [OK]

Common Mistakes:

• Confusing Docker Hub with Docker CLI commands
• Thinking Docker Hub builds images
• Assuming Docker Hub manages running containers

2. Which command correctly logs you into Docker Hub from the terminal?

easy

A. docker login

B. docker push

C. docker pull

D. docker build

Solution

1. Step 1: Identify the login command

   The command docker login prompts for Docker Hub credentials to authenticate the user.

2. Step 2: Understand other commands

   docker push uploads images, docker pull downloads images, and docker build creates images locally.

3. Final Answer:

   docker login -> Option A

4. Quick Check:

   Login command = docker login [OK]

Hint: Use 'docker login' to authenticate with Docker Hub [OK]

Common Mistakes:

• Using 'docker push' to login
• Confusing 'docker pull' with login
• Trying to login with 'docker build'

3. What will happen if you run docker push myuser/myapp:latest without logging into Docker Hub first?

medium

A. Docker will create a new repository automatically

B. Docker will prompt for login credentials

C. The image will be pushed successfully

D. The command will fail with an authentication error

Solution

1. Step 1: Understand authentication requirement for push

   Pushing images to Docker Hub requires authentication; without login, Docker cannot verify permissions.

2. Step 2: Result of pushing without login

   Docker will reject the push and show an authentication error instead of prompting or succeeding.

3. Final Answer:

   The command will fail with an authentication error -> Option D

4. Quick Check:

   Push without login = auth error [OK]

Hint: Push needs login; no login causes auth error [OK]

Common Mistakes:

• Expecting Docker to prompt for login automatically
• Assuming push works without authentication
• Thinking Docker creates repos automatically on push

4. You tried to push an image with docker push myuser/myapp but got an error: denied: requested access to the resource is denied. What is the most likely cause?

medium

A. You forgot to tag the image with your Docker Hub username

B. Docker daemon is not running

C. You are not logged into Docker Hub or lack permission

D. The image name contains invalid characters

Solution

1. Step 1: Analyze the error message

   The error means Docker Hub rejected access, usually due to missing login or permission issues.

2. Step 2: Check common causes

   Not being logged in or lacking rights to push to that repository causes this error, even if tagging is correct.

3. Final Answer:

   You are not logged into Docker Hub or lack permission -> Option C

4. Quick Check:

   Access denied = login or permission issue [OK]

Hint: Access denied usually means login or permission problem [OK]

Common Mistakes:

• Assuming tagging is always the cause
• Ignoring login status
• Thinking Docker daemon stopped causes this error

5. You want to share a custom Docker image named myapp with your team using Docker Hub. Which sequence of commands correctly tags and pushes the image to your Docker Hub repository myuser/myapp?

hard

A. docker login && docker build myapp && docker push myuser/myapp

B. docker tag myapp myuser/myapp:latest && docker push myuser/myapp:latest

C. docker push myapp && docker tag myuser/myapp:latest

D. docker pull myapp && docker tag myuser/myapp && docker push

Solution

1. Step 1: Tag the local image with your Docker Hub repo name

   Use docker tag myapp myuser/myapp:latest to prepare the image for pushing.

2. Step 2: Push the tagged image to Docker Hub

   Run docker push myuser/myapp:latest to upload the image to your Docker Hub repository.

3. Final Answer:

   docker tag myapp myuser/myapp:latest && docker push myuser/myapp:latest -> Option B

4. Quick Check:

   Tag then push = correct sequence [OK]

Hint: Tag image with repo name before pushing [OK]

Common Mistakes:

• Pushing without tagging the image
• Pushing before tagging or building
• Confusing pull with push commands