Pushing images to registry in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Docker push command?

You run the command docker push myrepo/myimage:latest but you are not logged in. What output will you see?

Docker

docker push myrepo/myimage:latest

A Error response from daemon: unauthorized: authentication required

B Pushed image successfully to myrepo/myimage:latest

C Error: No such image: myrepo/myimage:latest

D Warning: tag latest not found in repository myrepo/myimage

💡 Hint

Think about what happens if you try to push without logging in first.

Docker requires authentication to push images to a registry. Without logging in, the push command fails with an unauthorized error.

🧠 Conceptual

intermediate

Which step is required before pushing a Docker image to a private registry?

You want to push your Docker image to a private registry. What must you do first?

A Run <code>docker pull</code> to download the image

B Run <code>docker login</code> with the registry credentials

C Run <code>docker build</code> with the <code>--push</code> flag

D Run <code>docker logout</code> to clear old credentials

💡 Hint

Think about how Docker authenticates with registries.

You must authenticate with the registry using docker login before pushing images to it.

❓ Troubleshoot

advanced

Why does this Docker push fail with 'denied: requested access to the resource is denied'?

You tagged your image as myrepo/myimage:latest and ran docker push myrepo/myimage:latest. The push fails with:
denied: requested access to the resource is denied
What is the most likely cause?

A You do not have permission to push to the repository 'myrepo/myimage'

B You forgot to run 'docker pull' before pushing

C Docker daemon is not running

D The image tag 'latest' does not exist locally

💡 Hint

Consider repository permissions and ownership.

This error usually means your user account lacks permission to push to that repository on the registry.

🔀 Workflow

advanced

Order the steps to push a Docker image to Docker Hub

Put these steps in the correct order to push a Docker image to Docker Hub:

A 4,3,1,2

B 3,1,4,2

C 3,4,1,2

D 1,3,4,2

💡 Hint

You must authenticate before pushing, but after building the image.

First build the image, then log in, then tag it properly, then push.

✅ Best Practice

expert

Which practice helps avoid pushing large unused layers to a registry?

You want to optimize your Docker image pushes to reduce size and speed. Which practice is best?

A Use 'docker push --compress=false' to speed up pushing

B Always push images with the 'latest' tag

C Run 'docker system prune' before pushing

D Use multi-stage builds to keep only necessary layers

💡 Hint

Think about how to reduce image size before pushing.

Multi-stage builds allow you to discard build-time layers, keeping images smaller and push faster.