Why images are blueprints for containers in Docker - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

What best describes a Docker image?

Choose the option that correctly explains what a Docker image is.

A A running instance of an application with its own filesystem and processes.

B A static file that contains all the instructions and files needed to create a container.

C A command used to start a container from a blueprint.

D A network configuration for connecting multiple containers.

💡 Hint

Think about what you need before you can run a container.

A Docker image is like a recipe or blueprint. It contains all the files and instructions needed to create a container. Containers are created from images.

💻 Command Output

intermediate

Output of listing Docker images

What is the expected output of the command docker images?

A Lists all running containers with their IDs and status.

B Displays the logs of the last container started.

C Shows all available Docker images with repository, tag, and size.

D Removes all unused Docker images from the system.

💡 Hint

Think about what you want to see when you ask for images.

The docker images command lists all Docker images stored locally, showing details like repository name, tag, image ID, creation date, and size.

🔀 Workflow

advanced

Order of steps to create and run a container from an image

Arrange the steps in the correct order to create and run a container from a Docker image.

A 3,1,2,4

B 1,3,2,4

C 3,2,1,4

D 2,1,3,4

💡 Hint

Think about how you first define, then get, then run, then check.

First, you write a Dockerfile to define the image (3). Then you build or pull the image (1). Next, you run a container from that image (2). Finally, you verify the container is running (4).

❓ Troubleshoot

advanced

Why does a container fail to start from an image?

You try to start a container from an image but it immediately stops. Which is the most likely reason?

A The image size is too large to run.

B The Docker daemon is not installed on the host.

C The container is running in detached mode.

D The image does not contain a command or entrypoint to run.

💡 Hint

Think about what a container needs to do when it starts.

If an image lacks a command or entrypoint, the container has nothing to run and will stop immediately after starting.

✅ Best Practice

expert

Why should Docker images be kept small?

Which is the best reason to keep Docker images small and minimal?

A Smaller images start faster and use less disk space, improving deployment speed and resource use.

B Small images automatically update themselves without manual intervention.

C Large images cannot be pushed to Docker Hub due to size limits.

D Small images allow containers to run without a Docker daemon.

💡 Hint

Think about speed and storage when deploying containers.

Keeping images small helps containers start quickly and reduces storage and network use, making deployments efficient.