What is Docker - Practice Questions & Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of Docker?

Docker is a popular tool in DevOps. What is its main purpose?

A To create isolated environments called containers to run applications consistently.

B To manage virtual machines with heavy resource usage.

C To monitor network traffic between servers.

D To write code in multiple programming languages.

💡 Hint

Think about how Docker helps developers run apps the same way everywhere.

Docker creates containers that package an application and its dependencies, ensuring it runs the same on any system.

💻 Command Output

intermediate

What is the output of 'docker ps' command?

After running docker ps on a system with two running containers, what will you see?

Docker

docker ps

A A list showing details of all running containers including container ID, image, status, and ports.

B A list of all images downloaded on the system.

C A list of all stopped containers only.

D An error saying 'command not found'.

💡 Hint

Remember, docker ps shows running containers, not images or stopped containers.

The docker ps command lists all currently running containers with their details.

❓ Configuration

advanced

Which Dockerfile instruction sets the base image?

In a Dockerfile, which instruction is used to specify the base image for your container?

Docker

Dockerfile snippet

A CMD python app.py

B RUN apt-get update

C COPY . /app

D FROM ubuntu:20.04

💡 Hint

The base image is the starting point for your container's environment.

The FROM instruction sets the base image in a Dockerfile, defining the starting environment.

🔀 Workflow

advanced

What is the correct order to build and run a Docker container?

Arrange these steps in the correct order to build and run a Docker container from a Dockerfile.

A 3,2,1,4

B 3,1,2,4

C 1,3,2,4

D 2,1,3,4

💡 Hint

First create the Dockerfile, then build the image, run the container, and finally check it.

You must write the Dockerfile first, then build the image, run the container, and check its status.

❓ Troubleshoot

expert

What error occurs if Docker daemon is not running when executing 'docker ps'?

You run docker ps but get an error. What is the most likely error message if the Docker daemon is not running?

A Error: No such container found.

B Syntax error near unexpected token 'ps'.

C Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

D Permission denied while accessing Dockerfile.

💡 Hint

Think about what happens if the Docker service is stopped but you try to use Docker commands.

If the Docker daemon is not running, commands like docker ps cannot connect and show this error.