Running a container with docker run - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of docker run with port mapping

What will be the output when running this command?

docker run -d -p 8080:80 nginx

Assume no other containers are running and Docker is installed correctly.

A Starts a detached nginx container mapping host port 8080 to container port 80 and outputs the container ID

B Starts nginx container in foreground and outputs nginx logs

C Fails with error: port 8080 already in use

D Starts a container but does not map any ports

💡 Hint

The -d flag runs the container in detached mode, and -p maps ports.

The command runs nginx detached (-d) and maps host port 8080 to container port 80 (-p 8080:80). Docker outputs the container ID on success.

🧠 Conceptual

intermediate

Purpose of --rm flag in docker run

What does the --rm flag do when used with docker run?

A Automatically removes the container after it stops

B Restarts the container automatically if it crashes

C Removes the image after container creation

D Runs the container in read-only mode

💡 Hint

Think about container cleanup after execution.

The --rm flag tells Docker to delete the container once it stops running, keeping the system clean.

❓ Troubleshoot

advanced

Troubleshooting docker run with volume mount error

You run this command:

docker run -v /host/data:/container/data busybox ls /container/data

But get an empty output even though /host/data has files. What is the likely cause?

A The container path /container/data is incorrect and should be /data

B The busybox image does not support volume mounts

C /host/data path does not exist or is empty on the host

D Docker daemon is not running

💡 Hint

Check the host directory before running the container.

If the host directory is empty or missing, the container will show empty contents at the mount point.

🔀 Workflow

advanced

Correct order to run a container with environment variables and port mapping

Arrange these steps in the correct order to run a container with environment variable MY_VAR=hello and map port 5000 to 80:

A 1,3,2,4

B 3,1,2,4

C 2,1,3,4

D 1,2,3,4

💡 Hint

You must have the image before running the container.

First pull the image, then run with options, check running containers, then verify env variable inside.

✅ Best Practice

expert

Best practice for running containers with sensitive environment variables

Which option is the best practice to securely pass sensitive environment variables like passwords to a container using docker run?

A Use docker run -e PASSWORD=secret directly in the command line

B Store sensitive variables in a file and use --env-file option with docker run

C Hardcode sensitive variables inside the Dockerfile ENV instruction

D Pass sensitive variables as command arguments inside the container

💡 Hint

Think about avoiding exposure in command history or image layers.

Using --env-file keeps sensitive data out of command history and Dockerfile, improving security.