Mounting read-only volumes in Docker - Mini Project: Build & Apply

Mounting Read-Only Volumes in Docker

📖 Scenario: You are working on a Docker container that needs to access some files from your host machine. To keep the container safe and prevent accidental changes, you want to mount the files as read-only.

🎯 Goal: Learn how to mount a host directory into a Docker container as a read-only volume.

📋 What You'll Learn

Create a Docker volume mount command with a host directory

Add a read-only flag to the volume mount

Run a container that uses the read-only volume

Verify the volume is mounted as read-only inside the container

💡 Why This Matters

🌍 Real World

Mounting read-only volumes is useful when you want to share configuration files or data with containers without risking accidental changes.

💼 Career

Understanding volume mounts and permissions is essential for container management and deployment in DevOps roles.

1

Create a host directory with a file

Create a directory called mydata in your current folder and inside it create a file named info.txt with the text Hello Docker.

Docker

# Create the directory and file on your host machine
# Your code here

Need a hint?

Use mkdir -p mydata to create the directory and echo to write text to the file.

2

Write the Docker run command with volume mount

Write a docker run command that starts an alpine container and mounts the host directory mydata to /data inside the container.

Docker

mkdir -p mydata
echo "Hello Docker" > mydata/info.txt
# Write the docker run command with volume mount here
# Your code here

Need a hint?

Use -v $(pwd)/mydata:/data to mount the directory.

3

Add the read-only flag to the volume mount

Modify the docker run command to mount the volume as read-only by adding :ro at the end of the volume mount.

Docker

mkdir -p mydata
echo "Hello Docker" > mydata/info.txt
docker run --rm -it -v $(pwd)/mydata:/data alpine sh
# Add :ro to the volume mount to make it read-only
# Your code here

Need a hint?

Add :ro after the container path in the volume mount to make it read-only.

4

Verify the volume is read-only inside the container

Inside the running container, try to create a new file /data/newfile.txt. Use the command touch /data/newfile.txt and observe the output. Then print the contents of /data/info.txt using cat /data/info.txt.

Docker

mkdir -p mydata
echo "Hello Docker" > mydata/info.txt
docker run --rm -it -v $(pwd)/mydata:/data:ro alpine sh
# Inside container, try to create a file and read the existing file
# Your code here

Need a hint?

The touch command should fail because the volume is read-only. The cat command should display Hello Docker.