Module 5: Docker Volumes & Storage

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In the last module, we explored Docker Networking and learned how containers communicate with each other. Now, let’s focus on data persistence—one of the most important aspects of running real-world applications.

By the end of this module, you’ll understand:

• The difference between bind mounts and volumes

• How to create and manage Docker volumes

• How to persist database data using volumes

• How to share data between multiple containers

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🔹 1. Difference Between Bind Mounts and Volumes

Docker containers are ephemeral by default—once removed, all their data is gone. To persist data, Docker provides two main mechanisms:

🔸 Bind Mounts

• Map a directory from the host machine into the container.

• Useful for development (syncing code between host & container).

• Example:

    docker run -v $(pwd):/app nginx
  

  👉 This mounts your current directory into /app inside the container.

🔸 Volumes

• Managed directly by Docker.

• Stored in Docker’s internal location (/var/lib/docker/volumes/).

• More portable, secure, and recommended for production.

• Example:

    docker run -v mydata:/app/data nginx
  

👉 Rule of thumb: Use bind mounts for local dev, and volumes for production.

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🔹 2. Creating and Managing Volumes

Create a volume

docker volume create my-volume

List volumes

docker volume ls

Inspect a volume

docker volume inspect my-volume

Remove a volume

docker volume rm my-volume

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🔹 3. Persisting Database Data with Volumes

Let’s see why volumes are crucial with databases.

Example: MySQL without a volume

docker run --name db1 -e MYSQL_ROOT_PASSWORD=root -d mysql:8.0

• If you remove this container, all data is gone ❌.

Now with a volume:

docker run --name db2 -e MYSQL_ROOT_PASSWORD=root \
  -v mysql_data:/var/lib/mysql -d mysql:8.0

• mysql_data volume stores the database files.

• Even if you remove the container, the data persists ✅.

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🔹 4. Sharing Data Between Containers

Volumes can also be shared across multiple containers.

Example:

# Create a volume
docker volume create shared-data

# Start first container writing to volume
docker run -d --name writer -v shared-data:/data alpine sh -c "echo 'Hello from Writer' > /data/file.txt && tail -f /dev/null"

# Start second container reading from volume
docker run -it --name reader -v shared-data:/data alpine cat /data/file.txt

👉 The second container (reader) can access data written by the first container (writer).

This is extremely useful for scenarios like:

• Multiple containers accessing logs

• Web apps and workers sharing files

• Database + admin tools accessing the same data

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🚀 Quick Recap

In this module, you learned:
✅ Difference between bind mounts and volumes
✅ How to create and manage volumes
✅ How to persist database data
✅ How to share data between containers

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