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lab5-docker-storage.md

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Hands-On Lab: Exploring Docker Storage Drivers and Persistent Data Management

Lab Objective

In this lab, students will:

  1. Understand Docker storage drivers and their role in container storage.
  2. Experiment with Docker's writable layer and observe data persistence behavior.
  3. Use Docker volumes and bind mounts for persistent storage.

Prerequisites

  • Docker installed on your Linux system.
  • Basic understanding of Docker concepts.

Part 1: Exploring the Writable Layer

Step 1.1: Run a Temporary Container

Start a container using the alpine image:

docker run -dit --name temp-container alpine sh

Step 1.2: Create Files Inside the Container

Access the container shell and create a file:

docker exec -it temp-container sh
touch /test-file
echo "Hello, Docker!" > /test-file
cat /test-file

Step 1.3: Stop and Remove the Container

Stop and remove the container:

docker stop temp-container
docker rm temp-container

Step 1.4: Verify File Persistence

Run a new container with the same image and check if the file exists:

docker run -it alpine sh
ls /test-file

Observation:
The file is no longer available, demonstrating that data in the writable layer is not persistent.

Part 2: Experimenting with Storage Drivers

Step 2.1: Check the Current Storage Driver

Find the storage driver Docker is using:

docker info | grep "Storage Driver"

Step 2.2: Inspect Container Layers

Inspect the layers of an image:

docker image inspect alpine

Run a container, make changes, and inspect its layers:

docker run -dit --name layer-test alpine sh
docker exec -it layer-test sh -c "echo 'Layer Test' > /layer-file"
docker commit layer-test layer-image
docker image inspect layer-image

Part 3: Using Docker Volumes

Step 3.1: Create a Volume

Create a named volume:

docker volume create my-volume

Step 3.2: Attach the Volume to a Container

Run a container with the volume attached:

docker run -dit --name volume-container -v my-volume:/data alpine sh

Step 3.3: Write Data to the Volume

Access the container shell and create a file in the volume:

docker exec -it volume-container sh
echo "Persistent data" > /data/persistent-file

Step 3.4: Verify Data Persistence

Stop and remove the container, then attach the volume to a new container:

docker stop volume-container
docker rm volume-container
docker run -it --name new-container -v my-volume:/data alpine sh
cat /data/persistent-file

Observation:
Data in the volume persists across container lifecycles.

Part 4: Using Bind Mounts

Step 4.1: Create a Directory on the Host

Create a directory on your host system:

mkdir ~/docker-bind-mount
echo "Hello from Host!" > ~/docker-bind-mount/host-file

Step 4.2: Attach the Directory as a Bind Mount

Run a container with the directory mounted:

docker run -dit --name bind-container -v ~/docker-bind-mount:/app alpine sh

Step 4.3: Access and Modify the Bind Mount

Access the container shell and verify the contents:

docker exec -it bind-container sh
ls /app
cat /app/host-file
echo "Modified by Container" >> /app/host-file

Verify changes from the host:

cat ~/docker-bind-mount/host-file

Part 5: Cleaning Up

Remove all containers, volumes, and temporary files created during the lab:

docker rm -f $(docker ps -aq)
docker volume rm my-volume
rm -r ~/docker-bind-mount

Key Takeaways

  1. The writable layer in Docker is temporary and tied to the container's lifecycle.
  2. Docker volumes provide persistent storage that is independent of container lifecycles.
  3. Bind mounts enable direct interaction between host filesystems and containers.
  4. Storage drivers play a critical role in managing container storage layers.