Docker for Beginners: A Hands-On Tutorial to Master Containers from Scratch

✅ Chapter 3: Docker Networking and Data Persistence

🔍 Overview

After mastering Docker images and containers in the previous chapters, you're now ready to tackle two vital concepts that power real-world containerized applications:

• Docker Networking: Enabling communication between containers, hosts, and the outside world.
• Docker Data Persistence: Ensuring important data survives even when containers are removed.

This chapter teaches you how to manage container communication and ensure long-term data storage using volumes and mounts.

🌐 Part 1: Docker Networking

🚀 Why Networking Matters in Docker

Containers are often part of a larger, multi-service ecosystem (e.g., app + database + cache). Docker provides flexible networking options so containers can:

• Communicate with each other
• Be isolated for security
• Expose services to the outside world

🔌 Docker Network Drivers

Docker includes multiple built-in network drivers, each serving different purposes.

🧱 Bridge Network (Default)

When you run a container without specifying a network, it connects to the bridge network by default.

bash

docker network ls

bash

docker inspect bridge

Containers on the bridge network can talk to each other using IP addresses (or container names if in the same user-defined network).

🛠️ Creating a User-Defined Network

bash

docker network create my-network

Run containers inside it:

bash

docker run -d --name app1 --network my-network nginx

docker run -d --name app2 --network my-network httpd

Now app1 can ping app2 by container name:

bash

docker exec -it app1 ping app2

🔄 Port Binding: Accessing Containers from Outside

Use the -p flag to bind container ports to host ports:

bash

docker run -d -p 8080:80 nginx

Visit http://localhost:8080 in your browser to test.

🧪 Host Network

On Linux, you can use the host's network stack:

bash

docker run --network host nginx

Useful for performance-critical scenarios but sacrifices container isolation.

❌ Isolated Containers (None Network)

bash

docker run --network none alpine

No network access. This is ideal for security testing or resource-restricted environments.

💾 Part 2: Docker Data Persistence

By default, Docker containers are ephemeral—any data inside a container disappears when it’s deleted. But most applications need persistent storage (e.g., databases, logs, configs).

Docker solves this using:

• Volumes
• Bind Mounts
• tmpfs Mounts

🧱 Docker Volumes

Volumes are managed by Docker and stored in /var/lib/docker/volumes.

🔨 Create a Volume:

bash

docker volume create mydata

🧪 Use Volume in a Container:

bash

docker run -d -v mydata:/app/data nginx

This mounts the volume mydata into /app/data inside the container.

🧾 Listing and Inspecting Volumes

bash

docker volume ls

docker volume inspect mydata

🗑️ Remove a Volume:

bash

docker volume rm mydata

Volumes are not deleted automatically when a container is removed unless --rm is used with --mount.

🗂️ Bind Mounts

Bind mounts map a host directory to a container path.

bash

docker run -v /home/user/web:/usr/share/nginx/html nginx

Useful for:

• Local development (live file changes)
• Sharing logs or configs between host and container

📊 Comparison Table: Volumes vs. Bind Mounts

📁 tmpfs Mounts

Temporary, in-memory storage:

bash

docker run --tmpfs /app/cache nginx

Data is lost when the container stops. Good for sensitive data or caching.

🧪 Practical Use Case: Containerized MySQL with Volume

bash

docker volume create mysql-data

docker run -d \

  --name mydb \

  -e MYSQL_ROOT_PASSWORD=rootpass \

  -v mysql-data:/var/lib/mysql \

  mysql:5.7

• Ensures MySQL data persists across container restarts.
• Volume mysql-data stores database files securely.

🧰 Useful Volume Commands

🧹 Clean-up Commands

• Prune unused networks:

bash

docker network prune

• Prune unused volumes:

bash

docker volume prune

• Prune all unused resources:

bash

docker system prune -a --volumes

🔐 Security Tip

• Never mount sensitive directories like /etc, /root, or /var/lib/docker unless you know exactly what you're doing.
• Use volumes, not bind mounts, for untrusted applications in production.

✅ Summary of Chapter 3

You’ve learned:

• The difference between Docker networking types: bridge, host, overlay, none
• How to connect containers using user-defined networks
• How port mapping makes services accessible from outside
• The role of volumes and bind mounts in persisting data
• Real-world usage of volume-mounting with MySQL

This knowledge is essential for building real, production-ready containerized applications.