🚀 Docker Advance Guide for DevOps Learners ( Part 3 )

Welcome to Part 3 of our Docker series! In this blog, we dive deeper into advanced Docker concepts including Volumes, Networks, and Docker Compose with multi-stage builds. If you're building real-world applications with Docker, this guide will help you organize and scale like a pro! 🧱

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📂 Docker Volumes

✅ What is a Docker Volume?

A Docker volume is a persistent storage mechanism. It allows container data to survive restarts, and even deletion of the container. It acts as a bridge between the container and the host filesystem.

"Volume = Backup container data to host."

📑 Example with MySQL

Step-by-step:

mkdir mysql-volume
pwd  # Copy this path

Run MySQL container:

docker run -d \
  -v /home/ubuntu/mysql-volume:/var/lib/mysql \
  --name mysql \
  -e MYSQL_ROOT_PASSWORD=Test@123 \
  mysql:latest

Verify container:

docker ps

Enter container and start MySQL:

docker exec -it <container_id> bash
mysql -u root -p

Now inside MySQL:

CREATE DATABASE kyc_devops;
USE kyc_devops;

CREATE TABLE messages (
  id INT AUTO_INCREMENT PRIMARY KEY,
  message TEXT
);

INSERT INTO messages (message) VALUES ("kyc submitted");
SELECT * FROM messages;

Check volume data:

cd mysql-volume
ls

🪤 Volume Explanation

• -v host_path:/container_path

• Host path /home/ubuntu/mysql-volume maps to /var/lib/mysql inside container

🌟 Volume Use Cases

• Data persistence for DBs

• Share data between containers

📊 Logical Named Volume

docker volume create mysql-volume

Inspect:

docker volume ls
docker volume inspect mysql-volume

Mount named volume:

docker run -d \
  -v mysql-volume:/var/lib/mysql \
  --name mysql \
  -e MYSQL_ROOT_PASSWORD=Test@123 \
  mysql:latest

Same for NGINX:

docker run -d -v nginx-volume:/var/lib/ -p 80:80 nginx:latest

🌐 Port Mapping

# Format: host_port:container_port
-p 80:80

📉 Volume Errors:

• Use sudo su if cd nginx-volume shows permission denied

• Remove volume:

docker volume rm nginx-volume

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🛀 Docker Networking

✅ Definition

Docker networking allows containers to communicate securely and efficiently across different environments.

🪤 Types of Networks

🌟 User Defined Bridge Network

Create:

docker network create -d bridge twotier

Run MySQL container:

docker run -d --name mysql \
  -v mysql-volume:/var/lib/mysql \
  -e MYSQL_DATABASE=mydb \
  -e MYSQL_ROOT_PASSWORD=Test@123 \
  -p 3306:3306 \
  --network=twotier \
  mysql:latest

Run Flask app:

docker run -d --name flaskapp \
  -e MYSQL_HOST=mysql \
  -e MYSQL_USER=root \
  -e MYSQL_ROOT_PASSWORD=Test@123 \
  -e MYSQL_DB=mydb \
  -p 5000:5000 \
  --network=twotier \
  flaskapp:latest

Inspect network:

docker network inspect twotier

✅ Both containers should appear under the Containers section — showing they're linked.

📅 Final Step - EC2 Access

Go to:

• AWS Console > EC2 > Security Groups > Edit Inbound Rules

• Add port 5000 and set Source to Anywhere

Check app:

<public-ip>:5000

Now the containers are communicating properly!

Default ( bridge ) Networks vs. User-Defined ( bridge ) Networks

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✅ Example of Default bridge Network

bashCopyEditdocker run -d --name container1 nginx
docker run -d --name container2 busybox

• Both are in bridge network.

• To ping: use IP address (e.g. ping 172.17.0.2) — not container name.

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✅ Example of user-defined bridge Network

bashCopyEditdocker network create mynetwork

docker run -d --name mysql --network=mynetwork mysql
docker run -d --name flaskapp --network=mynetwork flaskapp

• Now flaskapp can talk to mysql using mysql as hostname. ✅

• Better for Docker Compose, Microservices, and DevOps setups.

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💡 Summary

✅ User-defined networks = Want name-based communication, better control, and production-readiness + More control, DNS, isolation, security.

❌ Default networks = Want easy setup but limited features + Simple but limited (no DNS, shared IP space).

📅 Docker Prune

📝 Use Case

To clean unused Docker objects like stopped containers, unused volumes, and networks.

🔎 Commands:

docker system prune
# Clean everything

docker volume prune
# Clean unused volumes

docker network prune
# Clean unused networks

docker image prune
# Clean dangling images

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📄 Docker Compose:

✅ Meaning

Docker Compose allows defining and running multi-container applications using a YAML file.

📂 Installation (Linux)

sudo apt-get update
sudo apt-get install docker-compose-plugin

📚 Flask App Compose File

version: "3.8"

services:
  mysql:
    image: mysql:latest
    container_name: mysql
    environment:
      MYSQL_ROOT_PASSWORD: Test@123
      MYSQL_DATABASE: mydb
    volumes:
      - mysql-volume:/var/lib/mysql
    networks:
      - twotier

  flaskapp:
    build:
      context: .
      dockerfile: Dockerfile
    container_name: flaskapp
    environment:
      MYSQL_HOST: mysql
      MYSQL_USER: root
      MYSQL_ROOT_PASSWORD: Test@123
      MYSQL_DB: mydb
    ports:
      - "5000:5000"
    networks:
      - twotier

volumes:
  mysql-volume:

networks:
  twotier:

get code/file from:

git clone git@github.com:abhishek26w/Docker.git

& click on day-2

🌟 Commands:

docker compose config
# Validate YAML file

docker compose up
# Start all services

docker compose up -d
# Detached mode

docker compose down
# Stop and remove all

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🏗 Multi-Stage Dockerfile — Optimize Your Images

✅ Definition

Break image creation into stages — build in one, run in another — smaller and cleaner images.

Multi-stage = Clean build + lightweight runtime 🚀

📚 Example: Python Flask App

# Stage 1 - Build
FROM python:3.10-slim as builder
WORKDIR /app
COPY requirements.txt .
RUN pip install --user -r requirements.txt
COPY . .

# Stage 2 - Run
FROM python:3.10-slim
WORKDIR /app
COPY --from=builder /app /app
CMD ["python", "app.py"]

⚠️ Common Errors

• permission denied from mysql-data: Use

    sudo chown -R $USER:$USER mysql-volume
  

• buildx error: Use

    docker buildx install
  

  🚨 Final Steps

sudo curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh get-docker.sh
newgrp docker

Check:

docker version
docker compose version

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🗒 Summary

• 📦 Docker Volume

• 🌐 Docker Network

• 🧩 Docker Compose

• 🏗 Multi-Stage Builds

Boost your DevOps power by mastering these tools! 💪

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