Introduction to Docker Compose

Docker Compose is a powerful tool that allows you to define and manage multi-container Docker applications. With Docker Compose, you can define your application’s services, networks, and volumes in a simple YAML file, and then run your entire application with a single command.

Basic Structure of a YAML File

A YAML file is used to configure the services, networks, and volumes that your Docker application will use. The basic structure of a YAML file is:

Steps to Install, Run & Stop Docker Compose

Install Docker Compose:

 sudo apt-get install docker-compose-v2

Run the containers / yml file:
```
 docker-compose up -d
```
The -d flag runs the containers in detached mode.
Stop the containers:
```
 docker-compose down
```
This command stops and removes all containers defined in your docker-compose.yml file.

Example of a Docker Compose YAML File

Here is an example YAML file that defines a two-tier application with a MySQL database and a Flask application:

version: '3.9'
services:
  mysql:
    container_name: mysql
    image: mysql:5.7
    ports:
      - "3306:3306"
    environment:
      MYSQL_ROOT_PASSWORD: test@123
      MYSQL_DATABASE: devops
    volumes:
      - mysql-data:/var/lib/mysql
    networks:
      - twotier
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "localhost", "-u", "root", "-p$MYSQL_ROOT_PASSWORD"]
      interval: 10s
      retries: 5
      start_period: 30s

  two-tier-app:
    container_name: two-tier-app
    build:
      context: .
    ports:
      - "5000:5000"
    environment:
      MYSQL_HOST: mysql
      MYSQL_USER: root
      MYSQL_PASSWORD: test@123
      MYSQL_DB: devops
    depends_on:
      mysql:
        condition: service_healthy
    networks:
      - twotier

volumes:
  mysql-data:
networks:
  twotier:
    driver: bridge

Multi-Stage Builds in Docker

Multi-stage builds allow you to create smaller, more efficient Docker images by separating the build process into multiple stages.

Here's an example:

# Stage 1: Build
FROM python:3.11 AS backend-builder
WORKDIR /app
COPY . .
RUN pip install -r requirements.txt

# Stage 2: Final Image
FROM python:3.11-slim
WORKDIR /app
COPY --from=backend-builder /usr/local/lib/python3.11/site-packages/ /usr/local/lib/python3.11/site-packages
COPY --from=backend-builder /app /app
CMD ["python","app.py"]

Docker Scout

Docker Scout is a tool that helps you analyze and understand the security risks in your Docker images by identifying Common Vulnerabilities and Exposures (CVEs).

Steps to Install Docker Scout:

Pull Docker Scout from Docker Hub:
```
 docker pull docker/scout:latest
```
Make .docker directory:
```
 mkdir -p $HOME/.docker/scout
```

Run the curl command:

 curl -fsSL https://raw.githubusercontent.com/docker/scout-cli/main/install.sh -o install-scout.sh
 sh install-scout.sh

Login to Docker Hub using PAT:

 docker login --username YOUR_USERNAME --password YOUR_PAT

Run CVE Scanning on MySQL:
```
 docker scout cves mysql:latest
```
QuickScan:
```
 docker scout quickview mysql:latest
```

Pushing and Pulling Images on Docker Hub

Push an Image to Docker Hub:

 docker tag local-image-name dockerhub-username/repository-name:tag
 docker push dockerhub-username/repository-name:tag

Pull an Image from Docker Hub:

 docker pull dockerhub-username/repository-name:tag

Docker Init

docker init is a command that helps you quickly set up a Dockerized project by generating a Dockerfile and other configuration files based on your project structure.

Conclusion

Docker Compose and multi-stage builds are essential tools in modern software development, allowing for efficient, scalable, and secure application deployment. By leveraging Docker's capabilities, I was able to create, connect, and manage containers seamlessly, contributing to a more streamlined and automated DevOps workflow.

Day-8 | Docker Advanced | Part-2

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