Docker and Docker Composer

Docker Overview

Docker is a powerful platform for developing, shipping, and running applications inside lightweight containers. Containers package an application and its dependencies, ensuring consistency across development, testing, and production environments.

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Key Concepts

• Image: A read-only template with the application and its dependencies.
• Container: A runnable instance of an image.
• Dockerfile: A script defining the instructions to create a Docker image.
• Docker Compose: A tool to define and manage multi-container Docker applications using a docker-compose.yml file.

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Basic Docker Commands

1. Pull an Image

The docker pull <image-name>:<tag> command downloads (or “pulls”) a Docker image from a registry like Docker Hub to your local machine.

Example:

docker pull nginx:latest

This pulls the latest NGINX image from Docker Hub. After downloading, you can use this image to create containers.

Other Examples:

docker pull python:3.10  # Python 3.10
docker pull ubuntu:20.04  # Ubuntu 20.04
docker pull redis:6.2  # Redis 6.2

Using tags ensures your containers use specific, consistent versions across different environments.

2. Run a Container

docker run -d --name <container-name> <image-name>

Example:

docker run -d --name my_nginx nginx

This runs a new container named my_nginx in detached mode (-d) using the NGINX image.

3. Other Basic Commands

• List running containers: docker ps
• Stop a container: docker stop <container-id>
• Remove a container: docker rm <container-id>
• List images: docker images
• Remove an image: docker rmi <image-id>

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Dockerfile Basics

A Dockerfile is a file with instructions for building a Docker image.

Example Dockerfile:

# Use an official Node.js image as the base
FROM node:14

# Set the working directory in the container
WORKDIR /app

# Copy package.json and install dependencies
COPY package*.json ./
RUN npm install

# Copy the rest of the application code
COPY . .

# Expose port 3000
EXPOSE 3000

# Start the application
CMD ["npm", "start"]

To build an image from this Dockerfile:

docker build -t <image-name> .

Example:

docker build -t mynodeapp .

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Docker Compose

Docker Compose simplifies managing multi-container applications with a single YAML configuration file.

Example docker-compose.yml:

version: '3.8'
services:
  web:
    image: nginx:latest
    ports:
      - "80:80"

  app:
    build: .
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=development
    volumes:
      - .:/app
    depends_on:
      - db

  db:
    image: postgres:13
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: password
      POSTGRES_DB: mydatabase
    ports:
      - "5432:5432"

Common Docker Compose Commands:

• Build and Start Services: docker-compose up --build
• Start Services in Detached Mode: docker-compose up -d
• Stop Services: docker-compose down
• View Logs: docker-compose logs -f
• Rebuild and Restart a Service: docker-compose up -d --build <service-name>

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Summary of Key Docker and Docker Compose Commands

Command	Description
docker build -t <image_name> .	Build an image from a Dockerfile
docker run -d --name <name> <image>	Run a container from an image
docker ps	List running containers
docker stop <container_id>	Stop a running container
docker exec -it <name> /bin/bash	Open a shell in a running container
docker-compose up -d	Start services defined in a Compose file
docker-compose down	Stop services and remove containers
docker-compose ps	List services in a Compose setup

Docker and Docker Compose streamline application deployment through containerization, ensuring consistent and efficient application environments across various stages of development.

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About Docker Hub

Docker Hub is a cloud-based registry where users can store, share, and discover container images, often called the “GitHub for Docker images.”

Key Features:

• Image Repository: A central place to store public or private Docker images.
• Official Images: Trusted, verified images for popular software (e.g., NGINX, MySQL), maintained by publishers.
• Community Images: A vast library of images contributed by the community.
• Automated Builds: Automatically build images from source repositories like GitHub.
• Image Tags: Specify and manage versions of an image for consistency.

Docker Hub Commands:

• Login: docker login
• Pull an Image: docker pull <repository>/<image>:<tag>

• Push an Image:

  docker tag <local-image-name> <username>/<repository>:<tag>
  docker push <username>/<repository>:<tag>
  

• Search for an Image: docker search <image-name>

Best Practices:

• Use Official Images when possible, as they are secure and well-maintained.
• Set Up Automated Builds: Connect Docker Hub with a Git repository to automate image updates.
• Use Tags to manage versions and ensure consistent deployment.

Free TryHackMe Rooms

• Intro to Docker

• Intro to Containerisation

Docker docs