Docker - Self-Hosted Applications

What is Docker?

Docker is a platform for developing, shipping, and running applications in containers. Containers are lightweight and contain everything needed to run the software.

💡 Key Benefit: Docker allows you to package an application with all of its dependencies into a standardized unit for software development.

Installing Docker

On Ubuntu/Debian:

                # Update package index
sudo apt update

# Install dependencies
sudo apt install -y apt-transport-https ca-certificates curl software-properties-common

# Add Docker GPG key
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

# Add Docker repository
echo "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

# Install Docker
sudo apt update
sudo apt install -y docker-ce docker-ce-cli containerd.io

# Start and enable Docker
sudo systemctl start docker
sudo systemctl enable docker
            

Essential Docker Commands

🔍 Check Docker Version

docker --version

Display the Docker version information

📋 List Containers

docker ps -a

Show all containers (running and stopped)

🖼️ List Images

docker images

Show all Docker images on your system

▶️ Run a Container

docker run -d nginx

Run nginx container in detached mode

🛑 Stop Container

docker stop container_id

Stop a running container

🗑️ Remove Container

docker rm container_id

Remove a stopped container

📥 Pull Image

docker pull ubuntu:latest

Download an image from Docker Hub

🔨 Build Image

docker build -t myapp .

Build an image from Dockerfile

🌐 Map Ports

docker run -p 8080:80 nginx

Map container port 80 to host port 8080

📁 Mount Volume

docker run -v /data:/data nginx

Mount host directory to container

📝 View Logs

docker logs container_id

View logs from a container

🔄 Restart Container

docker restart container_id

Restart a container

Creating a Dockerfile

A Dockerfile is a script that contains instructions to build a Docker image.

                # Use official Node.js image as base
FROM node:18-alpine

# Set working directory
WORKDIR /app

# Copy package files
COPY package*.json ./

# Install dependencies
RUN npm install

# Copy application files
COPY . .

# Expose port
EXPOSE 3000

# Define startup command
CMD ["node", "index.js"]
            

Dockerfile Instructions:

FROM - Base image to start from
WORKDIR - Set working directory
COPY - Copy files to container
RUN - Execute commands during build
EXPOSE - Document the port
CMD - Default command to run
ENV - Set environment variables

Docker Compose

Docker Compose is a tool for defining and running multi-container Docker applications.

                version: '3.8'
services:
  web:
    build: .
    ports:
      - "3000:3000"
    volumes:
      - .:/app"
    environment:
      - NODE_ENV=development"

  redis:
    image: "redis:alpine"
    ports:
      - "6379:6379"
            

Docker Compose Commands:

docker-compose up -d - Start all services
docker-compose down - Stop all services
docker-compose ps - List services
docker-compose logs -f - View logs
docker-compose restart - Restart services

Common Docker Use Cases

Running a Web Server (Nginx)

                # Run nginx with port mapping and volume mount
docker run -d -p 8080:80 --name mynginx -v /var/www/html:/usr/share/nginx/html nginx
            

Running a Database (PostgreSQL)

                # Run PostgreSQL with environment variables
docker run -d --name postgres -e POSTGRES_PASSWORD=secret -e POSTGRES_DB=mydb -p 5432:5432 postgres
            

Running a Ghost Blog

                # Run Ghost CMS
docker run -d --name ghost -p 2368:2368 -v ghost content:/var/lib/ghost/content ghost
            

💡 Pro Tip: Always use -d flag to run containers in detached mode (background). Use docker logs -f container_name to view logs.

🐳 Docker Basics