Docker Fundamentals

What is Docker?

Docker is an open-source platform that automates the deployment, scaling, and management of applications using containerization technology. Containers allow developers to package an application with all its dependencies into a standardized unit for software development.

Unlike virtual machines, containers share the host system's kernel, making them lightweight and fast. This means you can run many more containers on a given hardware combination than virtual machines.

Docker Architecture

Docker uses a client-server architecture with the following key components:

• Docker Daemon - The background service running on the host that manages building, running, and distributing Docker containers
• Docker Client - The command-line tool that allows users to interact with the Docker daemon
• Docker Registry - A storage and distribution system for Docker images (Docker Hub is the default public registry)
• Docker Images - Read-only templates used to create containers
• Docker Containers - Running instances of Docker images

Key Docker Concepts

Images vs Containers

A Docker image is like a blueprint or template - it contains everything needed to run an application (code, runtime, libraries, environment variables, config files). A container is a running instance of an image. You can run multiple containers from the same image.

Dockerfile

A Dockerfile is a text document containing instructions to build a Docker image. Each instruction creates a layer in the image, making it efficient to rebuild images when only specific parts change.

Docker Compose

Docker Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application's services, networks, and volumes.

Benefits of Docker

• 🚀 Consistency - Same environment from development to production
• ⚡ Speed - Containers start in seconds, not minutes
• 📦 Portability - Run anywhere Docker is installed
• 🔧 Isolation - Each container is isolated from others
• 💰 Efficiency - Better resource utilization than VMs
• 🔄 Scalability - Easy horizontal scaling

Docker Best Practices

• Use official base images when possible
• Keep images small by using multi-stage builds
• Don't run processes as root inside containers
• Use .dockerignore to exclude unnecessary files
• Tag images with meaningful version numbers
• Scan images for security vulnerabilities

# Pull an image from Docker Hub
docker pull nginx:latest

# List all images
docker images

# Run a container
docker run -d -p 8080:80 --name my-nginx nginx:latest

# List running containers
docker ps

# Stop a container
docker stop my-nginx

# Remove a container
docker rm my-nginx

# Remove an image
docker rmi nginx:latest

# Use an official Python runtime as base
FROM python:3.11-slim

# Set environment variables
ENV PYTHONDONTWRITEBYTECODE=1
ENV PYTHONUNBUFFERED=1

# Set work directory
WORKDIR /app

# Install dependencies
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Copy project
COPY . .

# Expose port
EXPOSE 8000

# Run the application
CMD ["python", "manage.py", "runserver", "0.0.0.0:8000"]