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Docker and Containers

Docker is a tool that packages applications into lightweight, independent containers, allowing them to run consistently anywhere.

1. Why Docker?​

  • Environment Consistency: Solves the "It works on my machine" problem. Perfectly aligns development, testing, and production environments.
  • Isolation: Safely run apps using different library versions on a single server.
  • Deployment Speed: Use images to skip infrastructure configuration and launch apps immediately.

2. Core Docker Concepts​

  • Image: A template including executable files, libraries, settings, etc.
  • Container: The running state of an image.
  • Dockerfile: A specification for creating an image.

3. Dockerfile Example​

# Set base image
FROM node:18

# Set working directory
WORKDIR /app

# Install dependencies
COPY package*.json ./
RUN npm install

# Copy source and execute
COPY . .
CMD ["npm", "start"]

4. Essential Commands​

docker build -t my-app .  # Build an image
docker run -p 8080:80 my-app # Run a container (port binding)
docker ps                 # Check running containers
docker stop [ID]          # Stop a container

In the next section, we'll learn about CI/CD, which automatically detects code changes and deploys them.

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