Docker

What is Docker?

Docker is a platform that packages applications along with their dependencies (things they need to run properly) into standardized units called containers.

These containers are isolated from one another and from the host system, ensuring that applications run consistently regardless of the environment they’re in. This way we can make sure that a program can run on both a Windows machine and a Mac.

Simple Analogy

Think of Docker like a lunchbox for your computer programs:

• Traditional Software: Like trying to make a sandwich at school without bringing any ingredients or tools. You’d need to find bread, butter, and fillings at school, and hope they have everything you need!

• Docker Containers: Like having a lunchbox with everything you need for your sandwich - the bread, butter, fillings, and even a knife to spread with. You can take this lunchbox anywhere and make the same sandwich, because everything you need is right there inside it.

Key Concepts

• Containers: Lightweight, standalone packages that contain everything needed to run an application
• Images: Read-only templates used to create containers, similar to a blueprint
• Dockerfile: A text file with instructions for building a Docker image
• Registry: A repository for storing and distributing Docker images (like Docker Hub)
• Docker Compose: A tool for defining and running multi-container applications
• Isolation: Containers are isolated from each other and the host system for security and consistency

Example

# A simple Dockerfile for a Node.js application
FROM node:14-alpine

WORKDIR /app

COPY package*.json ./
RUN npm install

COPY . .

EXPOSE 3000

CMD ["npm", "start"]