Docker Containers Complete Guide

What is Docker?

Docker packages applications and their dependencies into containers — lightweight, portable units that run identically everywhere. "It works on my machine" becomes "it works everywhere."

Containers vs Virtual Machines

	Container	VM
Size	MBs	GBs
Startup	Seconds	Minutes
OS	Shares host	Full OS each

A Dockerfile

FROM node:20
WORKDIR /app
COPY package.json .
RUN npm install
COPY . .
EXPOSE 3000
CMD ["node", "index.js"]

Essential Commands

docker build -t my-app .       # build image
docker run -p 3000:3000 my-app # run container
docker ps                      # list running
docker stop <id>               # stop
docker images                  # list images

Docker Compose (Multi-Container)

services:
  web:
    build: .
    ports: ["3000:3000"]
  db:
    image: postgres:16

FAQs

Image vs container?

An image is the blueprint; a container is a running instance of it. More in our DevOps guides.

Docker vs Kubernetes?

Docker creates containers; Kubernetes orchestrates many of them at scale.