Docker Fundamentals

Docker is a platform for building, shipping, and running applications in containers.

What is a Container?

A container is a lightweight, standalone, executable package that includes everything needed to run an application: code, runtime, system tools, libraries, and settings.

Key Concepts

• Image — a read-only template used to create containers
• Container — a running instance of an image
• Dockerfile — a text file with instructions to build an image
• Volume — persistent storage mounted into a container
• Network — how containers communicate with each other

Basic Commands

# Pull an image
docker pull node:22-alpine

# Run a container
docker run -p 3000:3000 node:22-alpine

# List running containers
docker ps

# Build an image from a Dockerfile
docker build -t my-app .

# Stop a container
docker stop <container-id>

Example Dockerfile

FROM node:22-alpine
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["node", "index.js"]