Docker Cheatsheet

What is Docker?

Docker is a platform that lets you package applications and their dependencies into containers. Containers run consistently across different environments — your laptop, servers, or the cloud.

Images

Images are blueprints for containers. You can pull them from Docker Hub or build your own with a Dockerfile.

docker pull ubuntu
docker images
docker rmi ubuntu

Containers

Containers are running instances of images. You can start, stop, and remove them easily.

docker run ubuntu echo "Hello Docker"
docker ps
docker stop container_id
docker rm container_id

Interactive Mode

Use -it to run containers interactively. --rm automatically removes the container after exit.

docker run -it ubuntu bash
docker run --rm ubuntu echo "Temporary Container"

Ports & Volumes

Expose ports with -p and persist data using -v (volumes).

docker run -p 8080:80 nginx
docker run -v /host/data:/container/data ubuntu

Dockerfile Basics

A Dockerfile defines how to build a custom image. Common commands include FROM, COPY, RUN, CMD, and WORKDIR.

FROM node:18
WORKDIR /app
COPY . .
RUN npm install
CMD ["node", "index.js"]

Build & Run Custom Images

Use docker build to create an image and docker run to start it.

docker build -t myapp .
docker run -p 3000:3000 myapp

Docker Compose

Docker Compose manages multi-container applications with a YAML file. Perfect for apps with databases + backend + frontend.

# docker-compose.yml
version: "3"
services:
  web:
    build: .
    ports:
      - "3000:3000"
  db:
    image: mongo

Logs & Exec

View container logs or open a shell inside a running container.

docker logs container_id
docker exec -it container_id bash

Networks

Networks let containers talk to each other. Docker creates a default bridge, but you can also define custom networks.

docker network ls
docker network create mynetwork
docker run --network=mynetwork myapp

Cleanup

Free up space by removing stopped containers, unused images, and networks with prune commands.

docker system prune
docker volume prune

Best Practices

Use smaller base images (like alpine), add a .dockerignore file to skip unnecessary files, and keep containers single-purpose for efficiency.

How to use this page

1. Start with images and containers basics.
2. Learn Dockerfile and build your own images.
3. Practice Compose for multi-service apps.
4. Explore networks, volumes, and cleanup commands.