Docker Cheat Sheet

Docker is a tool that lets you package applications into containers: lightweight, portable environments that include everything needed to run your app.

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Basic Concepts

Concept	Meaning
Image	Blueprint (read-only template)
Container	Running instance of an image
Dockerfile	Instructions to build an image
Volume	Persistent storage
Network	Communication between containers

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Images

Pull an image

docker pull nginx

List images

docker images

Remove image

docker rmi nginx

Build image from Dockerfile

docker build -t my-app .

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Containers

Run a container

docker run nginx

Run in background (detached)

docker run -d nginx

Name a container

docker run --name web nginx

Map ports

docker run -p 8080:80 nginx

(host:container)

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List containers

docker ps        # running
docker ps -a     # all

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Stop / start / restart

docker stop container_id
docker start container_id
docker restart container_id

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Remove container

docker rm container_id

Force remove running container:

docker rm -f container_id

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Execute inside container

docker exec -it container_id bash

or:

docker exec -it container_id sh

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Logs & Inspection

View logs

docker logs container_id

Follow logs live:

docker logs -f container_id

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Inspect container

docker inspect container_id

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Dockerfile Basics

Example:

FROM node:18
 
WORKDIR /app
 
COPY package*.json ./
RUN npm install
 
COPY . .
 
EXPOSE 3000
 
CMD ["npm", "start"]

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Build from Dockerfile

docker build -t my-node-app .

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Volumes

Create volume

docker volume create mydata

Run with volume

docker run -v mydata:/data nginx

Bind mount (local folder)

docker run -v $(pwd):/app nginx

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Networks

List networks

docker network ls

Create network

docker network create mynet

Run container in network

docker run --network mynet nginx

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Docker Compose (multi-container)

Example file

version: "3.9"
 
services:
  app:
    build: .
    ports:
      - "3000:3000"
    volumes:
      - .:/app
 
  db:
    image: postgres
    environment:
      POSTGRES_PASSWORD: example

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Commands

Start services:

docker compose up

Detached mode:

docker compose up -d

Stop services:

docker compose down

Rebuild:

docker compose up --build

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Cleanup

Remove unused containers

docker container prune

Remove unused images

docker image prune

Full system cleanup (dangerous)

docker system prune -a

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Debugging

View resource usage

docker stats

Check disk usage

docker system df

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Useful Shortcuts

docker ps -a          # all containers
docker images         # all images
docker exec -it       # enter container
docker logs -f        # live logs
docker stop $(docker ps -q)
docker rm $(docker ps -aq)

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Port Mapping Mental Model

Host Machine        Container
------------        ----------
localhost:8080  →   80 (nginx)
localhost:3000  →   3000 (node)

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Key Idea

Docker isolates applications like:

“Run everything as if it has its own computer”

But:

• shares kernel

• stays lightweight

• runs anywhere

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Most Used Commands

docker pull
docker run
docker ps
docker stop
docker rm
docker build
docker exec
docker logs
docker compose up
docker compose down

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Golden Workflow

docker build -t my-app .
 
docker run -p 3000:3000 my-app
 
docker ps
 
docker logs -f container_id
 
docker stop container_id

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