Installing Docker Desktop

Docker Desktop is the easiest way to get Docker on macOS. It includes the Docker engine, CLI tools, and a GUI for managing containers.

1. Download Docker Desktop from docker.com/products/docker-desktop
2. Open the .dmg and drag Docker to Applications
3. Launch Docker from Applications
4. Docker needs a moment to start – you'll see the whale icon in your menu bar when it's ready

Or install via Homebrew:

brew install --cask docker

Verify the installation:

docker --version
docker compose version

Running your first container

Pull and run an Nginx web server:

docker run -d -p 8080:80 nginx

This downloads the nginx image from Docker Hub, starts it in the background (-d), and maps port 8080 on your Mac to port 80 inside the container. Open http://localhost:8080 in your browser to see it.

Essential commands

List running containers:

docker ps

List all containers (including stopped):

docker ps -a

Stop a container:

docker stop <container_id>

You only need the first few characters of the ID (e.g., docker stop a1b2).

Remove a stopped container:

docker rm <container_id>

List downloaded images:

docker images

Pull an image without running it:

docker pull postgres

Remove an image:

docker rmi nginx

Docker Hub

Docker Hub (hub.docker.com) hosts thousands of pre-built images. Common ones:

• postgres – PostgreSQL database
• redis – Redis cache/store
• nginx – web server and reverse proxy
• node – Node.js runtime
• python – Python runtime
• mysql – MySQL database

Run a Postgres database:

docker run -d -p 5432:5432 -e POSTGRES_PASSWORD=mysecret postgres

The -e flag sets an environment variable inside the container.

Building your own image

A Dockerfile describes how to build an image. Here's a simple one for a Node.js app:

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

• FROM – base image to start from
• WORKDIR – set the working directory inside the container
• COPY – copy files from your machine into the image
• RUN – run a command during the build (install dependencies)
• CMD – the command to run when the container starts

Build it:

docker build -t my-app .

Run it:

docker run -d -p 3000:3000 my-app

Docker Compose

Docker Compose lets you define and run multiple containers together. Create a docker-compose.yml file:

services:
  web:
    build: .
    ports:
      - "3000:3000"
    depends_on:
      - db
  db:
    image: postgres
    environment:
      POSTGRES_PASSWORD: mysecret
    volumes:
      - pgdata:/var/lib/postgresql/data

volumes:
  pgdata:

Start everything:

docker compose up -d

Stop everything:

docker compose down

Volumes (persist data)

Containers are temporary by default – when you remove a container, its data is gone. Volumes let you persist data:

docker run -d -p 5432:5432 -e POSTGRES_PASSWORD=mysecret -v pgdata:/var/lib/postgresql/data postgres

The -v pgdata:/var/lib/postgresql/data creates a named volume that survives container restarts and removals.

Cleanup

Docker images and stopped containers accumulate over time. Free up space:

docker system prune

This removes stopped containers, unused networks, and dangling images. Add -a to also remove all unused images (not just dangling ones):

docker system prune -a

When NOT to use Docker

• Simple scripts you run once
• Quick one-off tasks
• When your app has no dependencies beyond what's already installed
• Learning a language for the first time (start without the extra complexity)