Install Docker Desktop

# ===== macOS =====
# Docker Desktop (commercial license for companies > 250 / USD 10M):
brew install --cask docker
open /Applications/Docker.app

# Free alternatives:
# Colima — Linux VM + Docker CLI, lightweight
brew install colima docker
colima start

# Rancher Desktop — Docker or containerd backends, free
brew install --cask rancher-desktop

# ===== Linux (Ubuntu / Debian) =====
sudo apt update
sudo apt install -y ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
echo "deb [signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu \
$(. /etc/os-release && echo "$VERSION_CODENAME") stable" | sudo tee /etc/apt/sources.list.d/docker.list
sudo apt update
sudo apt install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

# Add yourself to the docker group (logout/login after):
sudo usermod -aG docker $USER

# Fedora / RHEL: sudo dnf install -y docker-ce
# Arch: sudo pacman -S docker

# ===== Windows =====
# Docker Desktop (with WSL 2 backend):
winget install Docker.DockerDesktop
# Requires WSL 2; the installer walks you through enabling it.

# ===== Verify =====
docker --version
docker compose version
docker run --rm hello-world

# ===== Post-install niceties =====
# Auto-start: most installers do this
# Configure resource limits (Desktop: Settings -> Resources)
# Enable BuildKit (default in modern Docker): faster builds

# ===== Login to registries =====
docker login                           # Docker Hub
docker login ghcr.io -u <github-user>  # GitHub Container Registry
docker login 1234.dkr.ecr.region.amazonaws.com   # ECR (use aws ecr get-login-password)

# ===== Pull + run =====
docker pull nginx:1.27-alpine
docker run --rm -p 8080:80 nginx:1.27-alpine
# http://localhost:8080

# ===== Build a small image =====
mkdir hello && cd hello
cat > Dockerfile <<'EOF'
FROM nginx:1.27-alpine
COPY index.html /usr/share/nginx/html/index.html
EOF
echo '<h1>hi</h1>' > index.html
docker build -t hello-nginx .
docker run --rm -p 8080:80 hello-nginx

# ===== Cleanup =====
docker ps          # running
docker ps -a       # all (incl stopped)
docker images
docker system df   # disk usage
docker system prune -a   # remove unused images / containers / volumes

# ===== Patterns to internalise =====
# - Add your user to the docker group on Linux (no sudo)
# - Use BuildKit (default) for faster builds
# - Pull base images by digest in prod
# - Set resource limits explicitly on Desktop

# ===== Pitfalls =====
# - Forgetting to logout/login after groupadd -> permission denied
# - Docker Desktop EULA on companies > 250 employees
# - Pulling 'latest' tags -> non-reproducible builds
# - Mounting your home dir into a container without thought (leaks)

# macOS / Windows — Docker Desktop
# Linux — install Docker Engine (apt / dnf)
docker --version