docker-platform-guide

🚨 CRITICAL GUIDELINES

Windows File Path Requirements

MANDATORY: Always Use Backslashes on Windows for File Paths

When using Edit or Write tools on Windows, you MUST use backslashes (\) in file paths, NOT forward slashes (/).

Examples:

• ❌ WRONG: D:/repos/project/file.tsx
• ✅ CORRECT: D:\repos\project\file.tsx

This applies to:

• Edit tool file_path parameter
• Write tool file_path parameter
• All file operations on Windows systems

Documentation Guidelines

NEVER create new documentation files unless explicitly requested by the user.

• Priority: Update existing README.md files rather than creating new documentation
• Repository cleanliness: Keep repository root clean - only README.md unless user requests otherwise
• Style: Documentation should be concise, direct, and professional - avoid AI-generated tone
• User preference: Only create additional .md files when user specifically asks for documentation

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Docker Platform-Specific Guide

This skill provides detailed guidance on Docker differences, considerations, and optimizations for Windows, Linux, and macOS platforms.

Linux

Advantages

• Native containers: No virtualization layer overhead
• Best performance: Direct kernel features (cgroups, namespaces)
• Full feature set: All Docker features available
• Production standard: Most production deployments run on Linux
• Flexibility: Multiple distributions supported

Platform Features

Container Technologies:

• Namespaces: PID, network, IPC, mount, UTS, user
• cgroups v1 and v2 for resource control
• Overlay2 storage driver (recommended)
• SELinux and AppArmor for mandatory access control

Storage Drivers:

# Check current driver
docker info | grep "Storage Driver"

# Recommended: overlay2
# /etc/docker/daemon.json
{
  "storage-driver": "overlay2"
}

Linux-Specific Configuration

Daemon Configuration (/etc/docker/daemon.json):

{
  "storage-driver": "overlay2",
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "10m",
    "max-file": "3"
  },
  "live-restore": true,
  "userland-proxy": false,
  "userns-remap": "default",
  "icc": false,
  "default-ulimits": {
    "nofile": {
      "Name": "nofile",
      "Hard": 64000,
      "Soft": 64000
    }
  }
}

User Namespace Remapping:

# Enable in daemon.json
{
  "userns-remap": "default"
}

# Restart Docker
sudo systemctl restart docker

# Result: root in container = unprivileged user on host

SELinux Integration

# Check SELinux status
sestatus

# Run container with SELinux enabled
docker run --security-opt label=type:svirt_sandbox_file_t myimage

# Volume labels
docker run -v /host/path:/container/path:z myimage  # Private label
docker run -v /host/path:/container/path:Z myimage  # Shared label

AppArmor Integration

# Check AppArmor status
sudo aa-status

# Run with default Docker profile
docker run --security-opt apparmor=docker-default myimage

# Create custom profile
sudo aa-genprof docker run myimage

Systemd Integration

# Check Docker service status
sudo systemctl status docker

# Enable on boot
sudo systemctl enable docker

# Restart Docker
sudo systemctl restart docker

# View logs
sudo journalctl -u docker -f

# Configure service
sudo systemctl edit docker

cgroup v1 vs v2

# Check cgroup version
stat -fc %T /sys/fs/cgroup/

# If using cgroup v2, ensure Docker version >= 20.10

# /etc/docker/daemon.json
{
  "exec-opts": ["native.cgroupdriver=systemd"]
}

Linux Distribution Specifics

Ubuntu/Debian:

# Install Docker
sudo apt-get update
sudo apt-get install 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
sudo chmod a+r /etc/apt/keyrings/docker.asc

echo \
  "deb [arch=$(dpkg --print-architecture) 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 > /dev/null

sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io

# Non-root user
sudo usermod -aG docker $USER

RHEL/CentOS/Fedora:

# Install Docker
sudo dnf -y install dnf-plugins-core
sudo dnf config-manager --add-repo https://download.docker.com/linux/fedora/docker-ce.repo
sudo dnf install docker-ce docker-ce-cli containerd.io

# Start Docker
sudo systemctl start docker
sudo systemctl enable docker

# Non-root user
sudo usermod -aG docker $USER

Alpine:

# Install Docker
apk add docker docker-compose

# Start Docker
rc-update add docker boot
service docker start

macOS

Architecture

• Docker Desktop: Required (no native Docker on macOS)
• Virtualization: Uses HyperKit (Intel) or Virtualization.framework (Apple Silicon)
• Linux VM: Containers run in lightweight Linux VM
• File sharing: osxfs or VirtioFS for bind mounts

macOS-Specific Considerations

Resource Allocation:

Docker Desktop → Preferences → Resources → Advanced
- CPUs: Allocate based on workload (default: half available)
- Memory: Allocate generously (default: 2GB, recommend 4-8GB)
- Swap: 1GB minimum
- Disk image size: 60GB+ for development

File Sharing Performance:

Traditional osxfs is slow. Improvements:

1. VirtioFS: Enable in Docker Desktop settings (faster)
2. Delegated/Cached mounts:

volumes:
  # Host writes delayed (best for source code)
  - ./src:/app/src:delegated

  # Container writes cached (best for build outputs)
  - ./build:/app/build:cached

  # Default consistency (slowest but safest)
  - ./data:/app/data:consistent

Network Access:

# Access host from container
host.docker.internal

# Example: Connect to host PostgreSQL
docker run -e DATABASE_URL=postgresql://host.docker.internal:5432/db myapp

Apple Silicon (M1/M2/M3) Specifics

Architecture Considerations:

# Check image architecture
docker image inspect node:20-alpine | grep Architecture

# M-series Macs are ARM64
# Some images only available for AMD64

# Build multi-platform
docker buildx build --platform linux/amd64,linux/arm64 -t myapp .

# Run AMD64 image on ARM (via emulation)
docker run --platform linux/amd64 myimage  # Slower

Rosetta 2 Integration:

Docker Desktop → Features in development → Use Rosetta for x86/amd64 emulation

Faster AMD64 emulation on Apple Silicon.

macOS Docker Desktop Settings

General:

• ✅ Start Docker Desktop when you log in
• ✅ Use VirtioFS (better performance)
• ✅ Use Virtualization framework (Apple Silicon)

Resources:

CPUs: 4-6 (for development)
Memory: 6-8 GB (for development)
Swap: 1-2 GB
Disk image size: 100+ GB (grows dynamically)

Docker Engine:

{
  "builder": {
    "gc": {
      "enabled": true,
      "defaultKeepStorage": "20GB"
    }
  },
  "experimental": false,
  "features": {
    "buildkit": true
  }
}

macOS File Permissions

# macOS user ID and group ID
id -u  # Usually 501
id -g  # Usually 20

# Match in container
docker run --user 501:20 myimage

# Or in Dockerfile
RUN adduser -u 501 -g 20 appuser
USER appuser

macOS Development Workflow

# docker-compose.yml for development
version: '3.8'

services:
  app:
    build: .
    volumes:
      # Source code with delegated (better performance)
      - ./src:/app/src:delegated
      # node_modules in volume (much faster than bind mount)
      - node_modules:/app/node_modules
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=development

volumes:
  node_modules:

Common macOS Issues

Problem: Slow file sync Solution:

• Use VirtioFS
• Use delegated/cached mounts
• Store dependencies in volumes (not bind mounts)

Problem: High CPU usage Solution:

• Reduce file watching
• Exclude large directories from file sharing
• Allocate more resources

Problem: Port already in use Solution:

# Find process using port
lsof -i :PORT
kill -9 PID

Windows

Windows Container Types

1. Linux Containers on Windows (LCOW):

• Most common for development
• Uses WSL2 or Hyper-V backend
• Runs Linux containers
• Good compatibility

2. Windows Containers:

• Native Windows containers
• For Windows-specific workloads
• Requires Windows Server base images
• Less common in development

Windows Backend Options

WSL2 Backend (Recommended):

• Faster
• Better resource usage
• Native Linux kernel
• Requires Windows 10/11 (recent versions)

Hyper-V Backend:

• Older option
• More resource intensive
• Works on older Windows versions

WSL2 Configuration

Enable WSL2:

# Run as Administrator
wsl --install

# Or manually
dism.exe /online /enable-feature /featurename:Microsoft-Windows-Subsystem-Linux /all /norestart
dism.exe /online /enable-feature /featurename:VirtualMachinePlatform /all /norestart

# Set WSL2 as default
wsl --set-default-version 2

# Install Ubuntu (or other distro)
wsl --install -d Ubuntu

Docker Desktop Integration:

Settings → Resources → WSL Integration
- Enable integration with default distro
- Select additional distros

Windows Path Considerations

Path Formats:

# Forward slashes (recommended, works everywhere)
docker run -v C:/Users/name/project:/app myimage

# Backslashes (need escaping in some contexts)
docker run -v C:\Users\name\project:/app myimage

# In docker-compose.yml (forward slashes)
volumes:
  - C:/Users/name/project:/app

# Or relative paths
volumes:
  - ./src:/app/src

Git Bash / MINGW Path Conversion Issues

CRITICAL ISSUE: When using Docker in Git Bash (MINGW) on Windows, automatic path conversion breaks volume mounts.

The Problem:

# What you type in Git Bash:
docker run -v $(pwd):/app myimage

# What Git Bash converts it to (BROKEN):
docker run -v C:\Program Files\Git\d\repos\project:/app myimage

Solutions:

1. MSYS_NO_PATHCONV (Recommended):

# Per-command fix
MSYS_NO_PATHCONV=1 docker run -v $(pwd):/app myimage

# Session-wide fix (add to ~/.bashrc)
export MSYS_NO_PATHCONV=1

# Function wrapper (automatic for all Docker commands)
docker() {
  (export MSYS_NO_PATHCONV=1; command docker.exe "$@")
}
export -f docker

2. Double Slash Workaround:

# Use double leading slash to prevent conversion
docker run -v //c/Users/project:/app myimage

# Works with $(pwd) too
docker run -v //$(pwd):/app myimage

3. Named Volumes (No Path Issues):

# Named volumes work without any fixes
docker run -v my-data:/data myimage

What Works Without Modification:

• Docker Compose YAML files with relative paths
• Named volumes
• Network and image commands
• Container commands without volumes

What Needs MSYS_NO_PATHCONV:

• Bind mounts with $(pwd)
• Bind mounts with absolute Unix-style paths
• Volume mounts specified on command line

Shell Detection:

# Detect Git Bash/MINGW and auto-configure
if [ -n "$MSYSTEM" ] || [[ "$(uname -s)" == MINGW* ]]; then
  export MSYS_NO_PATHCONV=1
  echo "Git Bash detected - Docker path conversion fix enabled"
fi

Recommended ~/.bashrc Configuration:

# Docker on Git Bash fix
if [ -n "$MSYSTEM" ]; then
  export MSYS_NO_PATHCONV=1
fi

See the docker-git-bash-guide skill for comprehensive path conversion documentation, troubleshooting, and examples.

Windows File Sharing

Configure Shared Drives:

Docker Desktop → Settings → Resources → File Sharing
Add: C:\, D:\, etc.

Performance Considerations:

• File sharing is slower than Linux/Mac
• Use WSL2 backend for better performance
• Store frequently accessed files in WSL2 filesystem

Windows Line Endings

Problem: CRLF vs LF line endings

Solution:

# Git configuration
git config --global core.autocrlf input

# Or per-repo (.gitattributes)
* text=auto
*.sh text eol=lf
*.bat text eol=crlf

# In Dockerfile for scripts
FROM alpine
COPY --chmod=755 script.sh /
# Ensure LF endings
RUN dos2unix /script.sh || sed -i 's/\r$//' /script.sh

Windows Firewall

# Allow Docker Desktop
New-NetFirewallRule -DisplayName "Docker Desktop" -Direction Inbound -Program "C:\Program Files\Docker\Docker\Docker Desktop.exe" -Action Allow

# Check blocked ports
netstat -ano | findstr :PORT

Windows-Specific Docker Commands

# Run PowerShell in container
docker run -it mcr.microsoft.com/powershell:lts-7.4-windowsservercore-ltsc2022

# Windows container example
docker run -it mcr.microsoft.com/windows/servercore:ltsc2022 cmd

# Check container type
docker info | Select-String "OSType"

WSL2 Disk Management

Problem: WSL2 VHDX grows but doesn't shrink

Solution:

# Stop Docker Desktop and WSL
wsl --shutdown

# Compact disk image (run as Administrator)
# Method 1: Optimize-VHD (requires Hyper-V tools)
Optimize-VHD -Path "$env:LOCALAPPDATA\Docker\wsl\data\ext4.vhdx" -Mode Full

# Method 2: diskpart
diskpart
# In diskpart:
select vdisk file="C:\Users\YourName\AppData\Local\Docker\wsl\data\ext4.vhdx"
attach vdisk readonly
compact vdisk
detach vdisk
exit

Windows Development Workflow

# docker-compose.yml for Windows
version: '3.8'

services:
  app:
    build: .
    volumes:
      # Use forward slashes
      - ./src:/app/src
      # Named volumes for better performance
      - node_modules:/app/node_modules
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=development
    # Windows-specific: ensure proper line endings
    command: sh -c "dos2unix /app/scripts/*.sh && npm start"

volumes:
  node_modules:

Common Windows Issues

Problem: Permission denied errors Solution:

# Run Docker Desktop as Administrator
# Or grant permissions to Docker Desktop
icacls "C:\ProgramData\DockerDesktop" /grant Users:F /T

Problem: Slow performance Solution:

• Use WSL2 backend
• Store project in WSL2 filesystem (\\wsl$\Ubuntu\home\user\project)
• Use named volumes for node_modules, etc.

Problem: Path not found Solution:

• Use forward slashes
• Ensure drive is shared in Docker Desktop
• Use absolute paths or ${PWD}

Platform Comparison

Feature	Linux	macOS	Windows
Performance	Excellent (native)	Good (VM overhead)	Good (WSL2) to Fair (Hyper-V)
File sharing	Native	Slow (improving with VirtioFS)	Slow (better in WSL2)
Resource efficiency	Best	Good	Good (WSL2)
Feature set	Complete	Complete	Complete (LCOW)
Production	Standard	Dev only	Dev only (LCOW)
Ease of use	Moderate	Easy (Docker Desktop)	Easy (Docker Desktop)
Cost	Free	Free (Docker Desktop Personal)	Free (Docker Desktop Personal)

Cross-Platform Best Practices

Multi-Platform Images

# Create buildx builder
docker buildx create --name multiplatform --driver docker-container --use

# Build for multiple platforms
docker buildx build \
  --platform linux/amd64,linux/arm64,linux/arm/v7 \
  -t myimage:latest \
  --push \
  .

Platform-Agnostic Dockerfiles

# Works on all platforms
FROM node:20-alpine

# Use COPY with --chmod (not RUN chmod, which is slower)
COPY --chmod=755 script.sh /usr/local/bin/

# Use environment variables for paths
ENV APP_HOME=/app
WORKDIR ${APP_HOME}

# Use exec form for CMD/ENTRYPOINT (works on Windows containers too)
CMD ["node", "server.js"]

Cross-Platform Compose Files

version: '3.8'

services:
  app:
    build: .
    volumes:
      # Relative paths work everywhere
      - ./src:/app/src
      # Named volumes (platform-agnostic)
      - data:/app/data
    environment:
      # Use environment variables
      - NODE_ENV=${NODE_ENV:-development}

volumes:
  data:

Testing Across Platforms

# Test on different platforms with buildx
docker buildx build --platform linux/amd64 -t myapp:amd64 --load .
docker run --rm myapp:amd64

docker buildx build --platform linux/arm64 -t myapp:arm64 --load .
docker run --rm myapp:arm64

Platform Selection Guide

Choose Linux for:

• Production deployments
• Maximum performance
• Full Docker feature set
• Minimal overhead
• CI/CD pipelines

Choose macOS for:

• Development on Mac hardware
• When you need macOS tools
• Docker Desktop ease of use
• M1/M2/M3 development

Choose Windows for:

• Development on Windows hardware
• Windows-specific applications
• When team uses Windows
• WSL2 for better Linux container support

This platform guide covers the major differences. Always test on your target deployment platform before going to production.