Docker Ignore Configuration Skill

This skill provides .dockerignore template and validation logic for optimizing Docker build contexts.

Purpose

Manage .dockerignore configuration to:

• Reduce Docker build context size
• Exclude unnecessary files from Docker builds
• Improve build performance
• Ensure security (exclude .env, credentials)

Usage

This skill is invoked by the dockerignore-agent when:

• Creating new .dockerignore files
• Auditing existing .dockerignore configurations
• Validating .dockerignore against standards

Template

The standard .dockerignore template is located at:

templates/.dockerignore.template

The 5 .dockerignore Standards

Rule 1: Build Artifacts

Must exclude build outputs: dist/, build/, .next/, out/, .turbo/, *.tsbuildinfo, node_modules/

Rule 2: Development Files

Must exclude environment files, IDE configs, OS files, Git files:

• .env* files
• .vscode/, .idea/
• .DS_Store, Thumbs.db
• .git/, .gitignore

Rule 3: CI/CD and Testing

Must exclude CI/CD configs, test files, coverage, documentation:

• .github/, CI config files
• coverage/, *.test.*, *.spec.*, __tests__/, __mocks__/
• docs/, *.md (except README.md)

Rule 4: Logs and Temporary Files

Must exclude logs and temporary files:

• *.log files
• *.tmp, *.temp
• .cache/

Rule 5: Root-Only Placement

Place .dockerignore at the repository root where Docker CLI reads it. Docker uses the build context root for consistent, predictable behavior across all builds.

Benefits of root-only placement:

• Single source of truth for all Docker exclusions
• Patterns apply consistently across the entire build context
• Team members find configuration in the expected location
• Subdirectory patterns work using path prefixes (e.g., apps/web/node_modules/)

Action: Consolidate any subdirectory .dockerignore content into the root file, then remove the nested files.

Validation

To validate a .dockerignore file:

1. Check that the file exists at repository root
2. Read the file content
3. Verify it includes patterns for all 5 rule categories
4. Report any missing categories

Validation Approach

# Check Rule 1: Build artifacts
grep -q "node_modules" .dockerignore && grep -q "dist" .dockerignore

# Check Rule 2: Development files
grep -q ".env" .dockerignore && grep -q ".vscode" .dockerignore

# Check Rule 3: CI/CD and testing
grep -q ".github" .dockerignore && grep -q "coverage" .dockerignore

# Check Rule 4: Logs and temporary
grep -q "*.log" .dockerignore && grep -q "*.tmp" .dockerignore

# Check Rule 5: No nested .dockerignore files
find . -name ".dockerignore" -not -path "./.dockerignore" | wc -l  # Should be 0

Repository Type Considerations

• Consumer Repos: Should strictly follow all 5 standards
• Library Repos: May have intentional differences (e.g., include documentation)

Best Practices

1. Place .dockerignore at repository root only
2. Use template as starting point
3. Include !README.md to explicitly include README in builds
4. Exclude all sensitive files (.env*, credentials)
5. Smaller build context = faster Docker builds
6. Re-audit after making changes

Integration

This skill integrates with:

• Repository type provided via scope parameter. If not provided, use /skill scope-check
• /skill audit-workflow - Bi-directional comparison workflow
• /skill remediation-options - Conform/Update/Ignore choices