Docker Layer Efficiency Checker
Analyze Dockerfile layer structure for optimal ordering, cache utilization, and build performance.
Optimal Layer Ordering
| Order | Layer Type | Change Frequency | Example |
|---|---|---|---|
| 1 | Base image | Rare | FROM php:8.4-fpm |
| 2 | System deps | Rare | RUN apt-get install |
| 3 | PHP extensions | Rare | RUN docker-php-ext-install |
| 4 | Composer deps | Weekly | COPY composer.* && composer install |
| 5 | NPM deps | Weekly | COPY package.* && npm ci |
| 6 | Config files | Occasional | COPY php.ini, nginx.conf |
| 7 | App source | Every commit | COPY . /var/www/html |
| 8 | Build steps | Every commit | RUN composer dump-autoload |
Detection Patterns
1. Source Copy Before Dependencies
dockerfile# BAD: Layer 7 before Layer 4 COPY . /var/www/html RUN composer install --no-dev # GOOD: Dependencies first COPY composer.json composer.lock /var/www/html/ RUN composer install --no-dev --no-scripts --no-autoloader COPY . /var/www/html/ RUN composer dump-autoload --optimize
2. Mergeable RUN Commands
dockerfile# BAD: Three layers for related ops RUN apt-get update RUN apt-get install -y libzip-dev RUN rm -rf /var/lib/apt/lists/* # GOOD: Single layer RUN apt-get update && apt-get install -y --no-install-recommends \ libzip-dev && rm -rf /var/lib/apt/lists/*
3. Cache-Busting ARG Placement
dockerfile# BAD: ARG before expensive layers busts cache ARG APP_VERSION=1.0.0 FROM php:8.4-fpm RUN apt-get update && apt-get install -y libzip-dev # GOOD: ARG after expensive layers FROM php:8.4-fpm RUN apt-get update && apt-get install -y libzip-dev ARG APP_VERSION=1.0.0 LABEL version=$APP_VERSION
4. BuildKit Cache Mount Usage
dockerfile# STANDARD: Re-downloads every build RUN composer install --no-dev # OPTIMIZED: BuildKit cache mount RUN --mount=type=cache,target=/root/.composer/cache \ composer install --no-dev --optimize-autoloader # OPTIMIZED: apt cache mount RUN --mount=type=cache,target=/var/cache/apt \ --mount=type=cache,target=/var/lib/apt \ apt-get update && apt-get install -y libzip-dev
5. Config Files Placement
dockerfile# BAD: Config copied early COPY docker/php.ini /usr/local/etc/php/php.ini RUN apt-get update && apt-get install -y libzip-dev # GOOD: Config after system deps, before source RUN apt-get update && apt-get install -y libzip-dev COPY docker/php.ini /usr/local/etc/php/php.ini COPY . /var/www/html/
6. Extension Installation Order
dockerfile# GOOD: All extensions together before app code RUN apt-get update && apt-get install -y --no-install-recommends \ libpng-dev libzip-dev libicu-dev \ && rm -rf /var/lib/apt/lists/* RUN docker-php-ext-install -j$(nproc) gd zip intl opcache pdo_mysql
Grep Patterns
bashGrep: "^(FROM|RUN|COPY|ADD) " --glob "**/Dockerfile*" Grep: "^COPY \\." --glob "**/Dockerfile*" Grep: "--mount=type=cache" --glob "**/Dockerfile*" Grep: "^ARG " --glob "**/Dockerfile*" Grep: "^WORKDIR " --glob "**/Dockerfile*"
Scoring
| Criterion | Weight | Description |
|---|---|---|
| Layer ordering | 30% | Layers in optimal frequency order |
| Mergeable RUN count | 20% | Fewer mergeable pairs = better |
| Cache mount usage | 15% | BuildKit cache for package managers |
| Dependency-first | 20% | Composer/npm files before source |
| Empty layers | 15% | Fewer redundant layers = better |
Score: 0-100% (Excellent > 85 | Good > 70 | Needs Improvement > 50 | Poor <= 50)
Output Format
markdown## Layer Efficiency Report **Score:** X% — [Excellent / Good / Needs Improvement / Poor] **Total Layers:** N **Ordering Violations:** N ### Layer Map | # | Instruction | Category | Order | Status | |---|-------------|----------|-------|--------| | 1 | FROM php:8.4-fpm | Base | 1 | OK | | 2 | COPY . /var/www | Source | 7 | Out of order | ### Issues Found 1. **[Issue]** at line N — [Description and fix] ### Optimization Opportunities - Merge RUN at lines X, Y (saves N layers) - Add BuildKit cache for composer (saves ~30s) - Reorder COPY instructions (improves cache hit rate)
