dykyi-roman 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
# 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
# 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
# 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=$APP_VERSION
4. BuildKit Cache Mount Usage
# STANDARD: Re-downloads every build
RUN composer install --no-dev
# OPTIMIZED: BuildKit cache mount
RUN --mount=type=cache,target=/root/.composer/cache \
composer install --no-dev --optimize-autoloader
# OPTIMIZED: apt cache mount
RUN --mount=type=cache,target=/var/cache/apt \
--mount=type=cache,target=/var/lib/apt \
apt-get update && apt-get install -y libzip-dev
5. Config Files Placement
# BAD: Config copied early
COPY docker/php.ini /usr/local/etc/php/php.ini
RUN apt-get update && apt-get install -y libzip-dev
# GOOD: Config after system deps, before source
RUN apt-get update && apt-get install -y libzip-dev
COPY docker/php.ini /usr/local/etc/php/php.ini
COPY . /var/www/html/
6. Extension Installation Order
# GOOD: All extensions together before app code
RUN apt-get update && apt-get install -y --no-install-recommends \
libpng-dev libzip-dev libicu-dev \
&& rm -rf /var/lib/apt/lists/*
RUN docker-php-ext-install -j$(nproc) gd zip intl opcache pdo_mysql
Grep Patterns
Grep: "^(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
## 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)