다단계 빌드와 최적화

멀티 스테이지를 사용하는 이유

스테이지 이름 지정

# Stage 1: dependencies
FROM composer:2 AS vendor
WORKDIR /app
COPY composer.json composer.lock ./
RUN composer install --no-dev --no-scripts --prefer-dist --ignore-platform-reqs

# Stage 2: runtime
FROM php:8.3-fpm-alpine AS runtime
WORKDIR /app
COPY --from=vendor /app/vendor ./vendor
COPY . .

빌드 의존성 분리

FROM php:8.3-fpm-alpine AS ext-builder
ADD https://github.com/mlocati/docker-php-extension-installer/releases/latest/download/install-php-extensions /usr/local/bin/
RUN chmod +x /usr/local/bin/install-php-extensions && \
    install-php-extensions redis igbinary opcache intl

FROM php:8.3-fpm-alpine AS runtime
# Copy compiled extensions + their enable configs
COPY --from=ext-builder /usr/local/lib/php/extensions/ /usr/local/lib/php/extensions/
COPY --from=ext-builder /usr/local/etc/php/conf.d/ /usr/local/etc/php/conf.d/

레이어 캐시 순서

# BAD: copying all source before composer install
# busts the vendor layer on every code change
COPY . .
RUN composer install

# GOOD: lock first, then source
COPY composer.json composer.lock ./
RUN composer install --no-dev --no-autoloader
COPY . .
RUN composer dump-autoload --optimize

BuildKit 캐시 마운트

# syntax=docker/dockerfile:1
FROM composer:2 AS vendor
WORKDIR /app
COPY composer.json composer.lock ./
RUN --mount=type=cache,target=/tmp/composer-cache \
    COMPOSER_CACHE_DIR=/tmp/composer-cache \
    composer install --no-dev --prefer-dist

이미지 크기 측정

# Compare sizes
docker images myapp

# Per-layer contribution
docker history --no-trunc --format '{{.Size}}\t{{.CreatedBy}}' myapp:latest

# Deep inspection of wasted bytes
dive myapp:latest

최종 스테이지 정리

FROM php:8.3-fpm-alpine AS runtime
WORKDIR /app

# bring extensions + vendor in from builders — no Composer here
COPY --from=ext-builder /usr/local/lib/php/extensions/ /usr/local/lib/php/extensions/
COPY --from=ext-builder /usr/local/etc/php/conf.d/ /usr/local/etc/php/conf.d/
COPY --from=vendor /app/vendor ./vendor
COPY . .

USER www-data
CMD ["php-fpm"]

Distroless / Scratch의 한계

# Smallest practical PHP runtime
FROM php:8.3-fpm-alpine

# If musl causes native-lib issues (e.g., some ICU edge cases),
# the glibc Debian slim variant is the safe fallback:
# FROM php:8.3-fpm-bookworm

스테이지 대상 지정

FROM runtime AS dev
ADD https://github.com/mlocati/docker-php-extension-installer/releases/latest/download/install-php-extensions /usr/local/bin/
RUN chmod +x /usr/local/bin/install-php-extensions && \
    install-php-extensions xdebug @composer
USER root
RUN composer install   # includes dev deps

# Build prod:  docker build --target runtime -t app:prod .
# Build dev:   docker build --target dev     -t app:dev  .

레이어 크기 이해하기

<?php
// Simulate layer sizes (MB) for two strategies
$installSteps = [120, 8, 8, 8];

// Separate RUN per step keeps temp files in layers
$separate = array_sum($installSteps);

// Single RUN with cleanup removes temp files before commit
$combined = max($installSteps); // peak, then cleaned

echo "Separate layers total: {$separate} MB\n";
echo "Combined+cleanup:       {$combined} MB\n";
echo 'Saved: ' . ($separate - $combined) . " MB\n";
?>

하나의 RUN에서 설치와 정리 함께 하기

RUN apk add --no-cache --virtual .build-deps $PHPIZE_DEPS && \
    pecl install redis && \
    docker-php-ext-enable redis && \
    apk del .build-deps && \
    rm -rf /tmp/pear /var/cache/apk/*

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