Docker Knowledge Base

Quick reference for Docker patterns and PHP-specific guidelines.

Core Concepts

┌─────────────────────────────────────────────────────────────────┐
│                    DOCKER FOR PHP                                │
├─────────────────────────────────────────────────────────────────┤
│                                                                  │
│   Dockerfile         → Build image instructions                  │
│   docker-compose.yml → Multi-container orchestration             │
│   .dockerignore      → Build context exclusions                  │
│   entrypoint.sh      → Container startup logic                   │
│   nginx.conf         → Reverse proxy for PHP-FPM                 │
│   php.ini            → PHP runtime configuration                 │
│   supervisord.conf   → Process management                        │
│                                                                  │
│   Multi-Stage Build:                                             │
│   ┌──────────┐  ┌──────────┐  ┌──────────┐                     │
│   │ composer  │  │ php-ext  │  │production│                     │
│   │  deps     │──│ builder  │──│  final   │                     │
│   └──────────┘  └──────────┘  └──────────┘                     │
│                                                                  │
└─────────────────────────────────────────────────────────────────┘

PHP Docker Image Types

Image	Use Case	Size
php:8.4-fpm-alpine	Production (FPM)	~50MB
php:8.4-cli-alpine	CI/workers	~45MB
php:8.4-fpm	Production (Debian)	~150MB
php:8.4-cli	CI/workers (Debian)	~140MB
php:8.4-apache	Simple deployments	~160MB

Quick Checklists

Dockerfile Checklist

• Multi-stage build (deps → build → production)
• Alpine base image when possible
• Pinned version tags (not latest)
• BuildKit syntax header
• Non-root user
• Health check defined
• .dockerignore present
• Composer deps installed before source copy
• Production PHP config (php.ini-production)
• OPcache enabled and configured
• No secrets in build args or layers

Docker Compose Checklist

• Health checks for all services
• Named volumes for persistent data
• Environment variables via .env file
• Dependency ordering with depends_on + condition
• Resource limits defined
• Networks segmented (frontend/backend)
• No hardcoded passwords

Security Checklist

• Non-root user (USER app)
• Read-only root filesystem where possible
• No secrets in Dockerfile or image
• Minimal base image
• No unnecessary packages
• Capabilities dropped
• No privileged mode

Common Violations Quick Reference

Violation	Where	Severity
FROM php:latest	Dockerfile	High
COPY . . before deps install	Dockerfile	High
Running as root	Dockerfile	High
Secrets in ENV/ARG	Dockerfile	Critical
No health check	Dockerfile/Compose	Medium
No .dockerignore	Project root	Medium
privileged: true	docker-compose.yml	Critical
Hardcoded passwords	docker-compose.yml	Critical
No resource limits	docker-compose.yml	Medium
Missing depends_on conditions	docker-compose.yml	Medium

PHP-Specific Best Practices

Extensions Installation

# Alpine: use apk + docker-php-ext-install
RUN apk add --no-cache libzip-dev icu-dev \
    && docker-php-ext-install zip intl pdo_mysql opcache

# Debian: use apt-get + docker-php-ext-install
RUN apt-get update && apt-get install -y \
    libzip-dev libicu-dev \
    && docker-php-ext-install zip intl pdo_mysql opcache \
    && rm -rf /var/lib/apt/lists/*

OPcache Configuration (Production)

opcache.enable=1
opcache.enable_cli=1
opcache.memory_consumption=256
opcache.interned_strings_buffer=16
opcache.max_accelerated_files=20000
opcache.validate_timestamps=0
opcache.jit=1255
opcache.jit_buffer_size=256M

PHP-FPM Tuning

pm = dynamic
pm.max_children = 50
pm.start_servers = 5
pm.min_spare_servers = 5
pm.max_spare_servers = 35
pm.max_requests = 1000

References

For detailed information, load these reference files:

• references/image-selection.md — Base image comparison and selection guide
• references/multistage-patterns.md — Multi-stage build patterns for PHP
• references/security-hardening.md — Security best practices and hardening
• references/compose-patterns.md — Docker Compose patterns for PHP stacks
• references/production-checklist.md — Production readiness checklist