Test Environment Parity

Also Known As

TL;DR

Explanation

Environment parity (12-Factor App Factor VI): dev, CI, staging, and production use identical PHP version, extensions, database version and configuration, OS, timezone, and locale. Docker Compose committed to the repository ensures all developers use the same stack. PHP version matrix in CI tests against all supported versions. Common divergences that cause bugs: PHP 7.4 vs 8.3 behaviour differences, MySQL strict mode enabled in production but not dev, different timezone configurations.

Common Misconception

Why It Matters

Common Mistakes

• System PHP on developer machines diverging from production version
• No committed docker-compose.yml — each developer's environment drifts over time
• Different MySQL strict mode between environments — queries accepted in dev rejected in production
• Wrong timezone in dev or CI — date calculation bugs that only appear in certain timezones

Code Examples

# Divergent environments — bugs appear only in production:
# Developer: PHP 8.1 (system PHP), MySQL 5.7, UTC timezone
# CI: PHP 8.2 (GitHub Actions default), MySQL 8.0, UTC
# Production: PHP 8.3, MySQL 8.0, Europe/London timezone
# Bug: MySQL 8.0 strict mode rejects query that 5.7 accepts
# Discovered: production deployment — emergency hotfix

# docker-compose.yml committed — identical for all developers:
services:
  php:
    image: php:8.3-fpm-alpine  # Same as production
    environment:
      APP_TIMEZONE: Europe/London  # Match production
  mysql:
    image: mysql:8.0  # Same version as production
    environment:
      MYSQL_STRICT_MODE: '1'  # Match production strict mode

# CI also uses mysql:8.0 and PHP 8.3 — identical stack

References

• ↗ https://12factor.net/dev-prod-parity

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