Symfony consistently separates configuration from code – a central principle we'll understand in this chapter, before setting up our task manager's database connection in chapter 5.

The three standard environments

The APP_ENV variable determines which environment is active – dev by default when working locally with the Symfony CLI.

Understanding .env files

Symfony reads environment variables from SEVERAL .env* files, which override each other in a precisely defined order:

1. .env – default values, gets VERSION-CONTROLLED (no real secrets!).
2. .env.local – local overrides, NOT version-controlled, for your personal values.
3. .env.$APP_ENV (e.g. .env.test) – environment-specific, version-controlled.
4. .env.$APP_ENV.local – local, environment-specific override, NOT version-controlled.

APP_ENV=dev
APP_SECRET=change_me_in_env_local
DATABASE_URL="postgresql://symfony:symfony@127.0.0.1:5432/aufgaben_manager?serverVersion=16&charset=utf8"

Configuration files in config/

Every installed bundle brings its own configuration file under config/packages/ – e.g. config/packages/doctrine.yaml for Doctrine (block 4) or config/packages/security.yaml for security (block 5). These YAML files frequently use environment variables as placeholders:

doctrine:
    dbal:
        url: '%env(resolve:DATABASE_URL)%'
    orm:
        auto_generate_proxy_classes: true
        enable_lazy_ghost_objects: true

%env(resolve:DATABASE_URL)% reads the DATABASE_URL environment variable's value from the .env* files – the actual configuration file stays identical across ALL environments this way, only the environment variable differs.

Environment-specific configuration overrides

Inside config/packages/, per-environment subfolders can be created, whose contents are loaded ONLY in that environment:

config/packages/
├── doctrine.yaml       (loaded in ALL environments)
├── dev/
│   └── monolog.yaml    (loaded ONLY in dev: verbose logging)
└── prod/
    └── monolog.yaml    (loaded ONLY in prod: reduced logging)

Understanding the configuration cache

In prod, Symfony compiles ALL configuration (routes, services, container) ONCE into highly optimized PHP code under var/cache/prod/ – later changes to config/ do NOT take effect automatically there until the cache is explicitly cleared:

php bin/console cache:clear --env=prod