Infrastructure-Related Configuration
- Canonical Parameters
Application-Related Configuration
- Constants vs Configuration Options
Parameter Naming

Configuration

Configuration usually involves different application parts (such as infrastructure and security credentials) and different environments (development, production). That's why Symfony recommends that you split the application configuration into three parts.

These are the options that change from one machine to another (e.g. from your development machine to the production server) but which don't change the application behavior.

Best Practice

Define the infrastructure-related configuration options as environment variables. During development, use the .env file at the root of your project to set these.

By default, Symfony adds these types of options to the .env file when installing new dependencies in the app:

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        # .env
###> doctrine/doctrine-bundle ###
DATABASE_URL=sqlite:///%kernel.project_dir%/var/data/blog.sqlite
###< doctrine/doctrine-bundle ###

###> symfony/swiftmailer-bundle ###
MAILER_URL=smtp://localhost?encryption=ssl&auth_mode=login&username=&password=
###< symfony/swiftmailer-bundle ###

# ...
    

These options aren't defined inside the config/services.yaml file because they have nothing to do with the application's behavior. In other words, your application doesn't care about the location of your database or the credentials to access to it, as long as the database is correctly configured.

Caution

Beware that dumping the contents of the $_SERVER and $_ENV variables or outputting the phpinfo() contents will display the values of the environment variables, exposing sensitive information such as the database credentials.

Canonical Parameters

Best Practice

Define all your application's env vars in the .env.dist file.

Symfony includes a configuration file called .env.dist at the project root, which stores the canonical list of environment variables for the application.

Whenever a new env var is defined for the application, you should also add it to this file and submit the changes to your version control system so your workmates can update their .env files.

Best Practice

Define the application behavior related configuration options in the config/services.yaml file.

The services.yaml file contains the options used by the application to modify its behavior, such as the sender of email notifications, or the enabled feature toggles. Defining these values in .env file would add an extra layer of configuration that's not needed because you don't need or want these configuration values to change on each server.

The configuration options defined in the services.yaml may vary from one environment to another. That's why Symfony supports defining config/services_dev.yaml and config/services_prod.yaml files so that you can override specific values for each environment.

Constants vs Configuration Options

One of the most common errors when defining application configuration is to create new options for values that never change, such as the number of items for paginated results.

Best Practice

Use constants to define configuration options that rarely change.

The traditional approach for defining configuration options has caused many Symfony apps to include an option like the following, which would be used to control the number of posts to display on the blog homepage:

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        # config/services.yaml
parameters:
    homepage.number_of_items: 10
    

If you've done something like this in the past, it's likely that you've in fact never actually needed to change that value. Creating a configuration option for a value that you are never going to configure just isn't necessary. Our recommendation is to define these values as constants in your application. You could, for example, define a NUMBER_OF_ITEMS constant in the Post entity:

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        // src/Entity/Post.php
namespace App\Entity;

class Post
{
    const NUMBER_OF_ITEMS = 10;

    // ...
}
    

The main advantage of defining constants is that you can use their values everywhere in your application. When using parameters, they are only available from places with access to the Symfony container.

Constants can be used for example in your Twig templates thanks to the constant() function:

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        <p>
    Displaying the {{ constant('NUMBER_OF_ITEMS', post) }} most recent results.
</p>
    

And Doctrine entities and repositories can now easily access these values, whereas they cannot access the container parameters:

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        namespace App\Repository;

use App\Entity\Post;
use Doctrine\ORM\EntityRepository;

class PostRepository extends EntityRepository
{
    public function findLatest($limit = Post::NUMBER_OF_ITEMS)
    {
        // ...
    }
}
    

The only notable disadvantage of using constants for this kind of configuration values is that you cannot redefine them easily in your tests.

Parameter Naming

Best Practice

The name of your configuration parameters should be as short as possible and should include a common prefix for the entire application.

Using app. as the prefix of your parameters is a common practice to avoid collisions with Symfony and third-party bundles/libraries parameters. Then, use just one or two words to describe the purpose of the parameter:

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        # config/services.yaml
parameters:
    # don't do this: 'dir' is too generic and it doesn't convey any meaning
    app.dir: '...'
    # do this: short but easy to understand names
    app.contents_dir: '...'
    # it's OK to use dots, underscores, dashes or nothing, but always
    # be consistent and use the same format for all the parameters
    app.dir.contents: '...'
    app.contents-dir: '...'
    

Next: Organizing Your Business Logic

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.