How to Set external Parameters in the Service Container

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How to Set external Parameters in the Service Container

In Configuring Symfony (and Environments), you learned how to manage your application configuration. At times, it may benefit your application to store certain credentials outside of your project code. Database configuration is one such example. The flexibility of the Symfony service container allows you to easily do this.

Environment Variables

You can reference environment variables by using special parameters named after the variables you want to use enclosed between env(). Their actual values will be resolved at runtime (once per request), so that dumped containers can be reconfigured dynamically even after being compiled.

For example, when installing the doctrine recipe, database configuration is put in a DATABASE_URL environment variable:

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# .env
DATABASE_URL="mysql://db_user:db_password@127.0.0.1:3306/db_name"

This variable is referenced in the service container configuration using %env(DATABASE_URL)%:

  • YAML
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  • PHP 
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# config/packages/doctrine.yaml
doctrine:
    dbal:
        url: '%env(DATABASE_URL)%'
    # ...

You can also give the env() parameters a default value: the default value will be used whenever the corresponding environment variable is not found:

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# config/services.yaml
parameters:
    env(DATABASE_HOST): localhost

Configuring Environment Variables in Production

During development, you'll use the .env file to configure your environment variables. On your production server, it is recommended to configure these at the web server level. If you're using Apache or Nginx, you can use e.g. one of the following:

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  • Nginx 
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<VirtualHost *:80>
    # ...

    SetEnv DATABASE_URL "mysql://db_user:db_password@127.0.0.1:3306/db_name"
</VirtualHost>

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.

The values of the env vars are also exposed in the web interface of the Symfony profiler. In practice this shouldn't be a problem because the web profiler must never be enabled in production.

Environment Variable Processors

3.4

Environment variable processors were introduced in Symfony 3.4.

The values of environment variables are considered strings by default. However, your code may expect other data types, like integers or booleans. Symfony solves this problem with processors, which modify the contents of the given environment variables. The following example uses the integer processor to turn the value of the HTTP_PORT env var into an integer:

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# config/packages/framework.yaml
framework:
    router:
        http_port: env(int:HTTP_PORT)

Symfony provides the following env var processors:

env(string:FOO)

Casts FOO to a string:

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# config/packages/framework.yaml
parameters:
    env(SECRET): 'some_secret'
framework:
   secret: '%env(string:SECRET)%'
env(bool:FOO)

Casts FOO to a bool:

  • YAML
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# config/packages/framework.yaml
parameters:
    env(HTTP_METHOD_OVERRIDE): 'true'
framework:
   http_method_override: '%env(bool:HTTP_METHOD_OVERRIDE)%'
env(int:FOO)
Casts FOO to an int.
env(float:FOO)
Casts FOO to a float.
env(const:FOO)

Finds the const value named in FOO:

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# config/packages/security.yaml
parameters:
    env(HEALTH_CHECK_METHOD): 'Symfony\Component\HttpFoundation\Request::METHOD_HEAD'
security:
   access_control:
     - { path: '^/health-check$', methods: '%env(const:HEALTH_CHECK_METHOD)%' }
env(base64:FOO)
Decodes the content of FOO, which is a base64 encoded string.
env(json:FOO)

Decodes the content of FOO, which is a JSON encoded string. It returns either an array or null:

  • YAML
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# config/packages/framework.yaml
parameters:
    env(TRUSTED_HOSTS): '["10.0.0.1", "10.0.0.2"]'
framework:
   trusted_hosts: '%env(json:TRUSTED_HOSTS)%'
env(resolve:FOO)

Replaces the string FOO by the value of a config parameter with the same name:

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# config/packages/sentry.yaml
parameters:
    env(HOST): '10.0.0.1'
    env(SENTRY_DSN): 'http://%env(HOST)%/project'
sentry:
    dsn: '%env(resolve:SENTRY_DSN)%'
env(file:FOO)

Returns the contents of a file whose path is the value of the FOO env var:

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# config/packages/framework.yaml
parameters:
    env(AUTH_FILE): '../config/auth.json'
google:
    auth: '%env(file:AUTH_FILE)%'

It is also possible to combine any number of processors:

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parameters:
    env(AUTH_FILE): "%kernel.project_dir%/config/auth.json"
google:
    # 1. gets the value of the AUTH_FILE env var
    # 2. replaces the values of any config param to get the config path
    # 3. gets the content of the file stored in that path
    # 4. JSON-decodes the content of the file and returns it
    auth: '%env(json:file:resolve:AUTH_FILE)%'

Custom Environment Variable Processors

It's also possible to add your own processors for environment variables. First, create a class that implements EnvVarProcessorInterface and then, define a service for that class:

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class LowercasingEnvVarProcessor implements EnvVarProcessorInterface
{
    private $container;

    public function __construct(ContainerInterface $container)
    {
        $this->container = $container;
    }

    public function getEnv($prefix, $name, \Closure $getEnv)
    {
        $env = $getEnv($name);

        return strtolower($env);
    }

    public static function getProvidedTypes()
    {
        return [
            'lowercase' => 'string',
        ];
    }
}

Constants

The container also has support for setting PHP constants as parameters. See Introduction to Parameters for more details.

Miscellaneous Configuration

You can mix whatever configuration format you like (YAML, XML and PHP) in config/packages/. Importing a PHP file gives you the flexibility to add whatever is needed in the container. For instance, you can create a drupal.php file in which you set a database URL based on Drupal's database configuration:

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// config/packages/drupal.php

// import Drupal's configuration
include_once('/path/to/drupal/sites/default/settings.php');

// set a app.database_url parameter
$container->setParameter('app.database_url', $db_url);
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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