Environment Variable Processors

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Environment Variable Processors

Using env vars to configure Symfony applications is a common practice to hide sensitive configuration (e.g. database credentials) and to make your applications truly dynamic.

The main issue of env vars is that their values can only be strings and your application may need other data types (integer, boolean, etc.). Symfony solves this problem with "env var processors", which transform the original 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)%'
    

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        <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <framework:config>
        <framework:router http-port="%env(int:HTTP_PORT)%"/>
    </framework:config>
</container>
    

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        // config/packages/framework.php
$container->loadFromExtension('framework', [
    'router' => [
        'http_port' => '%env(int:HTTP_PORT)%',
    ],
]);
    

Built-In Environment Variable Processors

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)%'
    

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        <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(SECRET)">some_secret</parameter>
    </parameters>

    <framework:config secret="%env(string:SECRET)%"/>
</container>
    

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        // config/packages/framework.php
$container->setParameter('env(SECRET)', 'some_secret');
$container->loadFromExtension('framework', [
    'secret' => '%env(string:SECRET)%',
]);
    

env(bool:FOO)

Casts FOO to a bool:

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        # config/packages/framework.yaml
parameters:
    env(HTTP_METHOD_OVERRIDE): 'true'
framework:
    http_method_override: '%env(bool:HTTP_METHOD_OVERRIDE)%'
    

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        <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(HTTP_METHOD_OVERRIDE)">true</parameter>
    </parameters>

    <framework:config http-methode-override="%env(bool:HTTP_METHOD_OVERRIDE)%"/>
</container>
    

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        // config/packages/framework.php
$container->setParameter('env(HTTP_METHOD_OVERRIDE)', 'true');
$container->loadFromExtension('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)%' }
    

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        <!-- config/packages/security.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:security="http://symfony.com/schema/dic/security"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <parameters>
        <parameter key="env(HEALTH_CHECK_METHOD)">Symfony\Component\HttpFoundation\Request::METHOD_HEAD</parameter>
    </parameters>

    <security:config>
        <rule path="^/health-check$" methods="%env(const:HEALTH_CHECK_METHOD)%"/>
    </security:config>
</container>
    

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        // config/packages/security.php
$container->setParameter('env(HEALTH_CHECK_METHOD)', 'Symfony\Component\HttpFoundation\Request::METHOD_HEAD');
$container->loadFromExtension('security', [
    'access_control' => [
        [
            'path' => '^/health-check$',
            '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:

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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)%'
    

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        <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(TRUSTED_HOSTS)">["10.0.0.1", "10.0.0.2"]</parameter>
    </parameters>

    <framework:config trusted-hosts="%env(json:TRUSTED_HOSTS)%"/>
</container>
    

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        // config/packages/framework.php
$container->setParameter('env(TRUSTED_HOSTS)', '["10.0.0.1", "10.0.0.2"]');
$container->loadFromExtension('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'
    sentry_host: '%env(HOST)%'
    env(SENTRY_DSN): 'http://%sentry_host%/project'
sentry:
    dsn: '%env(resolve:SENTRY_DSN)%'
    

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        <!-- config/packages/sentry.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <parameters>
        <parameter key="env(HOST)">10.0.0.1</parameter>
        <parameter key="sentry_host">%env(HOST)%</parameter>
        <parameter key="env(SENTRY_DSN)">http://%sentry_host%/project</parameter>
    </parameters>

    <sentry:config dsn="%env(resolve:SENTRY_DSN)%"/>
</container>
    

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        // config/packages/sentry.php
$container->setParameter('env(HOST)', '10.0.0.1');
$container->setParameter('sentry_host', '%env(HOST)%');
$container->setParameter('env(SENTRY_DSN)', 'http://%sentry_host%/project');
$container->loadFromExtension('sentry', [
    'dsn' => '%env(resolve:SENTRY_DSN)%',
]);
    

env(csv:FOO)

Decodes the content of FOO, which is a CSV-encoded string:

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        parameters:
    env(TRUSTED_HOSTS): "10.0.0.1, 10.0.0.2"
framework:
   trusted_hosts: '%env(csv:TRUSTED_HOSTS)%'
    

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)%'
    

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        <!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(AUTH_FILE)">../config/auth.json</parameter>
    </parameters>

    <google auth="%env(file:AUTH_FILE)%"/>
</container>
    

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        // config/packages/framework.php
$container->setParameter('env(AUTH_FILE)', '../config/auth.json');
$container->loadFromExtension('google', [
    'auth' => '%env(file:AUTH_FILE)%',
]);
    

env(key:FOO:BAR)

Retrieves the value associated with the key FOO from the array whose contents are stored in the BAR env var:

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        # config/services.yaml
parameters:
    env(SECRETS_FILE): '/opt/application/.secrets.json'
    database_password: '%env(key:database_password:json:file:SECRETS_FILE)%'
    # if SECRETS_FILE contents are: {"database_password": "secret"} it returns "secret"
    

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        <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <parameters>
        <parameter key="env(SECRETS_FILE)">/opt/application/.secrets.json</parameter>
        <parameter key="database_password">%env(key:database_password:json:file:SECRETS_FILE)%</parameter>
    </parameters>
</container>
    

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        // config/services.php
$container->setParameter('env(SECRETS_FILE)', '/opt/application/.secrets.json');
$container->setParameter('database_password', '%env(key:database_password:json:file:SECRETS_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:

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        use Symfony\Component\DependencyInjection\EnvVarProcessorInterface;

class LowercasingEnvVarProcessor implements EnvVarProcessorInterface
{
    public function getEnv($prefix, $name, \Closure $getEnv)
    {
        $env = $getEnv($name);

        return strtolower($env);
    }

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

To enable the new processor in the app, register it as a service and tag it with the container.env_var_processor tag. If you're using the default services.yaml configuration, this is already done for you, thanks to autoconfiguration.

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

Environment Variable Processors

Environment Variable Processors

Built-In Environment Variable Processors

Custom Environment Variable Processors

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