Different Environments, Different Configuration Files

A typical Symfony2 application begins with three environments: dev, prod, and test. As discussed, each "environment" simply represents a way to execute the same codebase with different configuration. It should be no surprise then that each environment loads its own individual configuration file. If you're using the YAML configuration format, the following files are used:

• for the dev environment: app/config/config_dev.yml
• for the prod environment: app/config/config_prod.yml
• for the test environment: app/config/config_test.yml

This works via a simple standard that's used by default inside the AppKernel class:

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// app/AppKernel.php

// ...

class AppKernel extends Kernel
{
    // ...

    public function registerContainerConfiguration(LoaderInterface $loader)
    {
        $loader->load(__DIR__.'/config/config_'.$this->getEnvironment().'.yml');
    }
}

As you can see, when Symfony2 is loaded, it uses the given environment to determine which configuration file to load. This accomplishes the goal of multiple environments in an elegant, powerful and transparent way.

Of course, in reality, each environment differs only somewhat from others. Generally, all environments will share a large base of common configuration. Opening the "dev" configuration file, you can see how this is accomplished easily and transparently:

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imports:
    - { resource: config.yml }
# ...

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<imports>
    <import resource="config.xml" />
</imports>
<!-- ... -->

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$loader->import('config.php');
// ...

To share common configuration, each environment's configuration file simply first imports from a central configuration file (config.yml). The remainder of the file can then deviate from the default configuration by overriding individual parameters. For example, by default, the web_profiler toolbar is disabled. However, in the dev environment, the toolbar is activated by modifying the default value in the dev configuration file:

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# app/config/config_dev.yml
imports:
    - { resource: config.yml }

web_profiler:
    toolbar: true
    # ...

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<!-- app/config/config_dev.xml -->
<imports>
    <import resource="config.xml" />
</imports>

<webprofiler:config
    toolbar="true"
    ... />

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// app/config/config_dev.php
$loader->import('config.php');

$container->loadFromExtension('web_profiler', array(
    'toolbar' => true,

    // ...
));

Executing an Application in Different Environments

To execute the application in each environment, load up the application using either the app.php (for the prod environment) or the app_dev.php (for the dev environment) front controller:

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http://localhost/app.php      -> *prod* environment
http://localhost/app_dev.php  -> *dev* environment

If you open up one of these files, you'll quickly see that the environment used by each is explicitly set:

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// web/app.php
// ... 

$kernel = new AppKernel('prod', false);

// ...

As you can see, the prod key specifies that this environment will run in the prod environment. A Symfony2 application can be executed in any environment by using this code and changing the environment string.

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doctrine:
   dbal:
       logging:  "%kernel.debug%"
       # ...

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<doctrine:dbal logging="%kernel.debug%" ... />

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$container->loadFromExtension('doctrine', array(
    'dbal' => array(
        'logging'  => '%kernel.debug%',

        // ...
    ),
    // ...
));

Creating a New Environment

By default, a Symfony2 application has three environments that handle most cases. Of course, since an environment is nothing more than a string that corresponds to a set of configuration, creating a new environment is quite easy.

Suppose, for example, that before deployment, you need to benchmark your application. One way to benchmark the application is to use near-production settings, but with Symfony2's web_profiler enabled. This allows Symfony2 to record information about your application while benchmarking.

The best way to accomplish this is via a new environment called, for example, benchmark. Start by creating a new configuration file:

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# app/config/config_benchmark.yml
imports:
    - { resource: config_prod.yml }

framework:
    profiler: { only_exceptions: false }

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<!-- app/config/config_benchmark.xml -->
<imports>
    <import resource="config_prod.xml" />
</imports>

<framework:config>
    <framework:profiler only-exceptions="false" />
</framework:config>

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// app/config/config_benchmark.php
$loader->import('config_prod.php')

$container->loadFromExtension('framework', array(
    'profiler' => array('only-exceptions' => false),
));

And with this simple addition, the application now supports a new environment called benchmark.

This new configuration file imports the configuration from the prod environment and modifies it. This guarantees that the new environment is identical to the prod environment, except for any changes explicitly made here.

Because you'll want this environment to be accessible via a browser, you should also create a front controller for it. Copy the web/app.php file to web/app_benchmark.php and edit the environment to be benchmark:

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// web/app_benchmark.php


// change just this line
$kernel = new AppKernel('benchmark', false);

// ...

The new environment is now accessible via:

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http://localhost/app_benchmark.php

Environments and the Cache Directory

Symfony2 takes advantage of caching in many ways: the application configuration, routing configuration, Twig templates and more are cached to PHP objects stored in files on the filesystem.

By default, these cached files are largely stored in the app/cache directory. However, each environment caches its own set of files:

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app/cache/dev   - cache directory for the *dev* environment
app/cache/prod  - cache directory for the *prod* environment

Sometimes, when debugging, it may be helpful to inspect a cached file to understand how something is working. When doing so, remember to look in the directory of the environment you're using (most commonly dev while developing and debugging). While it can vary, the app/cache/dev directory includes the following:

• appDevDebugProjectContainer.php - the cached "service container" that represents the cached application configuration;
• appDevUrlGenerator.php - the PHP class generated from the routing configuration and used when generating URLs;
• appDevUrlMatcher.php - the PHP class used for route matching - look here to see the compiled regular expression logic used to match incoming URLs to different routes;
• twig/ - this directory contains all the cached Twig templates.

Going Further

Read the article on How to Set External Parameters in the Service Container.