How to Master and Create new Environments

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Every application is the combination of code and a set of configuration that dictates how that code should function. The configuration may define the database being used, if something should be cached or how verbose logging should be.

In Symfony, the idea of "environments" is the idea that the same codebase can be run using multiple different configurations. For example, the dev environment should use configuration that makes development easy and friendly, while the prod environment should use a set of configuration optimized for speed.

Different Environments, different Configuration Files

A typical Symfony application begins with three environments: dev, prod, and test. As mentioned, 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)
    {
        $loader->load($this->getProjectDir().'/app/config/config_'.$this->getEnvironment().'.yml');
    }
}

As you can see, when Symfony 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.

However, in practice each environment differs only somewhat from others. Generally, all environments will share a large base of common configuration. Opening the config_dev.yml configuration file, you can see how this is accomplished:

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imports:
    - { resource: config.yml }

# ...

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 value of the toolbar option in the config_dev.yml configuration file:

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

web_profiler:
    toolbar: true
    # ...

Executing an Application in different Environments

To execute the application in each environment, load up the application using either app.php (for the prod environment) or 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 don't have either filename in your URL, then it's up to your web server to decide which file to execute behind the scenes. If you're using the built-in PHP web server, it knows to use the app_dev.php file. On production, you'll configure your web server to use app.php. Either way: one of these two files is always executed.

Note

The given URLs assume that your web server is configured to use the web/ directory of the application as its root. Read more in Installing Symfony.

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);

// ...

The prod key specifies that this application will run in the prod environment. A Symfony application can be executed in any environment by using this code and changing the environment string.

Note

The test environment is used when writing functional tests and is not accessible in the browser directly via a front controller. In other words, unlike the other environments, there is no app_test.php front controller file.

Debug Mode

Important, but unrelated to the topic of environments is the false argument as the second argument to the AppKernel constructor. This specifies if the application should run in "debug mode". Regardless of the environment, a Symfony application can be run with debug mode set to true or false. This affects many things in the application, such as displaying stacktraces on error pages or if cache files are dynamically rebuilt on each request. Though not a requirement, debug mode is generally set to true for the dev and test environments and false for the prod environment.

Internally, the value of the debug mode becomes the kernel.debug parameter used inside the service container. If you look inside the application configuration file, you'll see the parameter used, for example, to turn logging on or off when using the Doctrine DBAL:

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

Selecting the Environment for Console Commands

By default, Symfony commands are executed in the dev environment and with the debug mode enabled. Use the --env and --no-debug options to modify this behavior:

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# 'dev' environment and debug enabled
$ php bin/console command_name

# 'prod' environment (debug is always disabled for 'prod')
$ php bin/console command_name --env=prod

# 'test' environment and debug disabled
$ php bin/console command_name --env=test --no-debug

In addition to the --env and --no-debug options, the behavior of Symfony commands can also be controlled with environment variables. The Symfony console application checks the existence and value of these environment variables before executing any command:

SYMFONY_ENV
Sets the execution environment of the command to the value of this variable (dev, prod, test, etc.);
SYMFONY_DEBUG
If 0, debug mode is disabled. Otherwise, debug mode is enabled.

These environment variables are very useful for production servers because they allow you to ensure that commands always run in the prod environment without having to add any command option.

Creating a new Environment

By default, a Symfony application has three environments that handle most cases. However, 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 Symfony's web_profiler enabled. This allows Symfony 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 }

Note

Due to the way in which parameters are resolved, you cannot use them to build paths in imports dynamically. This means that something like the following doesn't work:

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# app/config/config.yml
imports:
    - { resource: '%kernel.project_dir%/app/parameters.yml' }

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

Note

Some environments, like the dev environment, are never meant to be accessed on any deployed server by the public. This is because certain environments, for debugging purposes, may give too much information about the application or underlying infrastructure. To be sure these environments aren't accessible, the front controller is usually protected from external IP addresses via the following code at the top of the controller:

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if (!in_array(@$_SERVER['REMOTE_ADDR'], ['127.0.0.1', '::1'])) {
    die('You are not allowed to access this file. Check '.basename(__FILE__).' for more information.');
}

Environments and the Cache Directory

Symfony 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 var/cache directory. However, each environment caches its own set of files:

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your-project/
├─ var/
│  ├─ cache/
│  │  ├─ dev/   # cache directory for the *dev* environment
│  │  └─ 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 var/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.

Note

You can change the directory location and name. For more information read the article How to Override Symfony's default Directory Structure.

Going further

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

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