Best Practices for Reusable Bundles

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Best Practices for Reusable Bundles

This article is all about how to structure your reusable bundles to be configurable and extendable. Reusable bundles are those meant to be shared privately across many company projects or publicly so any Symfony project can install them.

Bundle Name

A bundle is also a PHP namespace. The namespace must follow the PSR-4 interoperability standard for PHP namespaces and class names: it starts with a vendor segment, followed by zero or more category segments, and it ends with the namespace short name, which must end with Bundle.

A namespace becomes a bundle as soon as you add a bundle class to it. The bundle class name must follow these rules:

  • Use only alphanumeric characters and underscores;
  • Use a StudlyCaps name (i.e. camelCase with an uppercase first letter);
  • Use a descriptive and short name (no more than two words);
  • Prefix the name with the concatenation of the vendor (and optionally the category namespaces);
  • Suffix the name with Bundle.

Here are some valid bundle namespaces and class names:

Namespace Bundle Class Name
Acme\Bundle\BlogBundle AcmeBlogBundle
Acme\BlogBundle AcmeBlogBundle

By convention, the getName() method of the bundle class should return the class name.


If you share your bundle publicly, you must use the bundle class name as the name of the repository (AcmeBlogBundle and not BlogBundle for instance).


Symfony core Bundles do not prefix the Bundle class with Symfony and always add a Bundle sub-namespace; for example: FrameworkBundle.

Each bundle has an alias, which is the lower-cased short version of the bundle name using underscores (acme_blog for AcmeBlogBundle). This alias is used to enforce uniqueness within a project and for defining bundle's configuration options (see below for some usage examples).

Directory Structure

The basic directory structure of an AcmeBlogBundle must read as follows:

├─ AcmeBlogBundle.php
├─ Controller/
├─ Resources/
│   ├─ config/
│   ├─ doc/
│   │  └─ index.rst
│   ├─ translations/
│   ├─ views/
│   └─ public/
└─ Tests/

The following files are mandatory, because they ensure a structure convention that automated tools can rely on:

  • AcmeBlogBundle.php: This is the class that transforms a plain directory into a Symfony bundle (change this to your bundle's name);
  • This file contains the basic description of the bundle and it usually shows some basic examples and links to its full documentation (it can use any of the markup formats supported by GitHub, such as README.rst);
  • LICENSE: The full contents of the license used by the code. Most third-party bundles are published under the MIT license, but you can choose any license;
  • Resources/doc/index.rst: The root file for the Bundle documentation.

The depth of subdirectories should be kept to a minimum for the most used classes and files. Two levels is the maximum.

The bundle directory is read-only. If you need to write temporary files, store them under the cache/ or log/ directory of the host application. Tools can generate files in the bundle directory structure, but only if the generated files are going to be part of the repository.

The following classes and files have specific emplacements (some are mandatory and others are just conventions followed by most developers):

Type Directory
Commands Command/
Controllers Controller/
Service Container Extensions DependencyInjection/
Doctrine ORM entities (when not using annotations) Entity/
Doctrine ODM documents (when not using annotations) Document/
Event Listeners EventListener/
Configuration (routes, services, etc.) Resources/config/
Web Assets (CSS, JS, images) Resources/public/
Translation files Resources/translations/
Validation (when not using annotations) Resources/config/validation/
Serialization (when not using annotations) Resources/config/serialization/
Templates Resources/views/
Unit and Functional Tests Tests/


The bundle directory structure is used as the namespace hierarchy. For instance, a ContentController controller which is stored in Acme/BlogBundle/Controller/ContentController.php would have the fully qualified class name of Acme\BlogBundle\Controller\ContentController.

All classes and files must follow the Symfony coding standards.

Some classes should be seen as facades and should be as short as possible, like Commands, Helpers, Listeners and Controllers.

Classes that connect to the event dispatcher should be suffixed with Listener.

Exception classes should be stored in an Exception sub-namespace.


A bundle must not embed third-party PHP libraries. It should rely on the standard Symfony autoloading instead.

A bundle should also not embed third-party libraries written in JavaScript, CSS or any other language.


A bundle should come with a test suite written with PHPUnit and stored under the Tests/ directory. Tests should follow the following principles:

  • The test suite must be executable with a simple phpunit command run from a sample application;
  • The functional tests should only be used to test the response output and some profiling information if you have some;
  • The tests should cover at least 95% of the code base.


A test suite must not contain AllTests.php scripts, but must rely on the existence of a phpunit.xml.dist file.

Continuous Integration

Testing bundle code continuously, including all its commits and pull requests, is a good practice called Continuous Integration. There are several services providing this feature for free for open source projects, like GitHub Actions and Travis CI.

A bundle should at least test:

  • The lower bound of their dependencies (by running composer update --prefer-lowest);
  • The supported PHP versions;
  • All supported major Symfony versions (e.g. both 4.x and 5.x if support is claimed for both).

Thus, a bundle supporting PHP 7.3, 7.4 and 8.0, and Symfony 4.4 and 5.x should have at least this test matrix:

PHP version Symfony version Composer flags
7.3 4.* --prefer-lowest
7.4 5.*  
8.0 5.*  


The tests should be run with the SYMFONY_DEPRECATIONS_HELPER env variable set to max[direct]=0. This ensures no code in the bundle uses deprecated features directly.

The lowest dependency tests can be run with this variable set to disabled=1.

Require a Specific Symfony Version

You can use the special SYMFONY_REQUIRE environment variable together with Symfony Flex to install a specific Symfony version:

# this requires Symfony 5.x for all Symfony packages

# install Symfony Flex in the CI environment
composer global require --no-progress --no-scripts --no-plugins symfony/flex

# install the dependencies (using --prefer-dist and --no-progress is
# recommended to have a better output and faster download time)
composer update --prefer-dist --no-progress


If you want to cache your Composer dependencies, do not cache the vendor/ directory as this has side-effects. Instead cache $HOME/.composer/cache/files.


Bundles should set "type": "symfony-bundle" in their composer.json file. With this, Symfony Flex will be able to automatically enable your bundle when it's installed.

If your bundle requires any setup (e.g. configuration, new files, changes to .gitignore, etc), then you should create a Symfony Flex recipe.


All classes and functions must come with full PHPDoc.

Extensive documentation should also be provided in the Resources/doc/ directory. The index file (for example Resources/doc/index.rst or Resources/doc/ is the only mandatory file and must be the entry point for the documentation. The reStructuredText (rST) is the format used to render the documentation on the Symfony website.

Installation Instructions

In order to ease the installation of third-party bundles, consider using the following standardized instructions in your file.

  • Markdown
  • RST

Make sure Composer is installed globally, as explained in the
[installation chapter](
of the Composer documentation.

Applications that use Symfony Flex

Open a command console, enter your project directory and execute:

$ composer require <package-name>

Applications that don't use Symfony Flex

### Step 1: Download the Bundle

Open a command console, enter your project directory and execute the
following command to download the latest stable version of this bundle:

$ composer require <package-name>

### Step 2: Enable the Bundle

Then, enable the bundle by adding it to the list of registered bundles
in the `config/bundles.php` file of your project:

// config/bundles.php

return [
    // ...
    <vendor>\<bundle-name>\<bundle-long-name>::class => ['all' => true],

The example above assumes that you are installing the latest stable version of the bundle, where you don't have to provide the package version number (e.g. composer require friendsofsymfony/user-bundle). If the installation instructions refer to some past bundle version or to some unstable version, include the version constraint (e.g. composer require friendsofsymfony/user-bundle "~2.0@dev").

Optionally, you can add more installation steps (Step 3, Step 4, etc.) to explain other required installation tasks, such as registering routes or dumping assets.


If the bundle provides routes, they must be prefixed with the bundle alias. For example, if your bundle is called AcmeBlogBundle, all its routes must be prefixed with acme_blog_.


If a bundle provides templates, they must use Twig. A bundle must not provide a main layout, except if it provides a full working application.

Translation Files

If a bundle provides message translations, they must be defined in the XLIFF format; the domain should be named after the bundle name (acme_blog).

A bundle must not override existing messages from another bundle.


To provide more flexibility, a bundle can provide configurable settings by using the Symfony built-in mechanisms.

For simple configuration settings, rely on the default parameters entry of the Symfony configuration. Symfony parameters are simple key/value pairs; a value being any valid PHP value. Each parameter name should start with the bundle alias, though this is just a best-practice suggestion. The rest of the parameter name will use a period (.) to separate different parts (e.g.

The end user can provide values in any configuration file:

  • YAML
  • XML
  • PHP
# config/services.yaml
parameters: ''

Retrieve the configuration parameters in your code from the container:


While this mechanism requires the least effort, you should consider using the more advanced semantic bundle configuration to make your configuration more robust.


Bundles must be versioned following the Semantic Versioning Standard.


If the bundle defines services, they must be prefixed with the bundle alias instead of using fully qualified class names like you do in your project services. For example, AcmeBlogBundle services must be prefixed with acme_blog. The reason is that bundles shouldn't rely on features such as service autowiring or autoconfiguration to not impose an overhead when compiling application services.

In addition, services not meant to be used by the application directly, should be defined as private. For public services, aliases should be created from the interface/class to the service id. For example, in MonologBundle, an alias is created from Psr\Log\LoggerInterface to logger so that the LoggerInterface type-hint can be used for autowiring.

Services should not use autowiring or autoconfiguration. Instead, all services should be defined explicitly.

See also

You can learn much more about service loading in bundles reading this article: How to Load Service Configuration inside a Bundle.

Composer Metadata

The composer.json file should include at least the following metadata:

Consists of the vendor and the short bundle name. If you are releasing the bundle on your own instead of on behalf of a company, use your personal name (e.g. johnsmith/blog-bundle). Exclude the vendor name from the bundle short name and separate each word with an hyphen. For example: AcmeBlogBundle is transformed into blog-bundle and AcmeSocialConnectBundle is transformed into social-connect-bundle.
A brief explanation of the purpose of the bundle.
Use the symfony-bundle value.
a string (or array of strings) with a valid license identifier, such as MIT.
This information is used by Symfony to load the classes of the bundle. It's recommended to use the PSR-4 autoload standard: use the namespace as key, and the location of the bundle's main class (relative to composer.json) as value. For example, if the main class is located in the bundle root directory: "autoload": { "psr-4": { "SomeVendor\\BlogBundle\\": "" } }. If the main class is located in the src/ directory of the bundle: "autoload": { "psr-4": { "SomeVendor\\BlogBundle\\": "src/" } }.

In order to make it easier for developers to find your bundle, register it on Packagist, the official repository for Composer packages.


If the bundle references any resources (config files, translation files, etc.), don't use physical paths (e.g. __DIR__/config/services.xml) but logical paths (e.g. @FooBundle/Resources/config/services.xml).

The logical paths are required because of the bundle overriding mechanism that lets you override any resource/file of any bundle. See The HttpKernel Component for more details about transforming physical paths into logical paths.

Beware that templates use a simplified version of the logical path shown above. For example, an index.html.twig template located in the Resources/views/Default/ directory of the FooBundle, is referenced as @Foo/Default/index.html.twig.

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