Symfony 4: Compose your Applications

Fabien Potencier
5 min readApr 3, 2017

Note: Symfony 4.0 will be released at the end of November 2017. During the next few weeks, I will publish articles about my ideas and the main changes I want to implement for Symfony 4.

Symfony 3.0 was boring, a cleaned-up version of the Symfony 2.8 version:

Symfony 3.0 = Symfony 2.8 — deprecated features

Symfony 4.0 will be different:

Symfony 4.0 = Symfony 3.4 — deprecated features + a new way to develop applications

There is another way to think about a new major version though:

Symfony 4.0 = Symfony 3.0 + all features added in 3.x — deprecated features + a new way to develop applications

Symfony 4.0 will also require PHP 7.

While thinking about what needs to be changed for Symfony 4, I thought about the day-to-day experience of managing an application.

Installing a Bundle is too cumbersome

The current best way to add more dependencies to a Symfony application is to install bundles and libraries via Composer packages.

Fun fact: Composer started as a conversation about how to generically install bundles/plugins/extensions for Symfony and phpBB.

WTF fact: Neither Symfony nor phpBB uses Composer as a way to install its bundles/plugins/extensions.

When installing a Symfony bundle, using Composer is not enough; you also need to enable and configure the bundle correctly before using its features. Here are the typical steps you need to perform:

  • Execute composer require symfony/bundle; it must be manual as developers are in charge of selecting the packages they want to install; however, we will see that we can make it better when installing dependencies in the context of a Symfony application (hint: wouldn't it be cool to run composer req cli, composer req admin, or composer req mailer?);
  • Register the bundle in the AppKernel class;
  • Register some routes (optional);
  • Configure the bundle as you see fit.

The first step cannot be automated, but it feels like the other ones could be. Configuration cannot be automated but we can probably generate good defaults like done in the Symfony Standard Edition for some bundles.

Have a look at the documentation of popular bundles. Their READMEs all start with the same boring dance.

Removing a Bundle is even more cumbersome

From time to time you might want to remove a bundle. How can you do that? Simple enough: composer remove symfony/bundle.

Well, that’s not enough.

Remember how we needed to register the bundle, add routes wiring, and configuration? We need to undo that now, too. This means visiting several files to remove the bundle. This makes removing a bundle a boring and error-prone process.

The Symfony Standard Edition is not good enough

Symfony Distributions was an attempt to fix some of these issues by providing a good starting point.

The most popular one, the Symfony Standard Edition, is “optimized” for “traditional” frontend applications for which you need a database, a templating system, and a way to send emails. But is it still relevant? What if you want to start a micro-framework style application? Or an API/web service one?

The Symfony Standard Edition makes choices for the developer, but either too few or too many. Symfony Distributions do not scale well; it is not easy to remove dependencies, and it is not that easy to add new ones.

Another issue with distributions is that they come with files that you don’t want for your project. Like the LICENSE and the README files. Most projects are not MIT-licensed and the authors are probably different from the ones who worked on the distribution. In the same vein, you have to change almost all entries of the composer.json file.

Removing a few files is no problem, but it adds up quickly.

A few years back, the Symfony Standard Edition came with a small demo to get you started faster. But we removed it as people had a hard time cleaning things up as the demo spanned many files. It was both a good and a bad decision. It made the Standard Edition worse as developers don’t have any examples anymore, but it made it also better as developers don’t need to clean things up manually anymore.

Not convinced yet? Have a look at the REST distribution README file:

No Distribution Ecosystem

And that’s probably why Symfony Distributions never took off. Apart from the Standard Edition, not a single one is popular; and as a matter of fact, we only list three of them on

Distributions are not flexible enough. You cannot switch from one to another. You need to buy all their choices or nothing. They cannot evolve.

Distributions is the wrong abstraction. We don’t need a fully bootstrapped project. We need a way to grow an application over time.

The ideal Experience

As a developer, I want to start small, without too many dependencies. But I also want to be able to grow my application as I see fit. From a micro-framework style app to a gigantic monolith. Your choice. The framework should not get in the way.

Starting a new project with Symfony or evolving a project is currently too complex for beginners and too cumbersome for advanced Symfony developers. We can do better.

Composition over Inheritance

If you think about it, distributions use inheritance. Most distributions are forks of the Symfony Standard Edition with additional bundles. What about using composition instead? I want to use the API distribution with the admin generator one. Or do we even need distributions? Probably not.

Enter Symfony Flex, a new way to create and evolve your applications with ease.

Symfony Flex is all about making it simple and easy to create any Symfony applications, from the most simple micro-style project to the more complex ones with dozens of dependencies. It automates adding and removing bundles. It takes care of giving you sensible defaults. It helps discovering good bundles.

Symfony Flex is going to be the default way to manage Symfony 4 applications. But Symfony Flex will be available as an option to manage Symfony 3.3 and 3.4 applications as well! That said, we might need to break backward compatibility between now and the launch of Symfony 4. Consider Symfony Flex as alpha before Symfony 4.

Stay tuned as the next post will tell you more about Symfony Flex. In the meantime, have a look at the new skeleton application used by Symfony Flex. Not what you would have expected, right?

Originally published at



Fabien Potencier

founder and CEO @SensioLabs and @blackfireio, founder and project lead @Symfony