Symfony 4: Monolith vs Micro

Fabien Potencier
4 min readApr 5, 2017

This is the second installment in a series of articles about Symfony 4. The first one was about the current limitations of the Symfony Distribution model.

Monolith projects versus micro-applications; a never-ending debate. Both ways to develop applications are fine in my book. Symfony supports both. Even if the Symfony Standard Edition is probably more suitable for monolith projects as it depends on the symfony/symfony package. This meta-package contains all the Symfony components and some "core" bundles. Among other features, you get Twig and the Web Profiler. But technically, you don't need them if you are developing an API for your next mobile application.

Of course, some extra files under vendor/ don't change anything, but some developers think that their applications are more "bloated" because of those extra bits on their disk. It feels like those extra unused features make your application fat. This is mostly about perception though.

Silex took another approach where each individual components are required when needed. Does it make Silex simpler, more lightweight, or faster than Symfony? No. Nevertheless, Symfony 4 is going to be more similar to Silex in this regard.

Symfony Applications go minimal

Out is the dependency on symfony/symfony. A Symfony application will now depend on the individual Symfony components and bundles. This is probably the most significant change in the way you will develop applications with Symfony 4. The main reason is not because it helps reducing the number of files under vendor/ though. It opens up many great opportunities.

It helps with auto-configuration, one major Symfony 4 feature. When installing a bundle, Symfony will now configure it automatically with good defaults. Configuration also adapts according to your other dependencies.

Take the Symfony Framework Bundle as an example. Some features can be enabled or disabled, like form, validation, templating, serializer, assets, …

As of Symfony 3.2, form support is enabled by default, but you can disable it if you are not using it in your application. Why is it enabled by default? Because there is no way for Symfony to know if you will use forms in your application. Disabling it by default would lead to a slightly worse developer experience as that’s one configuration knob to tweak before your first form works.

Now, imagine an application where symfony/symfony is not a dependency. An application can start with just symfony/framework-bundle. Automatically enabling form support is now trivial: enable it when symfony/form is installed, disable it otherwise. Simple, no magic, no configuration, great developer experience. You will love Symfony 4.

As a great side-effect, performance is better as optional features are automatically disabled. Without any tweaks in configuration files. I will share some simple benchmarks in another post.

Going minimal also means that Symfony does not try to make assumptions anymore about your stack. Besides the removal of the LICENSE or README files in the skeleton, there is no Apache .htaccess files anymore. What if you are using Apache then? Well, you will have to wait for another post to get the answer, but I got you covered.


Removing the dependency on symfony/symfony helps with another Symfony 4 feature: auto-discovery and dependency removals. I mentioned composition yesterday. Symfony 4 will lever those smaller dependencies to help you compose your applications.

Want to use forms? Require symfony/form. Want to use the PHP built-in server? Require symfony/web-server-bundle. Progressive enhancement. Add dependencies only when needed.

Coupled with auto-configuration, it is very powerful. Don’t need the built-in web server anymore? Remove the symfony/web-server-bundle package. Symfony takes care of un-configuring the bundle.

This is a very simple example, but there is more. Let’s illustrate the power of this new paradigm with SensioDistributionBundle, a bundle required by default in Symfony Standard Edition.

Don’t you think that requirement checks are currently weirdly implemented? Files are copied from the bundle to the Standard Edition on release. You are responsible for removing them before deploying (especially web/config.php).

The whole logic has been moved to symfony/requirements-checker. Want to check requirements? Add the package with Composer. Run the scripts. Fix any issues. Uninstall the package when done. Files are added and removed automatically.

The other main feature of SensioDistributionBundle is to execute some commands when you run composer install or composer update: they manage the bootstrap file (which is not needed anymore as of PHP 7), clear the cache, and install assets. Feels like hardcoded logic (have a look at the Sensio\Bundle\DistributionBundle\Composer\ScriptHandler::* call in your project's composer.json file). I reworked the concept for Symfony 4 in an extensible way. You can hook into it and add your own commands and logic.

There won’t be a SensioDistributionBundle version compatible with Symfony 4. We don’t need one. You can think of Symfony Flex as being the successor of it. A simpler and more powerful version of it.

Bundle-less Applications

When we wrote the first version of the Symfony best practices, we had a long debate about promoting “one bundle applications” vs “bundle-less applications”. We decided to go with a single AppBundle bundle to avoid a too-big disruption, but also because Symfony was not ready to support bundle-less applications as a first class citizens. But we worked hard during the last few months to make sure that Symfony 4 can embrace bundle-less applications.

So Symfony 4 will recommend and generate bundle-less applications. No more bundle for your code, just use App\ as a namespace for any class under src/. It reduces the perceived complexity. It also makes your code feels more decoupled from Symfony. I don't think applications should decouple 100% of its code from the underlying framework, but as of Symfony 3.3, a lot of features help you just do that.

Bundle-less applications is just one of the best practices changes for Symfony 4. Best practices is the topic for the next post.

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Fabien Potencier

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