In this new post to his site Tomas Votruba shows how to configure a Symfony application without using the bundle or extension configurations.
Symfony Flex is moving towards of bundle-less applications. That doesn't mean you should create a monolith code in /src as fast as possible, but rather control everything via .yaml and .env files. It's takes few steps to remove extension and move to import of services.yaml.
But how would you approach a simple task as setup a account number parameter?
For those not familiar with "no-bundle applications" in Symfony, he starts with a link to the SymfonyCast course listing out the main points. Following this he covers what changes in the service registration and what changes in the configuration (with code examples). He then provides some options including keeping the extension, setting the parameter manually and binding the parameter, favoring the last two on his list as more maintainable.