What is the role of the Symfony kernel in an application?

The Symfony kernel is the heart of a Symfony application, responsible for handling requests and responses. It serves as the entry point for all HTTP requests and manages the entire lifecycle of the application.

To understand its role, consider the following steps:

1. Bootstrapping: The kernel initializes the application and loads necessary configurations.
2. Handling Requests: It listens for incoming HTTP requests.
3. Routing: The kernel delegates the request to the appropriate controller based on the routing configuration.
4. Response Generation: After the controller processes the request, the kernel sends the response back to the client.

For instance, a basic kernel can be created as follows:

use Symfony\Component\HttpKernel\Kernel;  
class MyKernel extends Kernel {  
    protected function configureContainer(ContainerBuilder $container) {  
        // Configure services here  
    }  
}