This single kernel approach is a convenient default provided by the Symfony

Standard edition, but Symfony applications can define any number of kernels.

This is useful to execute the same application using a different configuration

and a different set of bundles for each kernel:

* An application that defines an API could create an ``ApiKernel`` to not have

to load all the bundles enabled in the regular web application. This will

improve the API performance;

* A bundle that doesn't allow multiple instances can define multiple

configurations in different files loaded by each kernel.

Whereas:doc:`environments</configuration/environments>` execute the same

application with different configurations, kernels can execute different parts

of the same application.

These are some of the common use cases for creating multiple kernels:

* An application that defines an API could define two kernels for performance

reasons. The first kernel would serve the regular application and the second

one would only respond to the API requests, loading less bundles and enabling

less features;

* A highly sensitive application could define two kernels. The first one would

only load the routes that match the parts of the application exposed to the

public. The second kernel would load the rest of the application and its

access would be protected by the web server;

* An application that uses a bundle which doesn't allow multiple instances could

define two identical kernels to define a different bundle configuration for

each of them.

Adding a new Kernel to the Application