Known configurations
Known configurations, on the other hand, are specific pre-determined configurations for deploying an environment using ARM templates. These pre-determined configurations are known as T-shirt sizing configurations. Similar to the way a T-shirt is available in a pre-determined configuration such as small, medium, and large, ARM templates can be pre-configured to deploy a small, medium, or large environment depending on the requirements. This means that users cannot determine any random custom size for the environment, but they can choose from various provided options, and ARM templates executed during runtime will ensure that an appropriate configuration of the environment is provided.
So, the first step in creating a modular ARM template is deciding on the known configurations for an environment.
As an example, here is the configuration of a datacenter deployment on Azure:
