A service requires two configuration files, which are XML files:
The service definition file describes the service model. It defines the roles included with the service and their endpoints, and declares configuration settings for each role. The default extension for the service definition file is .csdef.
The service configuration file specifies the number of instances to deploy for each role and provides values for any configuration settings declared in the service definition file. The default extension for the service configuration file is .cscfg.
For optionally using a virtual network or configuring diagnostics, you can use:
The network configuration file, which describes Virtual Network configuration settings. The default extension is .netcfg.
The diagnostics configuration file, which describes the values that are used to initialize the Diagnostics Monitor. The name of the file is diagnostics.wadcfg.
This reference describes the schema for each file.