A deploy rule is created to deploy a chosen ESXi image onto a server or group of servers chosen based on a supported pattern. Without a deploy rule, Auto Deploy server will not be able to associate an ESXi image with a server to boot.
The pattern used to choose a server for deploying ESXi uniquely identifies the machine or a group of machines. The pattern can be an IPv4 address range, a MAC address, hardware vendor name, asset tag, domain name, server model, serial number, and so on.
Prior to creating a deploy rule, it is a prerequisite to connect to the vCenter server to which Auto Deploy is registered to, using the Connect-VIServer cmdlet. Unless this is done, you will not be able to create a new deploy rule.