With the vSphere Auto Deploy ESXi feature, you can provision and reprovision large numbers of ESXi hosts efficiently with vCenter Server.

When you provision hosts using the Auto Deploy feature, vCenter Server loads the ESXi image directly into the host memory. Auto Deploy does not store the ESXi state on the host disk. vCenter Server makes image profiles with ESXi updates and patches available for download through an image profile, and, optionally, the host configuration through a host profile. You can create host profiles using the vSphere Web Client. You can create custom image profiles with ESXi Image Builder CLI. See Using vSphere ESXi Image Builder CLI and vSphere Host Profiles.

The first time you install a host with Auto Deploy, the host PXE boots and establishes contact with the Auto Deploy server, which streams the image profile and any host profile to the host. The host starts, using the image profile, and Auto Deploy assigns the host to the appropriate vCenter Server system.

When you restart the host, the Auto Deploy server continues to provision the host with the appropriate image and host profile. To provision the host with a different image profile, change the rule that specifies the image profile and perform a test and repair compliance operation. This will propagate the change to all hosts that the rule specifies. This ability to propgate changes to multiple hosts makes Auto Deploy an efficient way to provision and reprovision large numbers of hosts, and to enforce compliance to a master ESXi image.

See Understanding vSphere Auto Deploy.