If a host was deployed using vSphere Auto Deploy, you can use vSphere Auto Deploy to reprovision the host with a new image profile that contains a different version of ESXi. You can use vSphere ESXi Image Builder to create and manage image profiles.
If you upgrade the host to use an ESXi 6.0 or later image, the vSphere Auto Deploy server provisions the ESXi host with certificates that are signed by VMCA. If you are currently using custom certificates, you can set up the host to use the custom certificates after the upgrade. See vSphere Security.
The vSphere Auto Deploy server is automatically upgraded if you upgrade the corresponding vCenter Server system. Starting with version 6.0, the vSphere Auto Deploy server is always on the same management node as the vCenter Server system.