Which file determines the location of the installation script during a scripted upgrade?

I disagree, the answer is ks.cfg,

https://pubs.vmware.com/vsphere-60/index.jsp#com.vmware.vsphere.install.doc/GUID-A33C4CAB-18EE-4C8C-A55D-8AD7E8042BFA.html

“ks=file://path” – Performs a scripted installation with the script at path.

The installation script is located in boot.cfg. The boot loader configuration file boot.cfg specifies the kernel, the kernel options, and the boot modules that the mboot.c32 boot loader uses in an ESXi installation.

PXE Boot the ESXi Installer Using gPXE
You can PXE boot the ESXi installer using gPXE.
See also About Installation and Upgrade Scripts and About the boot.cfg File
Prerequisites
Verify that your environment has the following components:
■
The ESXi installer ISO image downloaded from the VMware Web site
■
HTTP Web server that is accessible by your target ESXi hosts
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DHCP server configured for PXE booting: /etc/dhcpd.conf is configured for client hosts with a TFTP server and the initial boot file set to gpxelinux.0/undionly.kpxe. See Sample DHCP Configuration.
■
Server with a hardware configuration that is supported with your version of ESXi. See the Hardware Compatibility Guide at http://www.vmware.com/resources/compatibility/search.php.
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gPXELINUX
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(Optional) ESXi installation script. See About Installation and Upgrade Scripts.
Use a native VLAN in most cases. If you want to specify the VLAN ID to be used with PXE booting, check that your NIC supports VLAN ID specification.
Procedure
1
Copy the contents of the ESXi installer ISO image to the /var/www/html directory on the HTTP server.
2
Modify the boot.cfg file with the information for the HTTP server.
Use the following code as a model, where XXX.XXX.XXX.XXX is the HTTP server IP address. The kernelopt line is optional. Include that option to specify the location of the installation script for a scripted installation.

title=Loading ESX installer
kernel=http://XXX.XXX.XXX.XXX/tboot.b00
kernelopt=ks=http://XXX.XXX.XXX.XXX/esxi_ksFiles/ks.cfg
modules=http://XXX.XXX.XXX.XXX/b.b00 — http://XXX.XXX.XXX.XXX/useropts.gz — http://XXX.XXX.XXX.XXX/k.b00 — http://XXX.XXX.XXX.XXX/a.b00 — http://XXX.XXX.XXX.XXX/s.v00 — http://XXX.XXX.XXX.XXX/weaselin.t00 — http://XXX.XXX.XXX.XXX/tools.t00 — http://XXX.XXX.XXX.XXX/imgdb.tgz — http://XXX.XXX.XXX.XXX/imgpayld.tgz
3
gPXE boot the host and press Ctrl+B to access the GPT menu.
4
Enter the following commands to boot with the ESXi installer, where XXX.XXX.XXX.XXX is the HTTP server IP address.
dhcp net0 ( if dchp is not set)
kernel -n mboot.c32 http://XXX.XXX.XXX.XXX/mboot.c32
imgargs mboot.c32 -c http://XXX.XXX.XXX.XXX/boot.cfg
boot mboot.c32