The host's identity a licence names: the SHA-256 of its machine id file, lowercase hex.

On Linux that file is /etc/machine-id. Inside a container that path holds the image's id, which every container of the image shares, so an on-prem install bind-mounts the host's file into the container read-only and passes its path here. The hostname changes on every recreate, and /sys/class/dmi/id/product_uuid is readable by root alone, so neither serves.