Automated config deployment has a number of use cases, from making OEM installations to transplanting configs from a failed router to new hardware.
While in virtual environments and local network it's fairly easy to retrieve configs over a network securely (in terms of authenticity and confidentiality), if the network admin has taken measures against address spoofing, over a WAN or another insecure network it's problematic. The only way to do it is to include trusted certificates and keys in the image, but it means the image must be custom built, and few people will want to do it.
Deploying configs from a removable drive is a relatively easy and secure option that would allow e.g. branch office personnel or field service technicians to end up with a functional VyOS right after installation.
Copying just the config makes little sense, since it often needs additional files such as keys and certs. The sensible approach is to copy the whole /config dir, together with /config/auth, /config/user-data etc.
The correct removable drive can be identified through udev checks, run+="/somepath/check_if_it_contains_configdir"
The configs can be stored in a specific dir, such as /vyos-configs
Specially for field service technician jobs, we can check if there is more than one subdir and ask which one to use.
Config dirs will be checked by looking if there's config.boot file and if it has a VyOS version string.
Support you created a USB stick with the following directory structure:
/ /vyos-configs /office config.boot /warehouse config.boot
Then you plug it in a box and start installing VyOS:
... Do you want to deploy configuration from a removable drive? [y/N] y Removable drive contains the following configurations: office, warehouse Select the configuration you want to use: warehouse ...