Obsidian is not open source but i also think it’s pretty neat.

https://github.com/slidesk/slidesk

remote kvm if you are relying on a box that no longer has a network connection you are SOL and need something that can power cycle the box.

Primary and secondary dns is not a thing. There is no priority for DNS. Depending on the device it will use ether address and will only try the other on failure.