Is it legal for me to use HA setup and maintenance as a product

I’ve read a few posts here that cover around this topic but my question is as straight forward as possible, can I offer a system that uses HA as the main setup and support it for a charge,

Not asking about the stability experience I understand it is constantly changing and has many breaking changes with every update

Just want to know:

A: is it legal to sell
B: how obligated are HA to remain an open source system (say they are purchased by google, what will happen to my business?)

Thanks in advance :pray: