If you want two identical servers connecting to their local MySQL instances, you need a way of deciding which one is the production server. There are a number of solutions for that, including
- Setting up a reverse proxy, as you mention, but then, your proxy itself becomes a SPOF,
- Using a floating IP, also known as a failover IP, but this only works if your host supports it. Cloud providers typically support them, as well as some bare metal server providers.
There is nothing specific to Go as far as I know.