You're welcome

Anyways, you might have forgotten that a backup link cannot use back the same domain.

Let's say you have domain.com pointing to:
ns1.server1.com
ns2.server1.com

And you setup a subdomain, support.domain.com to point to Server 2. If server 1 is down, when visiting support.domain.com, the redirection will not work as well. The reason is because the domain is still pointing to Server 1 and it 'lost contact' if Server 1 is not responding and failed to redirect visitors to Server 2.

For your case, I would suggest getting another domain just for backup forum.

Thank you.