Set Node + Blackbox exporter listen address
I don't know whether this should go in. (Probably not.)
Upside: I feel making these services listen on the right interface is better than relying on firewall rules only.
Downside: I am afraid this will lead to not so great failure modes when the VPN is down when the exporter comes up, for example. Also, my code for finding the VPN interface IP is questionable at best.
I would err on the side of caution and leave this out, but I am interested to hear what you guys think.