> Security through obscurity isn't security. It could be a method to reduce noise, but by doing so, you also have less eyes to watch over. If you'd pay for a blackbox pentest, and the pentester doesn't find your OpenSSH server running on a different port, then that doesn't tell you anything about the security of your OpenSSH server. In a whitebox pentest, they'd know about it beforehand. So, do you want to test the security of your OpenSSH server, yes or no?
If your pentester can't find your sshd on a different port: 1) that is prima facie evidence that it works for a similar (low) skill level of attacker, and 2) you should fire that pentester. I'll leave the reasoning as an exercise for the reader.
> I don't allow traffic from any IPs allocated to China or Russia, among a couple of other countries, and I don't feel like I am missing out.
Now yer talkin'! As a blanket policy, if you have no valid users outside of your own nation and no expectation that will change, why not block everybody who isn't local?
(Of course, that just means any Russians and Chinese who do manage to attack you may be actual spooks, so if that happens you're pwned anyway. ;-) But you'll have cut down on your security logs considerably.)
> Another one is port knocking. Anyone who has read access over the network between client and server can figure out the port knocking process, including a hostile actor who does a MITM (with for example a rogue WiFi AP).
While I appreciate the fact that you're thinking outside of the typical box with regard to threat modelling, such an MITM attack is quite a few orders of magnitude more intentional of an attack than the rest of the crap the average systems/security admin has to deal with. In the case of a non-targeted (ie. not against a specific user or org) you're looking at a malicious network operator, which is far more sophisticated than 99.x% of the bulk scanning and attacks most admins see. In the case of a targeted attack we're talking about funded and probably successful organized crime at the very least, and possibly even nation-state intel orgs. Only motivated, professional attackers tend to get off their butts and travel to a different location to conduct an operation like that.
Kudos for recognizing such a problem, but using that as an excuse not to employ a powerful security technology such as port knocking is rather throwing the baby out with the bathwater. If you're going to be that defeatist, just airgap the system and be done.
Now, if you are willing to go through the effort of whitelisting IPs (which, I suspect, you haven't done yet, or you'd already loathe doing it and not recommend it), the sane way of going about that is to set up a VPN and whitelist the IP of the gateway. Otherwise you've opened up an administrative can of worms that is bad indeed. Nobody wants to have to keep track of Joe Blow's home IP address, which changes weekly at least, for some whitelist.