In the past two weeks I set up a new VPS, and I run a small experiment. I share the results for those who are curious.
Consider that this is a backup server only, meaning that there is no outgoing traffic unless a backup is actually to be recovered, or as we will see, because of sshd.
I initially left the standard "port 22 open to the world" for 4-5 days, I then moved sshd to a different port (still open to the whole world), and finally I closed everything and turned on tailscale. You find a visualization of the resulting egress traffic in the image. Different colors are different areas of the world. Ignore the orange spikes which were my own ssh connections to set up stuff.
Main points:
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there were about 10 Mb of egress per day due just to sshd answering to scanners. Not to mention the cluttering of access logs.
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moving to a non standard port is reasonably sufficient to avoid traffic and log cluttering even without IP restrictions
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Tailscale causes a bit of traffic, negligible of course, but continuous.
Tailscale is built on top of wireguard. It just manages all the hassle of configuring it. In my case it was a godsend as I have like 10 devices all roaming and scattered across multiple countries. It'd be a massive headache to type down IPs and whatnot every time one changes networks.
Thanks for enlightening me on that aspect, setting that up with just Wireguard would indeed be a pain or outright impissible without additional tools (e.g. for UDP hole-punching), maybe I should also consider it :)