First you’ve got to determine where threats can come from, then which surfaces are vulnerable and eventually the reach. In short what I mean:

SSH port (default 22) is high on the threat encounter level. Lots of bots try to scan every host they can find for an open SSH port. The risk is high because this is a doorway to your network. There’s honestly no good reason to have port 22 open to your home. Get [tailscale vpn] (tailscale.com). There are alternatives, I use tailscale, it’s great.

When youre hosting apps, they can also be vulnerable. Keep them updated and you’ll mostly be fine. There are levels of security. Super super secure is creating seperate networks for these apps so they can’t access others. Bit much imo. Use non-rooted docker, enough of a sandbox.

In the end you’re a small fish in a big pond, not saying you should be a cowboy but with a few decent measures you should be OK.

Tl;dr

• don’t open port 22
• use a VPN (tailscale)
• update apps
• non-rooted docker

What's wrong with exposing port 22? I have password authentication disabled, ssh keys only. Isn't that secure enough?

I do as well on a non-standard port, although that doesn't really provide any extra security. I found ssh only login acceptably secure personally, but it's definitely less secure than tailscale which can operate with 0 open ports. The risk would be from os/sshd vulnerabilities that can be exploited. As long as you keep the router up to date it should be safe enough.

Why would you expose SSH on a production server?
Hosting several dockerized apps for friends since years. Only 80/443 proxy ports are open. Apps are secured with 2FA and monitored by fail2ban + kept up-to-date. Never had any issue.

It's for the chance that I need to administer my cluster when I am not on my LAN. I can set up a port forward to the externally accessible port and everything works as normal like I'm on my LAN. Non-default port, password auth disabled, ssh with root disabled (so you have to have my user and ssh key) and limited ssh connection attempts before ban. I can toggle it on or off with a check box on my router. Yes, I understand there are other ways that are even more secure, yes I understand the risks, but for my circumstances this was a good balance of convenience and security. I've also never had an issue :).

Add VPN and you made the best out of it :)