First, I would caution against exposing services to the internet. It would be far better to leave everything behind a VPN that only you or trusted peers can access.

Past that you can use tools like OSSEC, Snort, and fail2ban.

Have a look at Tailscale for your devices, this will prevent you from having to expose anything to the Internet, but rather having it behind your own VPN solution. Tailscale is the kinda service that is stupid easy to get going with too. HIGHLY recommend it!

Ayy, nice work getting started down the selfhosting route! Start by remembering that security is a maturity process. To find out if you’re doing the right things at the right time, ask yourself:

• Do I know it needs to be done
• Have I done enough (this day, week, etc)
• Do I have it to give

If you’re just one person and it’s a self-hosted home setup, remember you can’t patch all the things all at once. Asking yourself regularly if you maturing your environment over time is essential. Do a little work each week and you’ll make good progress.

When I think of security, I think of a few things

Authentication & Access - each system should have just enough accounts with just enough permissions to get work done. Change default passwords. Make them long and unique. Use MFA whenever possible (often impractical for self-hosted; cut yourself slack when this is the case!). A note on logging - if you can, while you’re doing this homework, check how long it saves logs. Shoot for keeping logs longer if possible; I like 30 days, but you might want more. Also make sure you have a time server, or at least that you’re getting accurate time stamps. If something weird happens and you’re investigating, having timestamps on logs that line up and make sense helps you recreate what happened, so you can decide if you need to wipe something and reload it.

Patching - automated scanning of your stuff for vulns would be fantastic if you’re interested in going that route, but a Saturday morning checklist to run updates on everything works too.

Attack Surface Management - if you’re not sure you’re exposed, scanning externally can be a big help. I have a Racknerd server ($40/yr, it’s amazing) in San Diego and I periodically run scans of my home network to see what’s forwarded. This is using nmap, although I could also use a free version of Nessus Essentials on there. This gives me an idea of what I look like from outside my network.

Inventory - do you know what you have, and what’s it doing? Even a pencil drawing of your network, IP addresses, and services they have can come in super handy. While big orgs have an index of critical data and where it’s stored, just knowing what containers are running on which VM or physical box can help if stuff goes sideways. I redraw mine periodically, yes it’s hand drawn because it’s fast and does the job lol. Do what works for you, though, to keep an inventory of your stuff. You need to know what you have, what it does, and where it’s supposed to be going.

Thanks to everyone who took the time to answer. How do I check if my server has been accessed?

It’s not a simple task, so I won’t list many specifics, but more general principles.

First, some specifics:

• disable remote root login via ssh.
• disable password login, and only permit ssh keys.
• run fail2ban to lock people out automatically.

Generally:

• only expose things you must expose. It’s better to do things right and secure than easy. Exposing a webservice requires you to expose port 443 (https). Basically everything else is optional.
• enable every security system that you don’t have reason to disable. Selinux giving you problems? Don’t turn it off, learn how to write rules to let your application do the specific things it needs. Only make firewall exceptions where needed, rather than disabling the firewall.
• give system users the minimum access they require to function.
• set folder permissions as restrictively as possible. FACLs will help, because it lets you be much more nuanced.
• automatic updates. If you have to remember to do it, it won’t happen. Failure to automate updates means your software is out of date.
• consider setting up a dedicated authentication setup like authellia or keycloak. Applications tend to, frankly, suck at security. It’s not what they’re making so it’s not as good as a dedicated security service. There are other follow on benefits.
• if it supports two factor, enable it.

You mentioned using cloud flare, which is good. You might also consider configuring your firewall to disallow outbound connections to your local network. That way if your server gets owned, they can’t poke other things on your network.

You just don’t and pray for the best /j

Set up a weekly or at least monthly reminder to check for updates. That’s the most important thing to do. Outdated packages may have known security vulnerabilities.