I'm currently running both a home server and a VPS. The former is not reachable through the internet, only through vpn. The latter hosts public services.
The VPS is regularly cutting it very close with storage and today I messed up and crashed the whole stack trying to make an impromptu backup. Lesson learned: we need more storage! I could just rent more storage but just today I updated my home server with 16 TB of raid 1 enterprise HDDs.
So I thought I could maybe do a (wireguard) VPN tunnel directly to some storage service that I host on my homeserver. The upload is not great but realistically I dont need much. The important stuff stays on the VPS. Mainly videos, pictures and other stuff that doesnt get accessed a lot should go there. The rest should be "cached" at the VPS.
I would have to host wireguard on a server port, only have it access one folder which doesnt contain anything important, forward the port on the router and have the vps have the keys. Even if someone gets into the VPS and steals the keys, they only get that one file storage folder.
Has anyone done this? Are there services that do this or do I just host wireguard and thats it?
You should consider reversing the roles. There's no reason your homelab cannot be the client, and have your vps be the server. Once the wireguard virtual network exists, network traffic doesn't really care which was the client and which was the server. Saves you from opening a port to attackers on your home network.
You can also configure your server to only accept traffic on the VPN port coming from your home IP address if you've a static one. Or.. only allow incoming connection from your country (https://wiki.nftables.org/wiki-nftables/index.php/GeoIP_matching). This will provide you an extra layer of security.
Either way don’t be afraid to expose the Wireguard port because an attacker won’t even know there’s something listening on that port as it will ignore any piece of traffic that isn’t properly encrypted with your keys;
Tbh I sometimes sshfs mount a vps onto a home machine but doing it the other way around doesn't seem worthwhile. The idea of a vps is that it's in a data center, has tons of bandwidth, backup power, you can set up a failover scheme if you need high availability, etc. Stuff like media is on your home server so you can use it locally, and maybe it's backed up remotely just in case, but doesn't need to be live mounted. That said, I'm used to home internet being unreliable compared to VPS, so mounting it to a vps sounds flaky.
If you want more storage on your vps, just get a bigger one, I would say. Or if you want tons of remote storage, get something with better connectivity.
For the backup scenario in particular, it makes sense to pipe them through right to the destination. Like, tar -zcv somefiles | ssh $homeserver dd of=backup.tar.gz, or mysqldump | gzip -c | ssh $homeserver dd of=backup.sql.gz. Since it's basically a download from your home server's perspective it should be pretty fast, and you don't need temporary space at all on the VPS.
File caching might be a little tricky. You might be best self host some kind of object storage and put varnish/NGINX/dedicated caching proxy software in front of it on your VPS, so it can cache the responses but will ultimately forward to the home server over VPN if it doesn't have it cached.
If you use NextCloud for your photos and videos and stuff, it can use object storage instead of local filesystem, so it would work with that kind of setup.
How exactly did you manage to make it available without forwarding a port? If the server is behind your routers with no way through, a vpn shouldn’t reach it either.
Edit: Not talking about a "privacy VPN", but an actual VPN that lives up to the name "Virtual Private Network", where you are connecting to the private network you wish to access.
You could self-host a S3-compatible storage bucket with something like MinIO or Garage.
S3 backends are available in a lot of software and it's kinda made for a similar use-case. I don't know which projects have caching available in a way that aligns with your setup. But I found these two being easy to set up.
I haven't done it yet but I plan on doing it. But I never bothered with a VPN and just expose a ssh port. So I plan just to mount a directory with sshfs.
My solution is to use Rathole. I rent a wildly cheap (2 core, 4GB memory) VPS and basically just run Traefik there. Then I use Rathole to make some services hosted on my desktop available to Traefik.
I like this solution better than Wireguard for my application. It reduces attack surface to services you've explicitly set up, rather than a full data layer trunk between your machine and a potential malicious actor.