I find the idea of self-hosting to be really appealing, but at the same time I find it to be incredibly scary. This is not because I lack the technical expertise, but because I have gotten the impression that everyone on the Internet would immediately try to hack into it to make it join their bot net. As a result, I would have to be constantly vigilant against this, yet one of the numerous assailants would only have to succeed once. Dealing with this constant threat seems like it would be frightening enough as a full-time job, but this would only be a hobby project for me.
How do the self-hosters on Lemmy avoid becoming one with the botnet?
The other answer is already good but I answer more general.
Rate limiting. Do not allow as many requests as your CPU can handle but limit authentication requests. Like a couple requests per second already goes a long way.