'Rate limit' of new sign-ups from the same IP address

[rodti]

I run two instances with open registration. I regularly see cases of (presumably automated) multiple account sign-ups from the same IP address, which with very few exceptions are spam.

My suggestion is to implement a check against IP address when a new user attempts to register. If that IP address has been used to sign up for another account within a reasonable time frame (1 hour? 12 hours?) then the request is denied, or placed in the registration approval queue.

Motivation

This proactive check would prevent large numbers of spambots entering the fediverse before moderators spot these accounts or receive reports relating to them, and reduce the effort required to moderate/administer an instance as currently these accounts have to be individually suspended which is an onerous process.

I'd previously raised this suggestion, however I believe this one is a more elegant solution.

[Gargron]

Create an IP rule with severity “limit sign-ups” to have them be placed in the moderation queue

[rodti]

Create an IP rule with severity “limit sign-ups” to have them be placed in the moderation queue

That's fine in some scenarios. Here the damage is already done by the time I spot them. 30 user accounts from one IP address, then more from another, and another, and so on. By the time I even realise this has happened there's a huge mess of accounts I need to suspend one by one.

The only solutions I can see are to proactively prevent multiple rapid sign ups from a single IP, or to set my instance to approval-only or closed registration, which seems a shame.