How would an instance block an IP without storing IPs?
They could be blocking entire IP ranges. So they wouldn’t have to store specific IPs. I’m not in the hosting industry but I would imagine there are groups tracking the CIDR blocks (IP ranges) that VPN providers use for their exit nodes. If such a list exists, a host could simply subscribe to accept whatever updates occur to those lists and implement the block for them.
They could be blocking entire IP ranges. So they wouldn’t have to store specific IPs. I’m not in the hosting industry but I would imagine there are groups tracking the CIDR blocks (IP ranges) that VPN providers use for their exit nodes. If such a list exists, a host could simply subscribe to accept whatever updates occur to those lists and implement the block for them.