[zie]

The problem here is, it depends on WHY you are rate limiting. If it's just to balance so you don't overload your backends, then absolutely this is a great way to do it.

If however you are trying to limit client(s) because the service is an authentication gateway for instance, then you want to limit user/pass requests to X number then concurrency limiting isn't a good way to do that.

So you may need both, depending on your use-cases, so it's not a one-size fits all solution.

[bogomipz]

What is the use case for your second example? I am not following.

Wouldn't that just be rate limiting by client IP though?

[zlynx]

I heard about a case where someone built a phone app backend without rate limiting. Someone found this hole and successfully attacked 70,000 accounts by running password dictionary cracks against the authentication API.

Modern distributed systems are simply too fast and users are too dumb with picking passwords to allow unlimited password attempts.

[zie]

Well you can rate limit via a lot of things, definitely by IP is a good idea, but for ipv6, you typically want to limit by blocks(since every ipv6 user currently usually gets a full block of IP's), but you also probably want to also limit by username, i.e. if you keep trying to login as user 'root', you only get 3 attempts/minute or something.

After X attempts via the same IP, you can block/ban that IP via a FW rule/etc for say 5 mins. or 30m, or whatever.

It all depends on your security posture, you could go crazy and actually lock the account after 3 failures, but then you hand bad people a free DDOS... so you have to be careful about doing that.. But you could soft-lock and require a correct password and an email address verification after X failed attempts(i.e. correct login, plus they have to click a link in an email).

Anyways, see what I'm saying here? Authentication access is something you really want to get right, and it's a complicated topic.

[dboreham]

>Wouldn't that just be rate limiting by client IP though?

This won't defeat an adversary with a botnet.

[heavenlyblue]

But this is not something you deal with a rate-limiter. By your logic, then a sufficiently large botnet would dwarf any live traffic whatsoever, implying you’d probably want to filter them on network level instead.