Redis Rate Limiter Pattern

Question

I am trying to use Redis Rate limiting patter as specified in https://redis.io/commands/incr under "Pattern: Rate limiter 1". But how can I scale this in case I want to do rate limiting across multiple servers. Like I have service deployed across 5 servers behind load balancer and I want total requests per api key across 5 servers should not cross x/sec. As per redis pattern I mentioned , the problem is that if I have my rate limiter running in multiple servers itself, then the two different request to two different rate limiter servers,can do "get key" at same time and read same value, before anyone updates it, which can probably allow more requests to go.How can I handle this?I can obviously put get in MULTI block, but I think it will make things a lot more slow.

Answer 1

INCR replies with the updated value. So it can be used as both write and read command.

FUNCTION LIMIT_API_CALL(ip)
ts = CURRENT_UNIX_TIME()
keyname = ip+":"+ts

MULTI
    INCR(keyname)
    EXPIRE(keyname,10)
EXEC

current = RESPONSE_OF_INCR_WITHIN_MULTI
IF current > 10 THEN
    ERROR "too many requests per second"
ELSE
    PERFORM_API_CALL()
END