I wrote Locomotor[0] to automate the translation of Python code to Lua for Redis. Basically, you add an annotation to a function and the first time the code executes, it's converted to Lua and shipped to the server. You can see an example here[1]. It's far from foolproof and many Python language constructs have not been implemented, but it can handle some relatively complex code.
I'm guessing it would look something like this... I omitted checking if the token is in the 1 minute window. It returns false if the user has reached the rate limit, true if the user has more tokens left. If the user has tokens left, it decrements the token the user has left before returning true.
local id = "user_1"
-- Get the number of tokens the user has left
local tokens = redis.call("HGET", id, "tokens")
if tokens = 0 then
-- User has no tokens left
return false
else
-- User has tokens left, decrement token count
redis.call("HINCRBY", id, "tokens" -1)
return true
end
Redis lua scripts block while they are running, so the two redis calls here cannot be interleaved with other reads, as in the token bucket example from the article.
agreed. I was a bit leery of diving into Lua as I was building http://ratelim.it but it really expands Redis's capabilities dramatically and was easy enough to add.
My apps all write the lua into redis and store the hash when they boot up. Duplicative, but means everybody is on the same page and it's easy to store the lua in the main codebase.
For each rate limit you can choose to be in one of two modes:
1) Redis with a backing store of DynamoDB aka BestEffort since there are failure modes where you could lose an update. In this mode everything expects to happen in Redis, but if we don't find your limit there we check Dynamo. Writes are asynchronously persisted to Dynamo.
2) Token Buckets straight in DynamoDB. This is our Bombproof mode.
