yoo! https://www.slideshare.net/jdwyah/diy-heroku-using-amazon-ec... does have a bit of a pretty picture, but the basic idea is:

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.

(details in https://www.ratelim.it/documentation/safety)

It's worth noting that with either of these you can cache aggressively in the clients whenever the limits have gone over. Both the clients https://github.com/jdwyah/ratelimit-ruby https://github.com/jdwyah/ratelimit-java do that for you.