The rate limit service is a Go/gRPC service designed to enable generic rate limit scenarios from different types of applications. Applications request a rate limit decision based on a domain and a set of descriptors. The service reads the configuration from disk via runtime, composes a cache key, and talks to the Redis cache. A decision is then returned to the caller. Envoy's data-plane-api defines a ratelimit service proto rls.proto. Logically the data-plane-api rls is equivalent to the ratelimit.proto defined in this repo. However, due to the namespace differences and how gRPC routing works it is not possible to transparently route the legacy ratelimit (ones based in the ratelimit.proto defined in this repo) requests to the data-plane-api definitions. Therefore, the ratelimit service will upgrade the requests, process them internally as it would process a data-plane-api ratelimit request, and then downgrade the response to send back to the client. This means that, for a slight performance hit for clients using the legacy proto, ratelimit is backwards compatible with the legacy proto.