youtube/doorman: a solution for Global Distributed Client Side Rate Limiting. Clients that talk to a shared resource (such as a database, a gRPC service, a RESTful API, or whatever) can use Doorman to voluntarily limit their use (usually in requests per second) of the resource. Doorman is written in Go and uses gRPC as its communication protocol. For some high-availability features it needs a distributed lock manager. The purpose of Doorman is to apportion and distribute capacity to clients based on some definition of fairness.