I'm surprised many people don't understand your comment - I had the same thoughts. gRPC provides a very nice way to describe event driven microservices using their "stream" keyword. It allows the implementation to be async, blocking, or future based. You get access to a very rich ecosystem such as bazel's grpc \ proto rules, junit rules, grpc-web for streaming to the browser, out of the box support from istio / envoy, etc.