[achiang]

The problem that gRPC solves for you is versioning your messages between your services.

As your json payloads evolve, you're going to encounter pain trying to keep your services in sync, whether it comes in the form of writing parsing code to crack open payloads and do conditional error checking based on the version (and expected fields), or whether it comes operationally in how you actually deploy updates to running services.

[zepolen]

That's solved by protobuf, not grpc.