I'm not OP, but the main parallel is a well defined schema of communication between the services using different underlying technologies. SOAP is in my experie

I'm not OP, but the main parallel is a well defined schema of communication between the services using different underlying technologies. SOAP is in my experience really hard to use and get right, compared to protobufs that bring well understandable set of primitives and intuitive support in many languages. gRPC is a solid carrier for protobufs. Yes, gRPC has many cons (e.g. with undefined/nil values, etc.), but overall it has worked great for our usecases.