> You'd use it where you'd use REST/API/JSONRPC/

Not really. You'd use it for inter service communication but can't really use it in the browser (see grpc-web)

At my workplace we use gRPC for inter service and client service communication from a VueJS SPA. It took some effort but is working really great right now. A colleague wrote a blog post (actually entire series) about it: https://stackpulse.com/blog/tech-blog/grpc-web-using-grpc-in...

Does gRPC bring fexibility and discoverability like GraphQL?

You can enable reflection API (but must compile your server with it) - e.g. it exposes some well known end-point, which when asked can return you back the other end-points available (services), and then asking each end-point service can return each method - and then for each method - what it takes (assuming as "proto") and returns, also what kind is (one shot, bidi, etc.)

So not the same as GraphQL, as you are not asking about resources/objects, but rather inspecting what can be called and how.

I have not used GraphQL in practice so I can't directly compare them.

What I can say is that in terms of flexibility, protobufs by nature provide us with forward and backward compatibility. We can easily add new fields and eventually deprecate old ones, evolving the API similarly to GraphQL.

Apparently, gRPC also has some introspection capabilities like GraphQL (since again you have a clear protobuf schema) but I have never used them in my clients, and perhaps they are not as baked into the system as in GraphQL.

Thanks for the explanation!

Why wouldn't it be enough to use REST with a protobuf media type?

There is some support for that [1]. I prefer to use native binary gRPC because:

1) REST verb/code mapping is too arbitrary for my taste, I prefer explicit verbs in RPC method names and error codes explicitly designed for RPC [2] and ones that will not be accidentally thrown by your HTTP proxy thereby confusing your client

2) REST stream multiplexing over a minimum amount of TCP connections is difficult to do, I trust the gRPC authors to have done their homework better than the average HTTP library. In addition, you can multiplex multiple gRPC bidirectional streams over a single TCP connection, which is something you can't do over plain HTTP without resorting to websockets.

[1] - https://cloud.google.com/endpoints/docs/grpc/transcoding

[2] - https://github.com/grpc/grpc/blob/master/doc/statuscodes.md

Good points.

Thanks again!

REST is a poor model for many scenarios, most obviously when the client and server aren’t dealing with resources or aren’t trying to maintain a shared model of state. A distributed database consensus protocol is a good example of the former, and an application server streaming metrics to a metric aggregation server is a good example of the latter.

gRPC's HTTP2 transport is basically this, out of the box. You don't need to manually manage routes, handlers, headers, status codes, etc.