gRPC Proxy

gRPC Go Proxy server

Project Goal

Build a transparent reverse proxy for gRPC targets that will make it easy to expose gRPC services over the internet. This includes:

• no needed knowledge of the semantics of requests exchanged in the call (independent rollouts)
• easy, declarative definition of backends and their mappings to frontends
• simple round-robin load balancing of inbound requests from a single connection to multiple backends

The project now exists as a proof of concept, with the key piece being the proxy package that is a generic gRPC reverse proxy handler.

Proxy Handler

The package proxy contains a generic gRPC reverse proxy handler that allows a gRPC server to not know about registered handlers or their data types. Please consult the docs, here's an example usage.

Defining a StreamDirector that decides where (if at all) to send the request

director = func(ctx context.Context, fullMethodName string) (*grpc.ClientConn, error) {
    // Make sure we never forward internal services.
    if strings.HasPrefix(fullMethodName, "/com.example.internal.") {
        return nil, status.Errorf(codes.Unimplemented, "Unknown method")
    }
    md, ok := metadata.FromContext(ctx)
    if ok {
        // Decide on which backend to dial
        if val, exists := md[":authority"]; exists && val[0] == "staging.api.example.com" {
            // Make sure we use DialContext so the dialing can be cancelled/time out together with the context.
            conn, err := grpc.DialContext(
                ctx, 
                "api-service.staging.svc.local", 
                grpc.WithDefaultCallOptions(grpc.CallContentSubtype((&codec.Proxy{}).Name())),
                )
            return outCtx, conn, err
        } else if val, exists := md[":authority"]; exists && val[0] == "api.example.com" {
            conn, err := grpc.DialContext(
                ctx, 
                "api-service.prod.svc.local", 
                grpc.WithDefaultCallOptions(grpc.CallContentSubtype((&codec.Proxy{}).Name())),
                )
            return outCtx, conn, err
        }
    }
    return nil, status.Errorf(codes.Unimplemented, "Unknown method")
}

Then you need to register it with a grpc.Server. The proxy codec is automatically registered by importing the codec package. The server may have other handlers that will be served locally:

import codec "github.com/mwitkow/grpc-proxy/proxy/codec"

...

server := grpc.NewServer(
    grpc.UnknownServiceHandler(proxy.TransparentHandler(director)))
pb_test.RegisterTestServiceServer(server, &testImpl{})

License

grpc-proxy is released under the Apache 2.0 license. See LICENSE.txt.