proxy

README

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 exaple 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, grpc.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.
            return grpc.DialContext(ctx, "api-service.staging.svc.local", grpc.WithCodec(proxy.Codec()))
        } else if val, exists := md[":authority"]; exists && val[0] == "api.example.com" {
            return grpc.DialContext(ctx, "api-service.prod.svc.local", grpc.WithCodec(proxy.Codec()))
        }
    }
    return nil, grpc.Errorf(codes.Unimplemented, "Unknown method")
}

Then you need to register it with a grpc.Server. The server may have other handlers that will be served locally:

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

License

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

Documentation

Overview

Package proxy provides a reverse proxy handler for gRPC.

The implementation allows a `grpc.Server` to pass a received ServerStream to a ClientStream without understanding the semantics of the messages exchanged. It basically provides a transparent reverse-proxy.

This package is intentionally generic, exposing a `StreamDirector` function that allows users of this package to implement whatever logic of backend-picking, dialing and service verification to perform.

See examples on documented functions.

Index

• func Codec() grpc.Codec
• func CodecWithParent(fallback grpc.Codec) grpc.Codec
• func RegisterService(server *grpc.Server, director StreamDirector, serviceName string, ...)
• func TransparentHandler(mq mq.MQ, director StreamDirector) grpc.StreamHandler
• type StreamDirector

Functions

func Codec

func Codec() grpc.Codec

Codec returns a proxying grpc.Codec with the default protobuf codec as parent.

See CodecWithParent.

func CodecWithParent

func CodecWithParent(fallback grpc.Codec) grpc.Codec

CodecWithParent returns a proxying grpc.Codec with a user provided codec as parent.

This codec is *crucial* to the functioning of the proxy. It allows the proxy server to be oblivious to the schema of the forwarded messages. It basically treats a gRPC message frame as raw bytes. However, if the server handler, or the client caller are not proxy-internal functions it will fall back to trying to decode the message using a fallback codec.

func RegisterService

func RegisterService(server *grpc.Server, director StreamDirector, serviceName string, methodNames ...string)

RegisterService sets up a proxy handler for a particular(详细的) gRPC service and method. The behaviour is the same as if you were registering a handler method, e.g. from a codegenerated pb.go file.

This can *only* be used if the `server` also uses grpcproxy.CodecForServer() ServerOption.

func TransparentHandler

func TransparentHandler(mq mq.MQ, director StreamDirector) grpc.StreamHandler

TransparentHandler returns a handler that attempts to proxy all requests that are not registered in the server. The indented use here is as a transparent proxy, where the server doesn't know about the services implemented by the backends. It should be used as a `grpc.UnknownServiceHandler`.

This can *only* be used if the `server` also uses grpcproxy.CodecForServer() ServerOption.

Types

type StreamDirector

type StreamDirector func(ctx context.Context, fullMethodName string) (context.Context, *grpc.ClientConn, error)

StreamDirector returns a gRPC ClientConn to be used to forward the call to.

The presence of the `Context` allows for rich filtering, e.g. based on Metadata (headers). If no handling is meant to be done, a `codes.NotImplemented` gRPC error should be returned.

The context returned from this function should be the context for the *outgoing* (to backend) call. In case you want to forward any Metadata between the inbound request and outbound requests, you should do it manually. However, you *must* propagate the cancel function (`context.WithCancel`) of the inbound context to the one returned.

It is worth noting that the StreamDirector will be fired *after* all server-side stream interceptors are invoked. So decisions around authorization, monitoring etc. are better to be handled there.

See the rather rich example.