fallback

problem

There is some problem in apache/dubbo-go when using multiple services under grpc protocol.

More detail, if you use multiple services under grpc protocol, only first service will be invoked successfully by consumers.

reason

• Because services use the same address (or location in codes), so the srv.Start(url) will be executed only once. Refer to openServer.
• Then the grpc server on provider side will register the first service. Refer to register in start.

how to fix

• Firstly, we cannot fix this problem directly because
  • the grpc server starts when the first service export and register
  • then other service cannot register after grpc server start
• Then we should find a way to register service after server start
  • apache/dubbo use a fallback method, refer to DubboHandlerRegistry implements HandlerRegistry
  • we can use UnknownServiceHandler in grpc/grpc-go/server.go, like mwitkow/grpc-proxy

disadvantage

• Because we implement unary rpc by streaming rpc, we cannot use unaryInt.