grpc

brave-instrumentation-grpc

This contains tracing client and server interceptors for grpc.

The GrpcTracing class holds a reference to a tracing component, instructions on what to put into gRPC spans, and interceptors.

The client interceptor adds trace headers to outgoing requests. The server interceptor extracts trace state from incoming requests. Both report to Zipkin how long each request takes, along with relevant tags like the response status.

To enable tracing for a gRPC application, add the interceptors when constructing the client and server bindings:

grpcTracing = GrpcTracing.create(rpcTracing);

Server server = ServerBuilder.forPort(serverPort)
    .addService(ServerInterceptors.intercept(
        GreeterGrpc.bindService(new GreeterImpl()), grpcTracing.newServerInterceptor()))
    .build()
    .start();

ManagedChannel channel = ManagedChannelBuilder.forAddress("localhost", serverPort)
    .intercept(grpcTracing.newClientInterceptor())
    .usePlaintext(true)
    .build();

Sampling and data policy

Please read the RPC documentation before proceeding, as it covers important topics such as which tags are added to spans, and how traces are sampled.

RPC model mapping

As mentioned above, the RPC model types RpcRequest and RpcResponse allow portable sampling decisions and tag parsing.

gRPC maps to this model as follows:

• RpcRequest.service() - text preceding the first slash ('/') in MethodDescriptor.fullMethodName
  • Ex. "helloworld.Greeter" for a full method name "helloworld.Greeter/SayHello"
• RpcRequest.method() - text following the first slash ('/') in MethodDescriptor.fullMethodName
  • Ex. "SayHello" for a full method name "helloworld.Greeter/SayHello"
• RpcResponse.errorCode() - Status.Code.name() when not Status.isOk()
  • Ex. null for Status.Code.OK and UNKNOWN for Status.Code.UNKNOWN

gRPC-specific model

The GrpcRequest and GrpcResponse are available for custom sampling and tag parsing.

Here is an example that adds default tags, and if gRPC, the method type (ex "UNARY"):

Tag<GrpcRequest> methodType = new Tag<GrpcRequest>("grpc.method_type") {
  @Override protected String parseValue(GrpcRequest input, TraceContext context) {
    return input.methodDescriptor().getType().name();
  }
};

RpcRequestParser addMethodType = (req, context, span) -> {
  RpcRequestParser.DEFAULT.parse(req, context, span);
  if (req instanceof GrpcRequest) methodType.tag((GrpcRequest) req, span);
};

grpcTracing = GrpcTracing.create(RpcTracing.newBuilder(tracing)
    .clientRequestParser(addMethodType)
    .serverRequestParser(addMethodType).build());

Development

If you are working on this module, then you need to run mvn install to first compile the protos. Once the protos are compiled, then can be found in the directories:

./target/generated-test-sources/protobuf/grpc-java ./target/generated-test-sources/protobuf/java

You may need to add the above directories as test sources in your IDE.