Built-in instrumentation modules does not mention asynchronous tracing using apm-agent-go.

[shubhamsharma7867]

Hey,
I noticed that the documentation https://www.elastic.co/guide/en/apm/guide/8.11/apm-distributed-tracing.html - highlights distributed tracing but no information on asynchronous tracing is covered. By asynchronous tracing, I mean; when spinning a routine with a context opposed to the context received from the server, and priority is given to the latter (server's context) there is a possibility of the overall context being cancelled before another service call from that spun routine. This process is carried out using built-in instrumentation module, apm-grpc.

Below is the server side code which is being called by a grpc simple client having a interceptor apmgrpc.NewUnaryClientInterceptor()
and ideally it show me a span

`
type Server struct {
pb.AddServiceServer
clientConn pb.AddServiceClient
}

func main() {
lis, err := net.Listen("tcp", addr)
if err != nil {
log.Fatal(lis)
}
log.Print("listening at port", addr)
cc, err := grpc.Dial("localhost:8080", grpc.WithTransportCredentials(insecure.NewCredentials()), grpc.WithUnaryInterceptor(apmgrpc.NewUnaryClientInterceptor()))
if err != nil {
panic(err)
}
client := pb.NewAddServiceClient(cc)
server := Server{
clientConn: client,
}

s := grpc.NewServer(grpc.UnaryInterceptor(apmgrpc.NewUnaryServerInterceptor()))
pb.RegisterAddServiceServer(s, &server)

if s.Serve(lis); err != nil {
	log.Fatal("problem in starting the server", lis)
}

}

func (s *Server) Add(ctx context.Context, in *pb.NumbersRequest) (*pb.NumberResponse, error) {
var tx *apm.Transaction
if md, ok := metadata.FromIncomingContext(ctx); ok {
tx = apm.TransactionFromContext(ctx)
for _, header := range []string{"elastic-apm-traceparent", "traceparent", "tracestate"} {
if values := md.Get(header); len(values) > 0 {
fmt.Println("inside for")
tx.Context.SetCustom(header, strings.Join(values, " "))
}
}
}
span, ctx := apm.StartSpan(ctx, "server_span", "type")
if tracestate := span.TraceContext().State.String(); tracestate != "" {
span.Name = tracestate
}
var res *pb.NumberResponse
time.Sleep(time.Millisecond * 50)
go func() {
res, _ = s.clientConn.Add(context.Background(), &pb.NumbersRequest{Num_1: 1, Num_2: 2})
fmt.Printf("res: %v\n", res)
}()
return &pb.NumberResponse{
Result: 9,
}, nil
}
`

[axw]

This kind of pattern should ideally be covered by #385.

There is a function for propagating trace context without the cancellation/deadline, which may be useful here: https://pkg.go.dev/go.elastic.co/apm/v2#DetachedContext

[axw]

Closing since we have the other docs issue. Please comment if I misunderstood something.

[shubhamsharma7867]

Hey! I got it. using the apm package functions

`
type Server struct {
pb.AddServiceServer
clientConn1 pb.AddServiceClient
}

func main() {
lis, err := net.Listen("tcp", addr)
if err != nil {
log.Fatal(lis)
}
log.Print("listening at port", addr)
cc, err := grpc.Dial("localhost:8080", grpc.WithTransportCredentials(insecure.NewCredentials()), grpc.WithUnaryInterceptor(apmgrpc.NewUnaryClientInterceptor()))
if err != nil {
panic(err)
}
// creating the client to call the different server
client := pb.NewAddServiceClient(cc)
server := Server{
clientConn1: client,
}
s := grpc.NewServer(grpc.UnaryInterceptor(apmgrpc.NewUnaryServerInterceptor()))
pb.RegisterAddServiceServer(s, &server)

if s.Serve(lis); err != nil {
	log.Fatal("problem in starting the server", lis)
}

}

func (s *Server) Add(ctx context.Context, in *pb.NumbersRequest) (*pb.NumberResponse, error) {
trx := apm.TransactionFromContext(ctx)
if trx == nil {
fmt.Print("it is not nil")
}
//checking for the header in the metadata
var tx *apm.Transaction
if md, ok := metadata.FromIncomingContext(ctx); ok {
tx = apm.TransactionFromContext(ctx)
for _, header := range []string{"elastic-apm-traceparent", "traceparent", "tracestate"} {
if values := md.Get(header); len(values) > 0 {
fmt.Println("inside for")
tx.Context.SetCustom(header, strings.Join(values, " "))
}
}
}

span, ctx := apm.StartSpan(ctx, "server_span", "type")
if tracestate := span.TraceContext().State.String(); tracestate != "" {
	span.Name = tracestate
}
// Spawning the new go-routine with value of the old context
go func() {
	span := apm.SpanFromContext(ctx)
	fmt.Printf("span: %+v\n", span)
	ctx = apm.ContextWithSpan(context.Background(), span)
	ctx := apm.ContextWithTransaction(context.Background(), trx)
	s.clientConn1.Add(ctx, &pb.NumbersRequest{Num_1: 1, Num_2: 2})

}()
return &pb.NumberResponse{
	Result: 9,
}, nil

}
`