带有Google App Engine Go 1.11运行时的Stackdriver Trace

I would like to get Stackdriver Trace to work on the new Go 1.11 standard runtime on Google App Engine. This is all still labeled as beta so maybe it just doesn't quite work yet. However, I followed the step-by-step directions and it isn't working. I deployed the code (almost) exactly as it is listed in the link and my traces are flat (i.e. doesn't include the waterfall view I would expect with the incoming request at the top and the outgoing request nested underneath).

Sample code

package main

import (
    "fmt"
    "log"
    "net/http"
    "os"

    "contrib.go.opencensus.io/exporter/stackdriver"
    "contrib.go.opencensus.io/exporter/stackdriver/propagation"
    "go.opencensus.io/plugin/ochttp"
    "go.opencensus.io/trace"
)

func main() {
    // Create and register a OpenCensus Stackdriver Trace exporter.
    exporter, err := stackdriver.NewExporter(stackdriver.Options{
        ProjectID: os.Getenv("GOOGLE_CLOUD_PROJECT"),
    })
    if err != nil {
        log.Fatal(err)
    }
    trace.RegisterExporter(exporter)

    client := &http.Client{
        Transport: &ochttp.Transport{
            // Use Google Cloud propagation format.
            Propagation: &propagation.HTTPFormat{},
        },
    }

    handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        req, _ := http.NewRequest("GET", "https://www.google.com/robots.txt", nil)

        // The trace ID from the incoming request will be
        // propagated to the outgoing request.
        req = req.WithContext(r.Context())

        // The outgoing request will be traced with r's trace ID.
        resp, err := client.Do(req)
        if err != nil {
            log.Fatal(err)
        }
        defer resp.Body.Close()

        fmt.Fprint(w, "OK")
    })
    http.Handle("/foo", handler)
    log.Fatal(http.ListenAndServe(":"+os.Getenv("PORT"), &ochttp.Handler{}))
}

Sample trace:

As written in the reply comment in the original question, can you try the config for sampling?: trace.AlwaysSample()

You can find some comments about sampling rate in OpenCensus Trace documentation and godoc of OpenCensus Trace library:

By default, traces will be sampled relatively rarely. To change the sampling frequency for your entire program, call ApplyConfig. Use a ProbabilitySampler to sample a subset of traces, or use AlwaysSample to collect a trace on every run: