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Setting up open telemetry for golang on google cloud platform

Alex Mammay
・2 min read

If you are looking to start capturing deeper insights around the work your application is performing, open telemetry is the way to go for capturing data points while using a consistent api surface.

Here is a quick snippet for how you can setup app engine/cloud run/cloud functions/GKE with open telemetry in GCP. This will leverage using the X-Cloud-Trace-Context header that comes in from every request from the GFE.

Source code for the propagationgcp pacakge can be found here

https://github.com/amammay/propagationgcp

package main

import (
    "cloud.google.com/go/compute/metadata"
    "context"
    "fmt"
    texporter "github.com/GoogleCloudPlatform/opentelemetry-operations-go/exporter/trace"
    "github.com/amammay/propagationgcp" // ablility to parse X-Cloud-Trace-Context
    "go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
    "go.opentelemetry.io/otel"
    "go.opentelemetry.io/otel/exporters/stdout"
    "go.opentelemetry.io/otel/propagation"
    sdktrace "go.opentelemetry.io/otel/sdk/trace"
    "go.opentelemetry.io/otel/trace"

    "log"
    "net/http"
    "os"
    "time"
)

func main() {
    if err := run(); err != nil {
        fmt.Fprintf(os.Stderr, "run(): %v", err)
        os.Exit(1)
    }
}

func run() error {
    projectID := ""
    onGCE := metadata.OnGCE()
    if onGCE {
        // infer our project id from the metadata server
        id, err := metadata.ProjectID()
        if err != nil {
            return fmt.Errorf("metadata.ProjectID(): %v", err)
        }
        projectID = id
    }
    // init open telem, while allowing us to defer the teardown and flushing of our exporter
    tracerShutdown, err := initTracer(context.Background(), projectID, onGCE)
    if err != nil {
        return fmt.Errorf("initTracer(): %v", err)
    }
    defer tracerShutdown()

    mux := http.NewServeMux()
    mux.HandleFunc("/", func(writer http.ResponseWriter, request *http.Request) {
        ctx := request.Context()
        //create our custom span of work
        ctx, span := trace.SpanFromContext(ctx).Tracer().Start(ctx, "hello-world")
        defer span.End()
        writer.Write([]byte("hello world"))
    })

    // add http middleware for tracing
    otelWrapper := otelhttp.NewHandler(mux, "requesthandler")

    port := os.Getenv("PORT")
    if port == "" {
        port = "8080"
    }
    httpServer := http.Server{
        Addr:         ":" + port,
        Handler:      otelWrapper,
        ReadTimeout:  45 * time.Second,
        WriteTimeout: 45 * time.Second,
    }
    log.Printf("starting server on %q", httpServer.Addr)
    return httpServer.ListenAndServe()
}

func initTracer(ctx context.Context, projectID string, onGCE bool) (func(), error) {
    var tpos []sdktrace.TracerProviderOption
    // if our code is running on GCP (cloud run/functions/app engine/gke) then we will export directly to cloud tracing
    if onGCE {
        exporter, err := texporter.NewExporter(texporter.WithProjectID(projectID))
        if err != nil {
            return nil, fmt.Errorf("texporter.NewExporter(): %v", err)
        }
        tpos = append(tpos, sdktrace.WithBatcher(exporter))
    } else {
        exporter, err := stdout.NewExporter(stdout.WithPrettyPrint())
        if err != nil {
            return nil, fmt.Errorf("stdout.NewExporter(): %v", err)
        }
        tpos = append(tpos, sdktrace.WithBatcher(exporter))
    }

    tp := sdktrace.NewTracerProvider(tpos...)

    otel.SetTracerProvider(tp)

    propagator := propagation.NewCompositeTextMapPropagator(
        propagation.TraceContext{},
        propagation.Baggage{},
        propagationgcp.HTTPFormat{}, //adding this propagator allows for extracting X-Cloud-Trace-Context
    )
    otel.SetTextMapPropagator(propagator)

    return func() {
        err := tp.ForceFlush(ctx)
        if err != nil {
            log.Printf("tracerProvider.ForceFlush(): %v", err)
        }
    }, nil
}
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