Pre-application latency with AppEngine

[Prateek Malhotra]

I've tested this on both Go 1.12 and Go 1.13: I added tracing to my application and noticed a lag between when AppEngine reports receiving the request and when my application registers receiving the request. In order to eliminate any of my middlewares/setup process as the culprit, I made a barebones handler to test the latency (code found below) and notice anywhere between a ~30-90ms lag time from when AppEngine starts the trace until my application registers the request. This is after I let it "warm" up first with 10 requests.

in Go 1.12:

Browser TTFB: 112.69ms

StackDriver Trace Output:

@0 ms (HTTP load balancer )

Traced time 62.974 ms

Untraced time 46.026 ms

@18.913 ms (AppEngine Entry)

Traced time 0.073 ms

Untraced time 62.901 ms

@50.164 ms (My Application)

in Go 1.13:

Browser TTFB: 62.19ms

StackDriver Trace Output:

@0 ms (HTTP load balancer )

Traced time 21.039 ms

Untraced time 41.961 ms

@18.053 ms (AppEngine Entry)

Traced time 0.066 ms

Untraced time 20.973 ms

@38.181 ms (My Application)

This feels higher than it should but I was curious if this is expected?

app.yaml:

runtime: go112 # or go113

service: latency

go.mod:

module main

go 1.12

require (

contrib.go.opencensus.io/exporter/stackdriver v0.12.8

go.opencensus.io v0.22.2

)

main.go:

package main

import (

"context"

"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() {

ctx := context.Background()

exp, err := stackdriver.NewExporter(stackdriver.Options{

Context:   ctx,

ProjectID: os.Getenv("GOOGLE_CLOUD_PROJECT"),

})

if err != nil {

panic(err)

}

trace.RegisterExporter(exp)

http.HandleFunc("/", indexHandler)

h := TraceHandler(http.DefaultServeMux)

port := os.Getenv("PORT")

if port == "" {

port = "8080"

log.Printf("Defaulting to port %s", port)

}

log.Printf("Listening on port %s", port)

if err := http.ListenAndServe(":"+port, h); err != nil {

log.Fatal(err)

}

}

// TraceHandler sets up OpenCensus middleware for tracing and stats

func TraceHandler(h http.Handler) http.Handler {

return &ochttp.Handler{

Handler:          h,

Propagation:      &propagation.HTTPFormat{},

IsPublicEndpoint: false,

}

}

func indexHandler(w http.ResponseWriter, r *http.Request) {

if r.URL.Path != "/" {

http.NotFound(w, r)

return

}

fmt.Fprint(w, "Hello, World!")

}

Thank you,

Prateek