Using opentracing to track HTTP request latency in go

Jiedao jdon 2021-05-03 08:36:08
using opentracing track http request

stay Go 1.7, We have a new bag / HTTP / httptrace Provides a convenient mechanism , Look at one HTTP What happens when you ask . In this paper , It will show how it can be used in the case of distributed tracking , By using OpenTracing API Tracking a client and a server , And the visual results are shown in Zipkin UI .

What is distributed tracking and OpenTracing?

Distributed tracking is to monitor and analyze microservice architecture system , Export the result to X-TRACE, Like Google's Dapper and Twitter Of Zipkin . Their underlying principle is distributed environment propagation , Some of the metadata involved is associated with every request to enter the system , And it propagates metadata across threads and process boundaries to follow requests in and out of various microservice calls . If we assign each inbound request a unique ID And make it part of the distributed context , Then we can combine various performance analysis data from multiple threads and processes into a unified representation of the execution requests of our system “ track ” in .

Distributed tracking needs to use Hook Hook and context propagation mechanism to test application code ( Or the framework it uses ). When we're in Uber When we started building our distributed tracking system , We soon realized that , There is no good API Provide developers with internal consistency between programming languages , Then it cannot be bound to the specified tracking system . original , It's not just that we have this kind of thinking ,2015 year 10 A new community was formed in June , It gave birth OpenTracing API, An open , Manufacturer neutral , Language independent distributed tracking standards . You can read more about Ben Sigelman of OpenTracing The article behind motivation and design principles .

Let's look at the code :

import (
// We will talk about this later
var tracer opentracing.Tracer
func AskGoogle(ctx context.Context) error {
// retrieve current Span from Context
var parentCtx opentracing.SpanContext
parentSpan := opentracing.SpanFromContext(ctx);
if parentSpan != nil {
parentCtx = parentSpan.Context()
// start a new Span to wrap HTTP request
span := tracer.StartSpan(
"ask google",
// make sure the Span is finished once we're done
defer span.Finish()
// make the Span current in the context
ctx = opentracing.ContextWithSpan(ctx, span)
// now prepare the request
req, err := http.NewRequest("GET", "", nil)
if err != nil {
return err
// attach ClientTrace to the Context, and Context to request 
trace := NewClientTrace(span)
ctx = httptrace.WithClientTrace(ctx, trace)
req = req.WithContext(ctx)
// execute the request
res, err := http.DefaultClient.Do(req)
if err != nil {
return err
// Google home page is not too exciting, so ignore the result
return nil

Here are some points to pay attention to :

1. I dodged tracer Variable initialization .

2.AskGoogle Function acceptance context.Context object . This is for developing distributed applications Go Recommend ways , Because context objects are meant to spread in a distributed environment .

3. Let's assume that the context already contains the parent trace Span. OpenTracing API Medium Span Is used to represent the unit of work performed by a microservice .HTTP Call can be wrapped in tracking Span Operation cases in . When we run a service that processes inbound requests , The service usually creates a trace scope for each request , And store it in context , To be available when making a downstream call to another service ( In our example, for ).

4. We start a new sub Span To package out of the station HTTP call . If the father Span defect , It's a good way .

5. Last , Making HTTP Request before , Let's instantiate a ClientTrace And attach it to the request .

ClientTrace Structure is httptrace The basic building blocks of . It allows us to HTTP Registration during the lifetime of the request will be performed by HTTP Callback function executed by client . for example ,ClientTrace There's a way to structure :

type ClientTrace struct {
// DNSStart is called when a DNS lookup begins.
DNSStart func(DNSStartInfo)
// DNSDone is called when a DNS lookup ends.
DNSDone func(DNSDoneInfo)

We are NewClientTrace Method to create an instance of this structure :

func NewClientTrace(span opentracing.Span) *httptrace.ClientTrace {
trace := &clientTrace{span: span}
return &httptrace.ClientTrace {
DNSStart: trace.dnsStart,
DNSDone: trace.dnsDone,
// clientTrace holds a reference to the Span and
// provides methods used as ClientTrace callbacks
type clientTrace struct {
span opentracing.Span
func (h *clientTrace) dnsStart(info httptrace.DNSStartInfo) {
log.String("event", "DNS start"),
log.Object("host", info.Host),
func (h *clientTrace) dnsDone(httptrace.DNSDoneInfo) {
h.span.LogKV(log.String("event", "DNS done"))

We are DBBStart and DNSDone Event implementation registers two callback functions , Through private structures clientTrace Keep a point tracking Span. In the callback method , We use Span Key value record of API To record information about events , as well as Span Itself implies a captured timestamp .

You're not talking about UI Is it ?

OpenTracing API The way we work is , Once trace is called Span Of Finish() Method ,Span The captured data will be sent to the back end of the tracking system , Usually sent asynchronously in the background . then , We can use the tracking system UI To find the trace and visualize it on the timeline . However , The above examples are just to illustrate the use of OpenTracing And httptrace Principle . For a real working example , We will use the existing library . Using this library, our client code doesn't have to worry about tracking the actual HTTP call . however , We still want to create a top-level tracking Span To represent the overall execution of the client application , And record any errors .

package main
import (
otlog ""
func runClient(tracer opentracing.Tracer) {
// nethttp.Transport from go-stdlib will do the tracing
c := &http.Client{Transport: &nethttp.Transport{}}
// create a top-level span to represent full work of the client
span := tracer.StartSpan(client)
span.SetTag(string(ext.Component), client)
defer span.Finish()
ctx := opentracing.ContextWithSpan(context.Background(), span)
req, err := http.NewRequest(
fmt.Sprintf("http://localhost:%s/", *serverPort),
if err != nil {
onError(span, err)
req = req.WithContext(ctx)
// wrap the request in nethttp.TraceRequest
req, ht := nethttp.TraceRequest(tracer, req)
defer ht.Finish()
res, err := c.Do(req)
if err != nil {
onError(span, err)
defer res.Body.Close()
body, err := ioutil.ReadAll(res.Body)
if err != nil {
onError(span, err)
fmt.Printf("Received result: %s\n", string(body))
func onError(span opentracing.Span, err error) {
// handle errors by recording them in the span
span.SetTag(string(ext.Error), true)

The client code above calls the local server . Let's make it happen .

package main
import (
func getTime(w http.ResponseWriter, r *http.Request) {
log.Print("Received getTime request")
t := time.Now()
ts := t.Format("Mon Jan _2 15:04:05 2006")
io.WriteString(w, fmt.Sprintf("The time is %s", ts))
func redirect(w http.ResponseWriter, r *http.Request) {
http.Redirect(w, r,
fmt.Sprintf("http://localhost:%s/gettime", *serverPort), 301)
func runServer(tracer opentracing.Tracer) {
http.HandleFunc("/gettime", getTime)
http.HandleFunc("/", redirect)
log.Printf("Starting server on port %s", *serverPort)
fmt.Sprintf(":%s", *serverPort),
// use nethttp.Middleware to enable OpenTracing for server
nethttp.Middleware(tracer, http.DefaultServeMux))

Be careful , Client to root endpoint “/” Request , But the server redirects it to “/ gettime” Endpoint . This allows us to better illustrate how to capture traces in the tracking system .

Tracing HTTP request latency in Go with OpenTracin

[ The quilt banq On 2016-11-25 09:00 A modified ]

本文为[Jiedao jdon]所创,转载请带上原文链接,感谢

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