OpentelemetrySDK的简单用法

Opentelemetry SDK的简单用法

概述

Opentelemetry trace的简单架构图如下，客户端和服务端都需要启动一个traceProvider，主要用于将trace数据传输到registry(如jaeger、opencensus等)。client和server通过context将整个链路串起来。

traceProvider会周期性的将数据推送到Registry，默认是5s

func NewBatchSpanProcessor(exporter SpanExporter, options ...BatchSpanProcessorOption) SpanProcessor {   ...   o := BatchSpanProcessorOptions{      BatchTimeout:       time.Duration(env.BatchSpanProcessorScheduleDelay(DefaultScheduleDelay)) * time.Millisecond,      ExportTimeout:      time.Duration(env.BatchSpanProcessorExportTimeout(DefaultExportTimeout)) * time.Millisecond,      MaxQueueSize:       maxQueueSize,      MaxExportBatchSize: maxExportBatchSize,   }   ...}

下面是官方提供的SDK，它实现了opentelemetry的API，也是操作opentelemetry所使用的基本库：

	tracesdk "go.opentelemetry.io/otel/sdk/trace"

创建TracerProvider

要使用trace，首先要创建一个TracerProvider，定义exporter以及相关属性。

使用全局TracerProvider

参数表示应用名称或代码库名称

var tracer = otel.Tracer("app_or_package_name")

创建TracerProvider

下面展示了使用Jaeger作为exporter的tracerProvider，其中包含两个概念：exporter和resource。前者为发送遥测数据的目的地，如jaeger、zepkin、opencensus等；后者通常用于添加非临时的底层元数据信息，如主机名，实例ID等。

// tracerProvider returns an OpenTelemetry TracerProvider configured to use// the Jaeger exporter that will send spans to the provided url. The returned// TracerProvider will also use a Resource configured with all the information// about the application.func tracerProvider(url string) (*tracesdk.TracerProvider, error) {	// Create the Jaeger exporter	exp, err := jaeger.New(jaeger.WithCollectorEndpoint(jaeger.WithEndpoint(url)))	if err != nil {		return nil, err	}	tp := tracesdk.NewTracerProvider(		// Always be sure to batch in production.		tracesdk.WithBatcher(exp),		// Record information about this application in a Resource.		tracesdk.WithResource(resource.NewWithAttributes(			semconv.SchemaURL,			semconv.ServiceNameKey.String(service),			attribute.String("environment", environment),			attribute.Int64("ID", id),		)),	)	return tp, nil}

可以使用如下方式创建resource，semconv包可以为资源属性提供规范化的名称。

// newResource returns a resource describing this application.func newResource() *resource.Resource {	r, _ := resource.Merge(		resource.Default(),		resource.NewWithAttributes(			semconv.SchemaURL,			semconv.ServiceNameKey.String("fib"),			semconv.ServiceVersionKey.String("v0.1.0"),			attribute.String("environment", "demo"),		),	)	return r}

注册tracerProvider

如果使用自定义的tracerProvider，需要将其注册为全局tracerProvider：

	tp, err := tracerProvider("http://localhost:14268/api/traces")	if err != nil {		log.Fatal(err)	}	// Register our TracerProvider as the global so any imported	// instrumentation in the future will default to using it.	otel.SetTracerProvider(tp)

启动tracerProvider

	tr := tp.Tracer("component-main")	ctx, span := tr.Start(ctx, "foo")	defer span.End()

关闭tracerProvider

当程序退出前，需要关闭tracerProvider，执行数据清理工作：

	ctx, cancel := context.WithCancel(context.Background())	defer cancel()    // Cleanly shutdown and flush telemetry when the application exits.	defer func(ctx context.Context) {		// Do not make the application hang when it is shutdown.		ctx, cancel = context.WithTimeout(ctx, time.Second*5)		defer cancel()		if err := tp.Shutdown(ctx); err != nil {			log.Fatal(err)		}	}(ctx)

span的简单用法

tracer会创建span，为了创建span，需要一个context.Context实例。该context通常来自于请求对象，或已经存在的父span。Go的context用于保存活动的span，当span启用后，就可以操作创建好的span以及其包含的已修改的上下文。当span结束后，其将成为不可变状态。

下面为从请求中获取span：

func httpHandler(w http.ResponseWriter, r *http.Request) {	ctx, span := tracer.Start(r.Context(), "hello-span")	defer span.End()	// do some work to track with hello-span}

获取当前span

// This context needs contain the active span you plan to extract.ctx := context.TODO()span := trace.SpanFromContext(ctx)// Do something with the current span, optionally calling `span.End()` if you want it to en

创建嵌套的span

下面将childSpan嵌套在了parentSpan中，表示串行执行：

func parentFunction(ctx context.Context) {	ctx, parentSpan := tracer.Start(ctx, "parent")	defer parentSpan.End()	// call the child function and start a nested span in there	childFunction(ctx)	// do more work - when this function ends, parentSpan will complete.}func childFunction(ctx context.Context) {	// Create a span to track `childFunction()` - this is a nested span whose parent is `parentSpan`	ctx, childSpan := tracer.Start(ctx, "child")	defer childSpan.End()	// do work here, when this function returns, childSpan will complete.}

设置span相关的信息

添加属性

属性是一组key/value元数据，用于聚合、过滤以及对traces进行分组。

// setting attributes at creation...ctx, span = tracer.Start(ctx, "attributesAtCreation", trace.WithAttributes(attribute.String("hello", "world")))// ... and after creationspan.SetAttributes(attribute.Bool("isTrue", true), attribute.String("stringAttr", "hi!"))

可以使用如下方式预设置属性，然后再添加到span中：

var myKey = attribute.Key("myCoolAttribute")span.SetAttributes(myKey.String("a value"))

注：trace的属性并不是随便定义的，它有一些特定的约束，参见官方约定以及uptrace总结的约束

添加事件

事件为可读的消息，表示在span的生命周期中"发生了某些事情"。例如，假设某个函数需要获取锁来访问互斥的资源时，可以在两个节点创建事件，一个是尝试访问资源时，另一个是获取到锁时。如：

span.AddEvent("Acquiring lock")mutex.Lock()span.AddEvent("Got lock, doing work...")// do stuffspan.AddEvent("Unlocking")mutex.Unlock()

事件的一个有用的特点是，它们的时间戳显示为从span开始的偏移量(即事件发生的真实时间)。

事件也可以配置属性：

span.AddEvent("Cancelled wait due to external signal", trace.WithAttributes(attribute.Int("pid", 4328), attribute.String("signal", "SIGHUP")))

设置span状态

通常用于表示操作是否有异常。默认状态为Unset，可以手动将其设置为Ok，但通常没必要这么做。

result, err := operationThatCouldFail()if err != nil {	span.SetStatus(codes.Error, "operationThatCouldFail failed")}

记录错误

用于记录错误日志或调用栈等信息。强烈建议在使用RecordError的同时，通过SetStatus将span状态设置为Error：

result, err := operationThatCouldFail()if err != nil {	span.SetStatus(codes.Error, "operationThatCouldFail failed")	span.RecordError(err)}

完整代码

下面是对本地的一个函数bar生成trace信息：

func tracerProvider(url string) (*tracesdk.TracerProvider, error) {	// Create the Jaeger exporter	exp, err := jaeger.New(jaeger.WithCollectorEndpoint(jaeger.WithEndpoint(url)))	if err != nil {		return nil, err	}	tp := tracesdk.NewTracerProvider(		// Always be sure to batch in production.		tracesdk.WithBatcher(exp),		// Record information about this application in a Resource.		tracesdk.WithResource(resource.NewWithAttributes(			semconv.SchemaURL,			semconv.ServiceNameKey.String(service),			attribute.String("environment", environment),			attribute.Int64("ID", id),		)),	)	return tp, nil}func main() {	tp, err := tracerProvider("http://localhost:14268/api/traces")	if err != nil {		log.Fatal(err)	}	// Register our TracerProvider as the global so any imported	// instrumentation in the future will default to using it.	otel.SetTracerProvider(tp)	ctx, cancel := context.WithCancel(context.Background())	defer cancel()	// Cleanly shutdown and flush telemetry when the application exits.	defer func(ctx context.Context) {		// Do not make the application hang when it is shutdown.		ctx, cancel = context.WithTimeout(ctx, time.Second*5)		defer cancel()		if err := tp.Shutdown(ctx); err != nil {			log.Fatal(err)		}	}(ctx)	tr := tp.Tracer("component-main")	ctx, span := tr.Start(ctx, "foo")	defer span.End()	bar(ctx)}func bar(ctx context.Context) {	// Use the global TracerProvider.	tr := otel.Tracer("component-bar")	_, span := tr.Start(ctx, "bar")	span.SetAttributes(attribute.Key("testset").String("value"))	defer span.End()	// Do bar...}

Trace context的跨服务传播

为了跨服务传播Trace context需要注册一个propagator ，通常在创建注册TracerProvider之后执行。

func initTracer() (*sdktrace.TracerProvider, error) {	// Create stdout exporter to be able to retrieve	// the collected spans.	exporter, err := stdout.New(stdout.WithPrettyPrint())	if err != nil {		return nil, err	}	// For the demonstration, use sdktrace.AlwaysSample sampler to sample all traces.	// In a production application, use sdktrace.ProbabilitySampler with a desired probability.	tp := sdktrace.NewTracerProvider(		sdktrace.WithSampler(sdktrace.AlwaysSample()),		sdktrace.WithBatcher(exporter),	)	otel.SetTracerProvider(tp)	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{}))	return tp, err}

如上注册了两种propagator ：TraceContext和Baggage，因此可以使用这两种数据结构传播上下文。

TraceContext

下面是gorilla/mux的服务端代码，通过 trace.SpanFromContext(r.Context())从请求的context构建span，当然也可以通过tracer.Start(c.Context(), "getUser", oteltrace.WithAttributes(attribute.String("id", id)))这种方式启动一个新的span：

func TestPropagationWithCustomPropagators(t *testing.T) {	prop := propagation.TraceContext{}	r := httptest.NewRequest("GET", "/user/123", nil)	w := httptest.NewRecorder()	ctx := trace.ContextWithRemoteSpanContext(context.Background(), sc)	prop.Inject(ctx, propagation.HeaderCarrier(r.Header))	var called bool	router := mux.NewRouter()	router.Use(Middleware("foobar", WithPropagators(prop)))	router.HandleFunc("/user/{id}", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {		called = true		span := trace.SpanFromContext(r.Context())        defer span.End()		assert.Equal(t, sc, span.SpanContext())		w.WriteHeader(http.StatusOK)	}))	router.ServeHTTP(w, r)	assert.True(t, called, "failed to run test")}

baggage

下面是使用baggage的客户端和服务端代码，需要注意的是，客户端需要使用otelhttp。

客户端代码：

package mainimport (	"context"	"flag"	"fmt"	"io/ioutil"	"log"	"net/http"	"time"	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"	"go.opentelemetry.io/otel"	"go.opentelemetry.io/otel/baggage"	stdout "go.opentelemetry.io/otel/exporters/stdout/stdouttrace"	"go.opentelemetry.io/otel/propagation"	sdktrace "go.opentelemetry.io/otel/sdk/trace"	semconv "go.opentelemetry.io/otel/semconv/v1.10.0"	"go.opentelemetry.io/otel/trace")func initTracer() (*sdktrace.TracerProvider, error) {	// Create stdout exporter to be able to retrieve	// the collected spans.	exporter, err := stdout.New(stdout.WithPrettyPrint())	if err != nil {		return nil, err	}	// For the demonstration, use sdktrace.AlwaysSample sampler to sample all traces.	// In a production application, use sdktrace.ProbabilitySampler with a desired probability.	tp := sdktrace.NewTracerProvider(		sdktrace.WithSampler(sdktrace.AlwaysSample()),		sdktrace.WithBatcher(exporter),	)	otel.SetTracerProvider(tp)	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{}))	return tp, err}func main() {	tp, err := initTracer()	if err != nil {		log.Fatal(err)	}	defer func() {		if err := tp.Shutdown(context.Background()); err != nil {			log.Printf("Error shutting down tracer provider: %v", err)		}	}()	url := flag.String("server", "http://localhost:7777/hello", "server url")	flag.Parse()	client := http.Client{Transport: otelhttp.NewTransport(http.DefaultTransport)}	bag, _ := baggage.Parse("username=donuts")	ctx := baggage.ContextWithBaggage(context.Background(), bag)	var body []byte	tr := otel.Tracer("example/client")	err = func(ctx context.Context) error {		ctx, span := tr.Start(ctx, "say hello", trace.WithAttributes(semconv.PeerServiceKey.String("ExampleService")))		defer span.End()		req, _ := http.NewRequestWithContext(ctx, "GET", *url, nil)		fmt.Printf("Sending request...\n")		res, err := client.Do(req)		if err != nil {			panic(err)		}		body, err = ioutil.ReadAll(res.Body)		_ = res.Body.Close()		return err	}(ctx)	if err != nil {		log.Fatal(err)	}	fmt.Printf("Response Received: %s\n\n\n", body)	fmt.Printf("Waiting for few seconds to export spans ...\n\n")	time.Sleep(10 * time.Second)	fmt.Printf("Inspect traces on stdout\n")}

服务端代码：

package mainimport (	"context"	"io"	"log"	"net/http"	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"	"go.opentelemetry.io/otel"	"go.opentelemetry.io/otel/attribute"	"go.opentelemetry.io/otel/baggage"	stdout "go.opentelemetry.io/otel/exporters/stdout/stdouttrace"	"go.opentelemetry.io/otel/propagation"	"go.opentelemetry.io/otel/sdk/resource"	sdktrace "go.opentelemetry.io/otel/sdk/trace"	semconv "go.opentelemetry.io/otel/semconv/v1.10.0"	"go.opentelemetry.io/otel/trace")func initTracer() (*sdktrace.TracerProvider, error) {	// Create stdout exporter to be able to retrieve	// the collected spans.	exporter, err := stdout.New(stdout.WithPrettyPrint())	if err != nil {		return nil, err	}	// For the demonstration, use sdktrace.AlwaysSample sampler to sample all traces.	// In a production application, use sdktrace.ProbabilitySampler with a desired probability.	tp := sdktrace.NewTracerProvider(		sdktrace.WithSampler(sdktrace.AlwaysSample()),		sdktrace.WithBatcher(exporter),		sdktrace.WithResource(resource.NewWithAttributes(semconv.SchemaURL, semconv.ServiceNameKey.String("ExampleService"))),	)	otel.SetTracerProvider(tp)	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{}))	return tp, err}func main() {	tp, err := initTracer()	if err != nil {		log.Fatal(err)	}	defer func() {		if err := tp.Shutdown(context.Background()); err != nil {			log.Printf("Error shutting down tracer provider: %v", err)		}	}()	uk := attribute.Key("username")	helloHandler := func(w http.ResponseWriter, req *http.Request) {		ctx := req.Context()		span := trace.SpanFromContext(ctx) // span为Hello        defer span.End()		bag := baggage.FromContext(ctx)		span.AddEvent("handling this...", trace.WithAttributes(uk.String(bag.Member("username").Value())))		_, _ = io.WriteString(w, "Hello, world!\n")	}    // otelhttp.NewHandler会在处理请求的同时创建一个名为Hello的span	otelHandler := otelhttp.NewHandler(http.HandlerFunc(helloHandler), "Hello")	http.Handle("/hello", otelHandler)	err = http.ListenAndServe(":7777", nil)	if err != nil {		log.Fatal(err)	}}

上述代码生成的链路跟踪如下，client的HTTP GET会调用server端的Hello。Server的Hello span是在处理请求时生成的，上述用的是otelhttp，其他registry也是类似的处理方式。

使用如下代码则可以启动两个独立的span，可以表示两个并行的任务：

	helloHandler := func(w http.ResponseWriter, req *http.Request) {		ctx := req.Context()		ctx, span1 := tracer.Start(ctx, "span1 proecss", trace.WithLinks())		defer span1.End()		bag := baggage.FromContext(req.Context())		span1.SetAttributes(attribute.String("span1", "test1"))		span1.AddEvent("span1 handling this...", trace.WithAttributes(uk.String(bag.Member("username").Value())))		ctx, span2 := tracer.Start(req.Context(), "span2 proecss", trace.WithLinks())		defer span2.End()		span2.SetAttributes(attribute.String("span2", "test2"))		span2.AddEvent("span2 handling this...", trace.WithAttributes(uk.String(bag.Member("username").Value())))		_, _ = io.WriteString(w, "Hello, world!\n")	}

此外还可以通过baggage.NewKeyValueProperty("key", "value")等方式创建baggage。

注：baggage要遵循W3C Baggage 规范。

支持otel的工具

官方给出了很多Registry，如Gorilla Mux、GORM、Gin-gonic 、gRPC等。更多可以参见官方代码库。

采样

provider := sdktrace.NewTracerProvider(	sdktrace.WithSampler(sdktrace.AlwaysSample()),)

• AlwaysSample：采集每条链路信息
• NeverSample ：不采集
• TraceIDRatioBased：按比例采集，即如果将其设置.5，则表示采集一半链路信息
• ParentBased：根据传入的采样决策表现不同。通常会父span已采样的span进行采样，而不会对父span未采样的span进行采样。

生产中可以考虑使用TraceIDRatioBased和ParentBased。

参考

• Opentelemetry 官方指导