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 creation span.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 stuff span.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 main import ( "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: %snnn", body) fmt.Printf("Waiting for few seconds to export spans ...nn") time.Sleep(10 * time.Second) fmt.Printf("Inspect traces on stdoutn") } 服务端代码：
package main import ( "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。
