Opentelemetry SDK的簡單用法

Opentelemetry SDK的簡單用法

概述

Opentelemetry trace的簡單架構圖如下，使用者端和伺服器端都需要啟動一個traceProvider，主要用於將trace資料傳輸到registry(如jaeger、opencensus等)。client和server通過context將整個鏈路串起來。

traceProvider會週期性的將資料推播到Registry，預設是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，它實現了opentelemetry的API，也是操作opentelemetry所使用的基本庫：

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

建立TracerProvider

要使用trace，首先要建立一個TracerProvider，定義exporter以及相關屬性。

使用全域性TracerProvider

參數列示應用名稱或程式碼庫名稱

var tracer = otel.Tracer("app_or_package_name")

建立TracerProvider

下面展示了使用Jaeger作為exporter的tracerProvider，其中包含兩個概念：exporter和resource。前者為傳送遙測資料的目的地，如jaeger、zepkin、opencensus等；後者通常用於新增非臨時的底層後設資料資訊，如主機名，範例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
}

可以使用如下方式建立resource，semconv包可以為資源屬性提供規範化的名稱。

// 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
}

註冊tracerProvider

如果使用自定義的tracerProvider，需要將其註冊為全域性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)

啟動tracerProvider

	tr := tp.Tracer("component-main")

	ctx, span := tr.Start(ctx, "foo")
	defer span.End()

關閉tracerProvider

當程式退出前，需要關閉tracerProvider，執行資料清理工作：

	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的簡單用法

tracer會建立span，為了建立span，需要一個context.Context範例。該context通常來自於請求物件，或已經存在的父span。Go的context用於儲存活動的span，當span啟用後，就可以操作建立好的span以及其包含的已修改的上下文。當span結束後，其將成為不可變狀態。

下面為從請求中獲取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
}

獲取當前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

建立巢狀的span

下面將childSpan巢狀在了parentSpan中，表示序列執行：

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.
}

設定span相關的資訊

新增屬性

屬性是一組key/value後設資料，用於聚合、過濾以及對traces進行分組。

// 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!"))

可以使用如下方式預設定屬性，然後再新增到span中：

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

注：trace的屬性並不是隨便定義的，它有一些特定的約束，參見官方約定以及uptrace總結的約束

新增事件

事件為可讀的訊息，表示在span的生命週期中"發生了某些事情"。例如，假設某個函數需要獲取鎖來存取互斥的資源時，可以在兩個節點建立事件，一個是嘗試存取資源時，另一個是獲取到鎖時。如：

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

事件的一個有用的特點是，它們的時間戳顯示為從span開始的偏移量(即事件發生的真實時間)。

事件也可以設定屬性：

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

設定span狀態

通常用於表示操作是否有異常。預設狀態為Unset，可以手動將其設定為Ok，但通常沒必要這麼做。

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

記錄錯誤

用於記錄錯誤紀錄檔或呼叫棧等資訊。強烈建議在使用RecordError的同時，通過SetStatus將span狀態設定為Error：

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

完整程式碼

下面是對原生的一個函數bar生成trace資訊：

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的跨服務傳播

為了跨服務傳播Trace context需要註冊一個propagator ，通常在建立註冊TracerProvider之後執行。

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
}

如上註冊了兩種propagator ：TraceContext和Baggage，因此可以使用這兩種資料結構傳播上下文。

TraceContext

下面是gorilla/mux的伺服器端程式碼，通過 trace.SpanFromContext(r.Context())從請求的context構建span，當然也可以通過tracer.Start(c.Context(), "getUser", oteltrace.WithAttributes(attribute.String("id", id)))這種方式啟動一個新的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的使用者端和伺服器端程式碼，需要注意的是，使用者端需要使用otelhttp。

使用者端程式碼：

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: %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")
}

伺服器端程式碼：

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為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會在處理請求的同時建立一個名為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)
	}
}

上述程式碼生成的鏈路跟蹤如下，client的HTTP GET會呼叫server端的Hello。Server的Hello span是在處理請求時生成的，上述用的是otelhttp，其他registry也是類似的處理方式。

使用如下程式碼則可以啟動兩個獨立的span，可以表示兩個並行的任務：

	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")
	}

此外還可以通過baggage.NewKeyValueProperty("key", "value")等方式建立baggage。

注：baggage要遵循W3C Baggage 規範。

支援otel的工具

官方給出了很多Registry，如Gorilla Mux、GORM、Gin-gonic 、gRPC等。更多可以參見官方程式碼庫。

取樣

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

• AlwaysSample：採集每條鏈路資訊
• NeverSample ：不採集
• TraceIDRatioBased：按比例採集，即如果將其設定.5，則表示採集一半鏈路資訊
• ParentBased：根據傳入的取樣決策表現不同。通常會父span已取樣的span進行取樣，而不會對父span未取樣的span進行取樣。

生產中可以考慮使用TraceIDRatioBased和ParentBased。

參考

• Opentelemetry 官方指導