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
}
span.End()用于控制一个span是否结束，并加上时间戳
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。
span的事件和属性并不会跨服务传播
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)))这种方式来启动一个新的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: %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 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。
如果服务端不需要解析客户端传递的baggage，且不需要传递context的话，则无需在handler中对span做任何处理，仅在handler外面使用如下方法即可：
otelHandler := otelhttp.NewHandler(http.HandlerFunc(helloHandler), "Hello")
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。如果已经对本span的父span进行了采样，则也会对本span进行采样，反之则不会采样。使用方式如
sdktrace.ParentBased(sdktrace.AlwaysSample())。如果本span是root span，则也会进行采样。
生产中可以考虑使用TraceIDRatioBased和ParentBased。
Tips
- 设置自定义属性时，注意属性字段需要小写