Opentelemetry是怎么做链路追踪的

Dec 12, 2021 in UNDEFINED
可观测性
2 min read

Table of Content

云原生可观测技术是云原生下很火的一个命题，opentelemetry的定位是统一metrics,trace和log的协议、api、sdk和exporter，他越来越成为云原生技术体系下的可观测性标准。这个博客就是来探究下opentelemetry是什么，做什么，怎么做的。

OpenTelemetry is a collection of tools, APIs, and SDKs. Use it to instrument, generate, collect, and export telemetry data (metrics, logs, and traces) to help you analyze your software’s performance and behavior.

上面是opentelemetry官网对自己的定位。抽取一下关键词，opentelemetry仅提供了api和SDK，不负责后端实现（后端由prometheus、jaeger等实现），用这些api和SDK，你可以做性能数据埋点，生成、收集和导出（generate, collect, and export）监控数据。对这段话最终的理解是opentelemetry只做SDK层面的事，职责的边缘是export数据即止。

概念性的东西不多讲，可以自己到opentelemetry的官网看。我个人的感受是，如果对trace比较了解，完全不用看官网一大堆的Concepts或者specification，他只是定义了一堆convention，也就是标准和协议的部分。对trace比较了解的话，就直接看代码吧。下面的行文采用自下而上的方式，也就是先看看怎么用上opentelemtry（建立信心：opentelemetry就这），然后在看设计层面的东西（深入了解，变成专家）。

使用demo

pom依赖：

<dependencyManagement>
    	<dependencies>
						<dependency>
                <groupId>io.opentelemetry</groupId>
                <artifactId>opentelemetry-bom</artifactId>
                <version>1.7.1</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    
    <dependencies>
        <dependency>
            <groupId>io.opentelemetry</groupId>
            <artifactId>opentelemetry-api</artifactId>
        </dependency>
        <dependency>
            <groupId>io.opentelemetry</groupId>
            <artifactId>opentelemetry-sdk</artifactId>
        </dependency>
        <dependency>
            <groupId>io.opentelemetry</groupId>
            <artifactId>opentelemetry-sdk-trace</artifactId>
        </dependency>
        <dependency>
            <groupId>io.opentelemetry</groupId>
            <artifactId>opentelemetry-exporter-logging</artifactId>
        </dependency>
    </dependencies>

测试代码：

import io.opentelemetry.api.OpenTelemetry;
import io.opentelemetry.api.trace.Span;
import io.opentelemetry.api.trace.SpanBuilder;
import io.opentelemetry.api.trace.SpanKind;
import io.opentelemetry.api.trace.propagation.W3CTraceContextPropagator;
import io.opentelemetry.context.Scope;
import io.opentelemetry.context.propagation.ContextPropagators;
import io.opentelemetry.exporter.logging.LoggingSpanExporter;
import io.opentelemetry.sdk.OpenTelemetrySdk;
import io.opentelemetry.sdk.resources.Resource;
import io.opentelemetry.sdk.trace.SdkTracerProvider;
import io.opentelemetry.sdk.trace.export.BatchSpanProcessor;
import io.opentelemetry.sdk.trace.export.SimpleSpanProcessor;
import io.opentelemetry.sdk.trace.samplers.Sampler;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Date;

public enum Tracer {

    INSTANCE;

    private io.opentelemetry.api.trace.Tracer delegate;

    Tracer() {
        // 创建TracerProvider，可以自定义TraceId，spanId生成规则；采样规则；后端（jaeger,otlp,logging）
        SdkTracerProvider sdkTracerProvider = SdkTracerProvider.builder()
                .setSampler(Sampler.alwaysOn())
                .setResource(Resource.getDefault().toBuilder().put("service.name", serviceName()).build())
                .addSpanProcessor(SimpleSpanProcessor.create(new LoggingSpanExporter()))
                .build();

        OpenTelemetry openTelemetry = OpenTelemetrySdk.builder()
                .setTracerProvider(sdkTracerProvider)
                // 跨进程传播规则
                .setPropagators(ContextPropagators.create(W3CTraceContextPropagator.getInstance()))
                .buildAndRegisterGlobal();
        this.delegate = openTelemetry.getTracer("http-proxy");
    }

    private String serviceName() {
        String hostName = null;
        try {
            hostName = InetAddress.getLocalHost().getHostName();
        } catch (UnknownHostException e) {
            hostName = "unknown";
        }
        return hostName;
    }

    public static SpanBuilder spanBuilder(String s) {
        return INSTANCE.delegate.spanBuilder(s);
    }

    public static void main(String[] args) throws InterruptedException {
        Span root = Tracer.spanBuilder("stream")
                .setSpanKind(SpanKind.SERVER)
                .setAttribute("class",Tracer.class.getSimpleName())
                .startSpan();

        try (Scope scope = root.makeCurrent()) {
            Span span1 = Tracer.spanBuilder("process1")
                    .setSpanKind(SpanKind.SERVER)
                    .startSpan();
            span1.end();
        } finally {
            root.end();
        }
        Thread.sleep(10000000);
    }
}

输出：

12月 12, 2021 11:53:28 上午 io.opentelemetry.exporter.logging.LoggingSpanExporter export
信息: 'process1' : 44706cc954af501b82881a94ee00894c b16e9b02a44596e1 SERVER [tracer: main:] {}
12月 12, 2021 11:53:28 上午 io.opentelemetry.exporter.logging.LoggingSpanExporter export
信息: 'stream' : 44706cc954af501b82881a94ee00894c 797ac60da89b6d0c SERVER [tracer: main:] AttributesMap{data={class=Tracer}, capacity=128, totalAddedValues=1}

使用demo

再看下类图