spring-cloud-sleuth+zipkin源码探究

老梁

发布于 2019-09-10 18:35:36

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发布于 2019-09-10 18:35:36

文章被收录于专栏：Java工程师成长之路Java工程师成长之路

1. spring-cloud-sleuth+zipkin源码探究

1.1. 前言

粗略看了下spring cloud sleuth core源码，发现内容真的有点多，它支持了很多类型的链路追踪，我就找其中一个比较有代表性的深入剖析下源码结构和内容

1.2. spring-cloud-sleuth-core源码解析

1.2.1. 结构

可以看到源码中支持的追踪类型有很多，支持async，hystrix，websocket，rxjava，Spring mvc，servlet，spring restTemplate，feign，zuul等等，这里我着重探讨spring web mvc的链路追踪
打开web包，找到TraceWebAutoConfiguration，这里配置了主要的初始化类

1.2.2. 过滤器注册

当启动初始化程序时，跟踪代码如下

    @Bean
    public FilterRegistrationBean traceWebFilter(TraceFilter traceFilter) {
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(
                traceFilter);
        filterRegistrationBean.setDispatcherTypes(ASYNC, ERROR, FORWARD, INCLUDE,
                REQUEST);
        filterRegistrationBean.setOrder(TraceFilter.ORDER);
        return filterRegistrationBean;
    }

    @Bean
    @ConditionalOnMissingBean
    public TraceFilter traceFilter(BeanFactory beanFactory,
            SkipPatternProvider skipPatternProvider) {
        return new TraceFilter(beanFactory, skipPatternProvider.skipPattern());
    }

初始化traceFilter，进行过滤器注册

1.2.3. 拦截器注册

然后看TraceWebMvcConfigurer类，它会进行拦截器的注册

@Configuration
class TraceWebMvcConfigurer extends WebMvcConfigurerAdapter {
    @Autowired BeanFactory beanFactory;

    @Bean
    public TraceHandlerInterceptor traceHandlerInterceptor(BeanFactory beanFactory) {
        return new TraceHandlerInterceptor(beanFactory);
    }

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(this.beanFactory.getBean(TraceHandlerInterceptor.class));
    }
}

在TraceHandlerInterceptor类中，preHandle,afterCompletion方法可以看出，这是对请求进行拦截进行span的包装

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
            Object handler) throws Exception {
        String spanName = spanName(handler);
        boolean continueSpan = getRootSpanFromAttribute(request) != null;
        Span span = continueSpan ? getRootSpanFromAttribute(request) : getTracer().createSpan(spanName);
        if (log.isDebugEnabled()) {
            log.debug("Handling span " + span);
        }
        addClassMethodTag(handler, span);
        addClassNameTag(handler, span);
        setSpanInAttribute(request, span);
        if (!continueSpan) {
            setNewSpanCreatedAttribute(request, span);
        }
        return true;
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response,
            Object handler, Exception ex) throws Exception {
        if (isErrorControllerRelated(request)) {
            if (log.isDebugEnabled()) {
                log.debug("Skipping closing of a span for error controller processing");
            }
            return;
        }
        Span span = getRootSpanFromAttribute(request);
        if (ex != null) {
            getErrorParser().parseErrorTags(span, ex);
        }
        if (getNewSpanFromAttribute(request) != null) {
            if (log.isDebugEnabled()) {
                log.debug("Closing span " + span);
            }
            Span newSpan = getNewSpanFromAttribute(request);
            getTracer().continueSpan(newSpan);
            getTracer().close(newSpan);
            clearNewSpanCreatedAttribute(request);
        }
    }

1.2.4. zipkin端点提交

这里首先会初始化HttpZipkinSpanReporter类，，用来进行span端点提交，然后初始化ZipkinSpanListenerspan的监听器，用来监听并调用端点提交，以上配置再下图位置

1.2.5. 调用http接口时，进入过滤器

首先进入TraceFilter中的过滤方法doFilter，这里会做span的创建

private Span createSpan(HttpServletRequest request,
            boolean skip, Span spanFromRequest, String name) {
        if (spanFromRequest != null) {
            if (log.isDebugEnabled()) {
                log.debug("Span has already been created - continuing with the previous one");
            }
            return spanFromRequest;
        }
        //加入调用链路ZipkinHttpSpanExtractor，此链路在TraceHttpAutoConfiguration中配置实例化，调用链还没有时，返回为空，作为头节点
        Span parent = spanExtractor().joinTrace(new HttpServletRequestTextMap(request));
        if (parent != null) {
            if (log.isDebugEnabled()) {
                log.debug("Found a parent span " + parent + " in the request");
            }
            addRequestTagsForParentSpan(request, parent);
            spanFromRequest = parent;
            tracer().continueSpan(spanFromRequest);
            if (parent.isRemote()) {
                parent.logEvent(Span.SERVER_RECV);
            }
            request.setAttribute(TRACE_REQUEST_ATTR, spanFromRequest);
            if (log.isDebugEnabled()) {
                log.debug("Parent span is " + parent + "");
            }
        } else {
            if (skip) {
                spanFromRequest = tracer().createSpan(name, NeverSampler.INSTANCE);
            }
            else {
                String header = request.getHeader(Span.SPAN_FLAGS);
                if (Span.SPAN_SAMPLED.equals(header)) {
                    spanFromRequest = tracer().createSpan(name, new AlwaysSampler());
                } else {
                //创建span节点
                    spanFromRequest = tracer().createSpan(name);
                }
            }
            spanFromRequest.logEvent(Span.SERVER_RECV);
            request.setAttribute(TRACE_REQUEST_ATTR, spanFromRequest);
            if (log.isDebugEnabled()) {
                log.debug("No parent span present - creating a new span");
            }
        }
        return spanFromRequest;
    }