hystrix dashboard Unable to connect to Command Metric Stream解决办法

spring cloud 在初次使用 hystrix dashboard仪表盘的时候很容易出现hystrix dashboard Unable to connect to Command Metric Stream错误

如下图：

首先查看依赖时候添加全

<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-hystrix-dashboard</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

其次启动程序注解是否添加

@EnableCircuitBreaker
@EnableHystrixDashboard

如果都没问题那么检查下springboot 版本如果是2.0则需要添加 ServletRegistrationBean 因为springboot的默认路径不是 "/hystrix.stream"，只要在自己的项目里配置上下面的servlet就可以了

@Bean
public ServletRegistrationBean getServlet() {
HystrixMetricsStreamServlet streamServlet = new HystrixMetricsStreamServlet();
ServletRegistrationBean registrationBean = new ServletRegistrationBean(streamServlet);
registrationBean.setLoadOnStartup(1);
registrationBean.addUrlMappings("/hystrix.stream");
registrationBean.setName("HystrixMetricsStreamServlet");
return registrationBean;
}

修改完成重启服务问题便会解决

分析：

首先，查看源码中 类 HystrixStreamEndpoint 从中可以看到 new EndpointServlet(HystrixMetricsStreamServlet.class）

package org.springframework.cloud.netflix.hystrix;

import com.netflix.hystrix.contrib.metrics.eventstream.HystrixMetricsStreamServlet;
import java.util.Map;
import java.util.function.Supplier;
import org.springframework.boot.actuate.endpoint.web.EndpointServlet;
import org.springframework.boot.actuate.endpoint.web.annotation.ServletEndpoint;

@ServletEndpoint(
id = "hystrix.stream"
)
public class HystrixStreamEndpoint implements Supplier<EndpointServlet> {
private final Map<String, String> initParameters;

public HystrixStreamEndpoint(Map<String, String> initParameters) {
this.initParameters = initParameters;
}

public EndpointServlet get() {
return (new EndpointServlet(HystrixMetricsStreamServlet.class)).withInitParameters(this.initParameters);
}
}

然后，我们再查看 HystrixMetricsStreamServlet 这个类 在方法的注释中我们可以看到

有提示 “Adding the following to web.xml”

而在springboot中是采用bean的形式配置就可以解决问题了

package com.netflix.hystrix.contrib.metrics.eventstream;

import com.netflix.config.DynamicIntProperty;
import com.netflix.config.DynamicPropertyFactory;
import com.netflix.hystrix.contrib.sample.stream.HystrixSampleSseServlet;
import com.netflix.hystrix.metric.consumer.HystrixDashboardStream;
import com.netflix.hystrix.serial.SerialHystrixDashboardData;
import rx.Observable;
import rx.functions.Func1;

import java.util.concurrent.atomic.AtomicInteger;

/**
* Streams Hystrix metrics in text/event-stream format.
* <p>
* Install by:
* <p>
* 1) Including hystrix-metrics-event-stream-*.jar in your classpath.
* <p>
* 2) Adding the following to web.xml:
* <pre>{@code
* <servlet>
*  <description></description>
*  <display-name>HystrixMetricsStreamServlet</display-name>
*  <servlet-name>HystrixMetricsStreamServlet</servlet-name>
*  <servlet-class>com.netflix.hystrix.contrib.metrics.eventstream.HystrixMetricsStreamServlet</servlet-class>
* </servlet>
* <servlet-mapping>
*  <servlet-name>HystrixMetricsStreamServlet</servlet-name>
*  <url-pattern>/hystrix.stream</url-pattern>
* </servlet-mapping>
* } </pre>
*/
public class HystrixMetricsStreamServlet extends HystrixSampleSseServlet {

private static final long serialVersionUID = -7548505095303313237L;

/* used to track number of connections and throttle */
private static AtomicInteger concurrentConnections = new AtomicInteger(0);
private static DynamicIntProperty maxConcurrentConnections =
DynamicPropertyFactory.getInstance().getIntProperty("hystrix.config.stream.maxConcurrentConnections", 5);

public HystrixMetricsStreamServlet() {
this(HystrixDashboardStream.getInstance().observe(), DEFAULT_PAUSE_POLLER_THREAD_DELAY_IN_MS);
}

/* package-private */ HystrixMetricsStreamServlet(Observable<HystrixDashboardStream.DashboardData> sampleStream, int pausePollerThreadDelayInMs) {
super(sampleStream.concatMap(new Func1<HystrixDashboardStream.DashboardData, Observable<String>>() {
@Override
public Observable<String> call(HystrixDashboardStream.DashboardData dashboardData) {
return Observable.from(SerialHystrixDashboardData.toMultipleJsonStrings(dashboardData));
}
}), pausePollerThreadDelayInMs);
}

@Override
protected int getMaxNumberConcurrentConnectionsAllowed() {
return maxConcurrentConnections.get();
}

@Override
protected int getNumberCurrentConnections() {
return concurrentConnections.get();
}

@Override
protected int incrementAndGetCurrentConcurrentConnections() {
return concurrentConnections.incrementAndGet();
}

@Override
protected void decrementCurrentConcurrentConnections() {
concurrentConnections.decrementAndGet();
}
}