hystrix MaxConcurrentConnections reached 异常

报错1

2017-03-28 10:04:47.438 ERROR 1035 --- [InstanceMonitor] c.n.t.monitor.instance.InstanceMonitor   : Could not initiate connection to host, giving up: [{"timestamp":1490666687435,"status":503,"error":"Service Unavailable","message":"MaxConcurrentConnections reached: 5","path":"/hystrix.stream"}]

~/.m2/repository/com/netflix/hystrix/hystrix-metrics-event-stream/1.5.6/hystrix-metrics-event-stream-1.5.6-sources.jar!/com/netflix/hystrix/contrib/requests/stream/HystrixRequestEventsSseServlet.java

public class HystrixRequestEventsSseServlet extends HystrixSampleSseServlet {

    private static final long serialVersionUID = 6389353893099737870L;

    /* 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);
    //......
}            

~/.m2/repository/com/netflix/hystrix/hystrix-metrics-event-stream/1.5.6/hystrix-metrics-event-stream-1.5.6-sources.jar!/com/netflix/hystrix/contrib/sample/stream/HystrixSampleSseServlet.java

/**
     * - maintain an open connection with the client
     * - on initial connection send latest data of each requested event type
     * - subsequently send all changes for each requested event type
     *
     * @param request  incoming HTTP Request
     * @param response outgoing HTTP Response (as a streaming response)
     * @throws javax.servlet.ServletException
     * @throws java.io.IOException
     */
    private void handleRequest(HttpServletRequest request, final HttpServletResponse response) throws ServletException, IOException {
        final AtomicBoolean moreDataWillBeSent = new AtomicBoolean(true);
        Subscription sampleSubscription = null;

        /* ensure we aren't allowing more connections than we want */
        int numberConnections = incrementAndGetCurrentConcurrentConnections();
        try {
            int maxNumberConnectionsAllowed = getMaxNumberConcurrentConnectionsAllowed(); //may change at runtime, so look this up for each request
            if (numberConnections > maxNumberConnectionsAllowed) {
                response.sendError(503, "MaxConcurrentConnections reached: " + maxNumberConnectionsAllowed);
            } else {
                /* initialize response */
                response.setHeader("Content-Type", "text/event-stream;charset=UTF-8");
                response.setHeader("Cache-Control", "no-cache, no-store, max-age=0, must-revalidate");
                response.setHeader("Pragma", "no-cache");

                final PrintWriter writer = response.getWriter();

                //since the sample stream is based on Observable.interval, events will get published on an RxComputation thread
                //since writing to the servlet response is blocking, use the Rx IO thread for the write that occurs in the onNext
                sampleSubscription = sampleStream
                        .observeOn(Schedulers.io())
                        .subscribe(new Subscriber<String>() {
                            @Override
                            public void onCompleted() {
                                logger.error("HystrixSampleSseServlet: ({}) received unexpected OnCompleted from sample stream", getClass().getSimpleName());
                                moreDataWillBeSent.set(false);
                            }

                            @Override
                            public void onError(Throwable e) {
                                moreDataWillBeSent.set(false);
                            }

                            @Override
                            public void onNext(String sampleDataAsString) {
                                if (sampleDataAsString != null) {
                                    try {
                                        writer.print("data: " + sampleDataAsString + "\n\n");
                                        // explicitly check for client disconnect - PrintWriter does not throw exceptions
                                        if (writer.checkError()) {
                                            throw new IOException("io error");
                                        }
                                        writer.flush();
                                    } catch (IOException ioe) {
                                        moreDataWillBeSent.set(false);
                                    }
                                }
                            }
                        });

                while (moreDataWillBeSent.get() && !isDestroyed) {
                    try {
                        Thread.sleep(pausePollerThreadDelayInMs);
                    } catch (InterruptedException e) {
                        moreDataWillBeSent.set(false);
                    }
                }
            }
        } finally {
            decrementCurrentConcurrentConnections();
            if (sampleSubscription != null && !sampleSubscription.isUnsubscribed()) {
                sampleSubscription.unsubscribe();
            }
        }
    }

报错2

10:45:53.194 INFO [http-nio-9002-exec-393] Caller+0     at org.springframework.cloud.netflix.hystrix.dashboard.HystrixDashboardConfiguration$ProxyStreamServlet.doGet(HystrixDashboardConfiguration.java:165)
 - 

Proxy opening connection to: http://localhost:9002/hystrix.stream


2017-03-28 10:45:53.209  WARN 1404 --- [o-9002-exec-393] ashboardConfiguration$ProxyStreamServlet : Failed opening connection to http://localhost:9002/hystrix.stream : 503 : HTTP/1.1 503 
10:45:53.209 WARN [http-nio-9002-exec-393] Caller+0     at org.springframework.cloud.netflix.hystrix.dashboard.HystrixDashboardConfiguration$ProxyStreamServlet.doGet(HystrixDashboardConfiguration.java:212)
 - Failed opening connection to http://localhost:9002/hystrix.stream : 503 : HTTP/1.1 503 
2017-03-28 10:45:53.209  WARN 1404 --- [o-9002-exec-391] ashboardConfiguration$ProxyStreamServlet : Failed opening connection to http://localhost:9002/hystrix.stream : 503 : HTTP/1.1 503 
10:45:53.209 WARN [http-nio-9002-exec-391] Caller+0     at org.springframework.cloud.netflix.hystrix.dashboard.HystrixDashboardConfiguration$ProxyStreamServlet.doGet(HystrixDashboardConfiguration.java:212)
 - Failed opening connection to http://localhost:9002/hystrix.stream : 503 : HTTP/1.1 503 

curl一下

➜  ~ curl -i http://localhost:9002/hystrix.stream
HTTP/1.1 503
X-Application-Context: recommend:9002
Content-Type: application/json;charset=UTF-8
Transfer-Encoding: chunked
Date: Tue, 28 Mar 2017 02:48:23 GMT
Connection: close

{"timestamp":1490669303758,"status":503,"error":"Service Unavailable","message":"MaxConcurrentConnections reached: 20","path":"/hystrix.stream"}%

如果出现请求/hystrix.stream一直阻塞，或者报错Unable to connect to Command Metric Stream，表示你没有配置HystrixCommand。

解决方案

hystrix.config.stream.maxConcurrentConnections: 50