tessl/maven-com-netflix-hystrix--hystrix-metrics-event-stream

A Netflix Hystrix module that exposes circuit breaker and thread pool metrics in Server-Sent Events format for real-time monitoring and dashboard integration

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Hystrix Metrics Event Stream

Name: tessl/maven-com-netflix-hystrix--hystrix-metrics-event-stream
Author: tessl

Hystrix Metrics Event Stream is a Java library module within the Netflix Hystrix circuit breaker framework that provides real-time streaming of circuit breaker and thread pool metrics via Server-Sent Events (SSE). The module enables monitoring dashboards and applications to receive continuous metric updates including error rates, latency percentiles, circuit breaker states, and thread pool statistics.

Package Information

Package Name: hystrix-metrics-event-stream
Package Type: maven
Language: Java
Installation: Add to Maven dependencies:
```
<dependency>
  <groupId>com.netflix.hystrix</groupId>
  <artifactId>hystrix-metrics-event-stream</artifactId>
  <version>1.5.18</version>
</dependency>
```

Core Imports

// Primary streaming servlets
import com.netflix.hystrix.contrib.metrics.eventstream.HystrixMetricsStreamServlet;
import com.netflix.hystrix.contrib.requests.stream.HystrixRequestEventsSseServlet;
import com.netflix.hystrix.contrib.sample.stream.HystrixConfigSseServlet;
import com.netflix.hystrix.contrib.sample.stream.HystrixUtilizationSseServlet;
import com.netflix.hystrix.contrib.sample.stream.HystrixSampleSseServlet;

// Legacy polling (deprecated)
import com.netflix.hystrix.contrib.metrics.eventstream.HystrixMetricsPoller;

// RxJava Observable types
import rx.Observable;

Basic Usage

The primary use case is to expose Hystrix metrics via HTTP Server-Sent Events:

<!-- Configure in web.xml -->
<servlet>
  <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>

Then access the stream:

curl http://hostname:port/appname/hystrix.stream

This produces continuous JSON events like:

data: {
  "type": "HystrixCommand",
  "name": "PlaylistGet",
  "group": "PlaylistGet",
  "currentTime": 1355239617628,
  "isCircuitBreakerOpen": false,
  "errorPercentage": 0,
  "errorCount": 0,
  "requestCount": 121,
  "latencyExecute_mean": 13,
  "latencyTotal_mean": 15
}

Architecture

The library is organized around several key components:

Servlet Layer: HTTP servlets that implement Server-Sent Events streaming protocol
Poller Layer: Background polling mechanisms for gathering metrics (deprecated)
Stream Processing: RxJava-based reactive streams for real-time data processing
JSON Serialization: Jackson-based JSON encoding of metric data
Connection Management: Configurable concurrent connection limits and throttling

Capabilities

Metrics Streaming

Primary servlet for streaming Hystrix command and thread pool metrics in text/event-stream format.

public class HystrixMetricsStreamServlet extends HystrixSampleSseServlet {
    public HystrixMetricsStreamServlet();
    HystrixMetricsStreamServlet(Observable<HystrixDashboardStream.DashboardData> sampleStream, int pausePollerThreadDelayInMs);
}

Metrics Streaming

Base SSE Servlet Framework

Abstract base class providing Server-Sent Events functionality for all streaming servlets.

public abstract class HystrixSampleSseServlet extends HttpServlet {
    protected HystrixSampleSseServlet(Observable<String> sampleStream);
    protected HystrixSampleSseServlet(Observable<String> sampleStream, int pausePollerThreadDelayInMs);
    
    // Abstract methods for connection management
    protected abstract int getMaxNumberConcurrentConnectionsAllowed();
    protected abstract int getNumberCurrentConnections();
    protected abstract int incrementAndGetCurrentConcurrentConnections();
    protected abstract void decrementCurrentConcurrentConnections();
    
    // Lifecycle methods
    public static void shutdown();
    public void init() throws ServletException;
    public void destroy();
}

Base SSE Framework

Request Events Streaming

Servlet that streams individual Hystrix request events as they occur.

public class HystrixRequestEventsSseServlet extends HystrixSampleSseServlet {
    public HystrixRequestEventsSseServlet();
    HystrixRequestEventsSseServlet(Observable<HystrixRequestEvents> sampleStream, int pausePollerThreadDelayInMs);
}

Request Events Streaming

Configuration Streaming

Servlet that streams Hystrix configuration information.

public class HystrixConfigSseServlet extends HystrixSampleSseServlet {
    public HystrixConfigSseServlet();
    HystrixConfigSseServlet(Observable<HystrixConfiguration> sampleStream, int pausePollerThreadDelayInMs);
}

Configuration Streaming

Utilization Streaming

Servlet that streams current Hystrix command and thread pool utilization metrics.

public class HystrixUtilizationSseServlet extends HystrixSampleSseServlet {
    public HystrixUtilizationSseServlet();
    HystrixUtilizationSseServlet(Observable<HystrixUtilization> sampleStream, int pausePollerThreadDelayInMs);
}

Utilization Streaming

Legacy Metrics Polling (Deprecated)

Polling-based metrics collection system (deprecated since 1.5.4).

@Deprecated
public class HystrixMetricsPoller {
    public HystrixMetricsPoller(MetricsAsJsonPollerListener listener, int delay);
    public synchronized void start();
    public synchronized void pause();
    public synchronized void shutdown();
    public boolean isRunning();
    
    public static interface MetricsAsJsonPollerListener {
        public void handleJsonMetric(String json);
    }
}

Legacy Metrics Polling

Configuration

Connection Limits

All servlets support configurable maximum concurrent connections:

// System property configuration (default: 5)
hystrix.config.stream.maxConcurrentConnections=10

Threading

Default pause delay: 500ms between polling cycles
Uses RxJava IO scheduler for non-blocking stream processing
Atomic connection counting for thread safety

Types

// Core Data Classes
public class HystrixDashboardStream.DashboardData {
    // Contains dashboard metrics for commands and thread pools
}

public interface HystrixRequestEvents {
    // Contains detailed request execution information including events and latencies
}

public interface HystrixConfiguration {
    // Contains complete configuration for commands, thread pools, and collapsers
    Map<HystrixCommandKey, HystrixCommandConfiguration> getCommandConfig();
    Map<HystrixThreadPoolKey, HystrixThreadPoolConfiguration> getThreadPoolConfig();
    Map<HystrixCollapserKey, HystrixCollapserConfiguration> getCollapserConfig();
}

public interface HystrixUtilization {
    // Contains current utilization metrics for commands and thread pools
    Map<HystrixCommandKey, HystrixCommandUtilization> getCommandUtilizationMap();
    Map<HystrixThreadPoolKey, HystrixThreadPoolUtilization> getThreadPoolUtilizationMap();
}

// RxJava Observable Type
public class Observable<T> {
    // Reactive stream for asynchronous data processing
}

// Configuration Properties
public class DynamicIntProperty {
    int get();
}