上一篇文章单独介绍了Ribbon框架的使用，及其如何实现客户端对服务访问的负载均衡，但只是单独从Ribbon框架实现，没有涉及spring cloud。本文着力介绍Ribbon的负载均衡机制，下一篇文章再在spring中继承Ribbon。

Ribbon负载均衡器

上一篇文章我们已经实现了一个客户端负载均衡请求web服务的示例。

当时，我们留了一个伏笔，其中的负载均衡的规则策略可以定制，那么本文着重研究策略定制这部分内容，其他的ribbon客户端的构建和请求方法请参见上一篇文章。

ribbon的负载均衡的策略规则是独立的，即这部分功能可以独立于时间的客户端构造和请求发送。我们需要做的是，实现一个IRule接口的对象，对象里面当然会有一些需要你去覆盖实现的方法，这些方法中需要用代码实现你定制的服务器选择策略，但不包括实际的网络请求操作。

除了可以自己定制，Ribbon已经为我们设计了几个现成的规则策略，分别对应于多个不同IRule实现类。我们只需要将这些类对象传给负载均衡器ILoadBalancer的chooseServer()就可以了。其中，默认情况下，BaseLoadBalancer会选择轮询各个server的策略方式，叫做RoundRobinRule。源码如下：

public class BaseLoadBalancer extends AbstractLoadBalancer implements

        PrimeConnections.PrimeConnectionListener, IClientConfigAware {

    private static Logger logger = LoggerFactory

            .getLogger(BaseLoadBalancer.class);

    private final static IRule DEFAULT_RULE = new RoundRobinRule();

    private final static SerialPingStrategy DEFAULT_PING_STRATEGY = new SerialPingStrategy();

    private static final String DEFAULT_NAME = "default";

    private static final String PREFIX = "LoadBalancer_";

    protected IRule rule = DEFAULT_RULE;

    protected IPingStrategy pingStrategy = DEFAULT_PING_STRATEGY;

    protected IPing ping = null;

    @Monitor(name = PREFIX + "AllServerList", type = DataSourceType.INFORMATIONAL)

    protected volatile List<Server> allServerList = Collections

            .synchronizedList(new ArrayList<Server>());

    @Monitor(name = PREFIX + "UpServerList", type = DataSourceType.INFORMATIONAL)

    protected volatile List<Server> upServerList = Collections

            .synchronizedList(new ArrayList<Server>());

好，先说到这里，我们来实验一下默认的规则策略：

第一步，我们先构建一个负载均衡器，类型BaseLoadBalancer，它是ILoadBalancer的实现类。

负载均衡器，需要配置两样东西：

1、服务地址列表——谁来参选？

2、选择策略规则——怎么选？

第二步，按照服务方的地址端口列表，配置一个Server的List。添加给负载均衡器。

第三步，构造或选择一个IRule实现类，通过ConfigurationMannager来配置【客户端名称】.ribbon.NFLoadBalancerRuleClassName属性，将配置键赋予一个规则类。这里我们不操作，使用默认的。

package com.happybks.invokers;

import java.util.ArrayList;

import java.util.List;

import com.netflix.loadbalancer.BaseLoadBalancer;

import com.netflix.loadbalancer.ILoadBalancer;

import com.netflix.loadbalancer.Server;

public class BalancerApplication {

	public static void main(String[] args) {

		ILoadBalancer balancer=new BaseLoadBalancer();

		List<Server> servers = new ArrayList<Server>();

		servers.add(new Server("127.0.0.1",8091));

		servers.add(new Server("127.0.0.1",8092));

		balancer.addServers(servers);

		for(int i=0;i<10;i++) {

			Server choosedServer = balancer.chooseServer(null);

			System.out.println(choosedServer);

		}

	}

}

默认策略，就用BaseLoadBalancer类默认初始化定义好的，chooseServer方法会为我们选择已有的RoundRobinRule。

（本文出自ochina博主happBKs的博文：https://my.oschina.net/happyBKs/blog/1787825）

源码如下：

private final static IRule DEFAULT_RULE = new RoundRobinRule();

    /*

     * Get the alive server dedicated to key

     *

     * @return the dedicated server

     */

    public Server chooseServer(Object key) {

        if (counter == null) {

            counter = createCounter();

        }

        counter.increment();

        if (rule == null) {

            return null;

        } else {

            try {

                return rule.choose(key);

            } catch (Exception e) {

                logger.warn("LoadBalancer [{}]:  Error choosing server for key {}", name, key, e);

                return null;

            }

        }

    }

我们运行代码：10次选择server的结果打印如下：

16:41:10.754 [main] WARN com.netflix.config.sources.URLConfigurationSource - No URLs will be polled as dynamic configuration sources.

16:41:10.758 [main] INFO com.netflix.config.sources.URLConfigurationSource - To enable URLs as dynamic configuration sources, define System property archaius.configurationSource.additionalUrls or make config.properties available on classpath.

16:41:10.766 [main] INFO com.netflix.config.DynamicPropertyFactory - DynamicPropertyFactory is initialized with configuration sources: com.netflix.config.ConcurrentCompositeConfiguration@75bd9247

16:41:10.818 [main] DEBUG com.netflix.loadbalancer.BaseLoadBalancer - LoadBalancer [default]: clearing server list (SET op)

16:41:10.819 [main] DEBUG com.netflix.loadbalancer.BaseLoadBalancer - LoadBalancer [default]:  addServer [127.0.0.1:8091]

16:41:10.819 [main] DEBUG com.netflix.loadbalancer.BaseLoadBalancer - LoadBalancer [default]:  addServer [127.0.0.1:8092]

127.0.0.1:8092

127.0.0.1:8091

127.0.0.1:8092

127.0.0.1:8091

127.0.0.1:8092

127.0.0.1:8091

127.0.0.1:8092

127.0.0.1:8091

127.0.0.1:8092

127.0.0.1:8091

关于负载均衡相关的四个配置项

这些配置项的前缀是【客户端名称】.ribbon

The supported properties are listed below and should be prefixed by <clientName>.ribbon.:

NFLoadBalancerClassName: should implement ILoadBalancer
NFLoadBalancerRuleClassName: should implement IRule
NFLoadBalancerPingClassName: should implement IPing
NIWSServerListClassName: should implement ServerList
NIWSServerListFilterClassName should implement ServerListFilter

其中比较重要的是NFLoadBalancerRuleClassName，我们可以通过这个配置项定制需要的负载均衡规则，可以是ribbon提供的原生的几种规则类，也可以是自己实现的规则类，这些类都实现了IRule接口。

NFLoadBalancerPingClassName用于配置查看服务器是否存活。

NFLoadBalancerRuleClassName指定负载均衡器的实现类。当然，可以设置自己实现的负载均衡器。

NIWSServerListClassName是服务器列表的处理类，用来维护服务器列表的。Ribbon已经实现了动态服务器列表。

NIWSServerListFilterClassName是服务器的拦截类。

负载均衡的两种配置方法：

一种直接调用ConfigurationManager获取配置实例，然后设置配置属性；一种是在application.yml中配置。

自定义策略规则：

下面我们以一个示例来构建一个自己的负载均衡规则。

示例：构建一个60%的概率选择8091,40%概率选择8092的规则

我们构建一个实现IRule接口的实现类：

package com.happybks.invokers;

import java.util.List;

import java.util.Random;

import com.netflix.loadbalancer.BaseLoadBalancer;

import com.netflix.loadbalancer.ILoadBalancer;

import com.netflix.loadbalancer.IRule;

import com.netflix.loadbalancer.Server;

public class MyProbabilityRandomRule implements IRule {

	ILoadBalancer balancer = new BaseLoadBalancer();

	@Override

	public Server choose(Object key) {

		List<Server> allServers = balancer.getAllServers();

		Random random = new Random();

		final int number = random.nextInt(10);

		if (number < 7) {

			return findServer(allServers,8091);

		}

		return findServer(allServers,8092);

	}

	private Server findServer(List<Server> allServers, int port) {

		for (Server server : allServers) {

			if (server.getPort() == port) {

				return server;

			}

		}

		System.out.println("NULL port="+port);

		return null;

	}

	@Override

	public void setLoadBalancer(ILoadBalancer lb) {

		this.balancer = lb;

	}

	@Override

	public ILoadBalancer getLoadBalancer() {

		return this.balancer;

	}

}

客户端的请求程序这里我们还是直接在一个普通的main方法中实现

我们首先需要配置请求服务器列表，这个上篇文章已经介绍过。

之后我们对对应的客户端配置它的ribbon.NFLoadBalancerRuleClassName配置为我们刚才定义的那个实现了IRule的实现类的类名全名，注意：是IRule实现类的全名，一个字符串，不是class。

package com.happybks.invokers;

import com.netflix.client.ClientException;

import com.netflix.client.ClientFactory;

import com.netflix.client.http.HttpRequest;

import com.netflix.client.http.HttpResponse;

import com.netflix.config.ConfigurationManager;

import com.netflix.niws.client.http.RestClient;

public class MyRuleClientApplication {

	public static void main(String[] args) throws Exception {

		// 1、设置请求的服务器

		ConfigurationManager.getConfigInstance().setProperty("happybks-client.ribbon.listOfServers",

				"localhost:8091,localhost:8092"); // 1

		// 2、 配置规则处理类

		//本示例略，先默认使用其默认负载均衡策略规则

		ConfigurationManager.getConfigInstance().setProperty("happybks-client.ribbon.NFLoadBalancerRuleClassName",MyProbabilityRandomRule.class.getName());

		// 3、获取 REST 请求客户端

		RestClient client = (RestClient) ClientFactory.getNamedClient("happybks-client");

		// 4、创建请求实例

		HttpRequest request = HttpRequest.newBuilder().uri("/carsInfo/onsale").build();

		// 5、发 送 10 次请求到服务器中

		for (int i = 0; i < 10; i++) {

			System.out.println("the "+(i+1)+"th: ");

			HttpResponse response = client.executeWithLoadBalancer(request);

			String result = response.getEntity(String.class);

			System.out.println(result);

		}

	}

}

响应请求的服务方程序请参见之前的文章，我们不再累述。然后我们看看运行结果：

22:52:27.695 [main] WARN com.netflix.config.sources.URLConfigurationSource - No URLs will be polled as dynamic configuration sources.

22:52:27.701 [main] INFO com.netflix.config.sources.URLConfigurationSource - To enable URLs as dynamic configuration sources, define System property archaius.configurationSource.additionalUrls or make config.properties available on classpath.

22:52:27.834 [main] INFO com.netflix.config.DynamicPropertyFactory - DynamicPropertyFactory is initialized with configuration sources: com.netflix.config.ConcurrentCompositeConfiguration@97e1986

22:52:28.787 [main] INFO com.netflix.http4.ConnectionPoolCleaner - Initializing ConnectionPoolCleaner for NFHttpClient:happybks-client

22:52:28.798 [Connection pool clean up thread] DEBUG com.netflix.http4.ConnectionPoolCleaner - Connection pool clean up started for client happybks-client

22:52:28.799 [Connection pool clean up thread] DEBUG com.netflix.http4.MonitoredConnectionManager - Closing expired connections

22:52:28.799 [Connection pool clean up thread] DEBUG com.netflix.http4.NamedConnectionPool - Closing expired connections

22:52:28.799 [Connection pool clean up thread] DEBUG com.netflix.http4.MonitoredConnectionManager - Closing connections idle longer than 30000 MILLISECONDS

22:52:28.800 [Connection pool clean up thread] DEBUG com.netflix.http4.NamedConnectionPool - Closing connections idle longer than 30000 MILLISECONDS

22:52:29.032 [main] WARN com.netflix.client.ClientFactory - Class com.happybks.invokers.MyProbabilityRandomRule neither implements IClientConfigAware nor provides a constructor with IClientConfig as the parameter. Only default constructor will be used.

22:52:29.035 [main] INFO com.netflix.loadbalancer.BaseLoadBalancer - Client: happybks-client instantiated a LoadBalancer: DynamicServerListLoadBalancer:{NFLoadBalancer:name=happybks-client,current list of Servers=[],Load balancer stats=Zone stats: {},Server stats: []}ServerList:null

22:52:29.111 [main] INFO com.netflix.loadbalancer.DynamicServerListLoadBalancer - Using serverListUpdater PollingServerListUpdater

22:52:29.145 [main] WARN com.netflix.client.ClientFactory - Class com.happybks.invokers.MyProbabilityRandomRule neither implements IClientConfigAware nor provides a constructor with IClientConfig as the parameter. Only default constructor will be used.

22:52:29.165 [main] INFO com.netflix.loadbalancer.DynamicServerListLoadBalancer - DynamicServerListLoadBalancer for client happybks-client initialized: DynamicServerListLoadBalancer:{NFLoadBalancer:name=happybks-client,current list of Servers=[localhost:8091, localhost:8092],Load balancer stats=Zone stats: {unknown=[Zone:unknown;	Instance count:2;	Active connections count: 0;	Circuit breaker tripped count: 0;	Active connections per server: 0.0;]

},Server stats: [[Server:localhost:8092;	Zone:UNKNOWN;	Total Requests:0;	Successive connection failure:0;	Total blackout seconds:0;	Last connection made:Thu Jan 01 08:00:00 GMT+08:00 1970;	First connection made: Thu Jan 01 08:00:00 GMT+08:00 1970;	Active Connections:0;	total failure count in last (1000) msecs:0;	average resp time:0.0;	90 percentile resp time:0.0;	95 percentile resp time:0.0;	min resp time:0.0;	max resp time:0.0;	stddev resp time:0.0]

, [Server:localhost:8091;	Zone:UNKNOWN;	Total Requests:0;	Successive connection failure:0;	Total blackout seconds:0;	Last connection made:Thu Jan 01 08:00:00 GMT+08:00 1970;	First connection made: Thu Jan 01 08:00:00 GMT+08:00 1970;	Active Connections:0;	total failure count in last (1000) msecs:0;	average resp time:0.0;	90 percentile resp time:0.0;	95 percentile resp time:0.0;	min resp time:0.0;	max resp time:0.0;	stddev resp time:0.0]

]}ServerList:com.netflix.loadbalancer.ConfigurationBasedServerList@152aa092

22:52:29.165 [main] INFO com.netflix.client.ClientFactory - Client: happybks-client instantiated a LoadBalancer: DynamicServerListLoadBalancer:{NFLoadBalancer:name=happybks-client,current list of Servers=[localhost:8091, localhost:8092],Load balancer stats=Zone stats: {unknown=[Zone:unknown;	Instance count:2;	Active connections count: 0;	Circuit breaker tripped count: 0;	Active connections per server: 0.0;]

},Server stats: [[Server:localhost:8092;	Zone:UNKNOWN;	Total Requests:0;	Successive connection failure:0;	Total blackout seconds:0;	Last connection made:Thu Jan 01 08:00:00 GMT+08:00 1970;	First connection made: Thu Jan 01 08:00:00 GMT+08:00 1970;	Active Connections:0;	total failure count in last (1000) msecs:0;	average resp time:0.0;	90 percentile resp time:0.0;	95 percentile resp time:0.0;	min resp time:0.0;	max resp time:0.0;	stddev resp time:0.0]

, [Server:localhost:8091;	Zone:UNKNOWN;	Total Requests:0;	Successive connection failure:0;	Total blackout seconds:0;	Last connection made:Thu Jan 01 08:00:00 GMT+08:00 1970;	First connection made: Thu Jan 01 08:00:00 GMT+08:00 1970;	Active Connections:0;	total failure count in last (1000) msecs:0;	average resp time:0.0;	90 percentile resp time:0.0;	95 percentile resp time:0.0;	min resp time:0.0;	max resp time:0.0;	stddev resp time:0.0]

]}ServerList:com.netflix.loadbalancer.ConfigurationBasedServerList@152aa092

22:52:29.167 [main] INFO com.netflix.client.ClientFactory - Client Registered:com.netflix.niws.client.http.RestClient@44a7bfbc

the 1th:

22:52:30.115 [PollingServerListUpdater-0] DEBUG com.netflix.loadbalancer.DynamicServerListLoadBalancer - List of Servers for happybks-client obtained from Discovery client: [localhost:8091, localhost:8092]

22:52:30.115 [PollingServerListUpdater-0] DEBUG com.netflix.loadbalancer.DynamicServerListLoadBalancer - Filtered List of Servers for happybks-client obtained from Discovery client: [localhost:8091, localhost:8092]

22:52:30.115 [PollingServerListUpdater-0] DEBUG com.netflix.loadbalancer.BaseLoadBalancer - LoadBalancer [happybks-client]: clearing server list (SET op)

22:52:30.115 [PollingServerListUpdater-0] DEBUG com.netflix.loadbalancer.BaseLoadBalancer - LoadBalancer [happybks-client]:  addServer [localhost:8091]

22:52:30.115 [PollingServerListUpdater-0] DEBUG com.netflix.loadbalancer.BaseLoadBalancer - LoadBalancer [happybks-client]:  addServer [localhost:8092]

22:52:30.115 [PollingServerListUpdater-0] DEBUG com.netflix.loadbalancer.DynamicServerListLoadBalancer - Setting server list for zones: {unknown=[localhost:8091, localhost:8092]}

22:52:30.115 [PollingServerListUpdater-0] DEBUG com.netflix.loadbalancer.BaseLoadBalancer - LoadBalancer [happybks-client_unknown]: clearing server list (SET op)

22:52:30.115 [PollingServerListUpdater-0] DEBUG com.netflix.loadbalancer.BaseLoadBalancer - LoadBalancer [happybks-client_unknown]:  addServer [localhost:8091]

22:52:30.115 [PollingServerListUpdater-0] DEBUG com.netflix.loadbalancer.BaseLoadBalancer - LoadBalancer [happybks-client_unknown]:  addServer [localhost:8092]

{"brandName":"Volvo","price":536000.0,"serviceUrl":"http://localhost:8092/carsInfo/onsale"}

the 2th:

{"brandName":"Volvo","price":536000.0,"serviceUrl":"http://localhost:8091/carsInfo/onsale"}

the 3th:

{"brandName":"Volvo","price":536000.0,"serviceUrl":"http://localhost:8091/carsInfo/onsale"}

the 4th:

{"brandName":"Volvo","price":536000.0,"serviceUrl":"http://localhost:8091/carsInfo/onsale"}

the 5th:

andName":"Volvo","price":536000.0,"serviceUrl":"http://localhost:8091/carsInfo/onsale"}

the 6th:

{"brandName":"Volvo","price":536000.0,"serviceUrl":"http://localhost:8092/carsInfo/onsale"}

the 7th:

andName":"Volvo","price":536000.0,"serviceUrl":"http://localhost:8092/carsInfo/onsale"}

the 8th:

{"brandName":"Volvo","price":536000.0,"serviceUrl":"http://localhost:8091/carsInfo/onsale"}

the 9th:

{"brandName":"Volvo","price":536000.0,"serviceUrl":"http://localhost:8092/carsInfo/onsale"}

the 10th:

{"brandName":"Volvo","price":536000.0,"serviceUrl":"http://localhost:8091/carsInfo/onsale"}

22:52:30.889 [Thread-2] INFO com.netflix.loadbalancer.PollingServerListUpdater - Shutting down the Executor Pool for PollingServerListUpdater

从上面的结果可以看出，有6个请求为8091，剩下4个为8092，我们自己定义的规则的功能就实现了。

Ribbon内置负载均衡规则

Ribbon框架按照不同需求，已经为我们实现了许多实现了IRule接口的实现类，适用于常用的负载均衡规则。以下规则能够实现大部分负载均衡需求的应用场景，如果有更复杂的需求，可以自己实现IRule。

内置负载均衡规则类	规则描述
RoundRobinRule	简单轮询服务列表来选择服务器。它是Ribbon默认的负载均衡规则。
AvailabilityFilteringRule	对以下两种服务器进行忽略：（1）在默认情况下，这台服务器如果3次连接失败，这台服务器就会被设置为“短路”状态。短路状态将持续30秒，如果再次连接失败，短路的持续时间就会几何级地增加。注意：可以通过修改配置loadbalancer.<clientName>.connectionFailureCountThreshold来修改连接失败多少次之后被设置为短路状态。默认是3次。（2）并发数过高的服务器。如果一个服务器的并发连接数过高，配置了AvailabilityFilteringRule规则的客户端也会将其忽略。并发连接数的上线，可以由客户端的<clientName>.<clientConfigNameSpace>.ActiveConnectionsLimit属性进行配置。
WeightedResponseTimeRule	为每一个服务器赋予一个权重值。服务器响应时间越长，这个服务器的权重就越小。这个规则会随机选择服务器，这个权重值会影响服务器的选择。
ZoneAvoidanceRule	以区域可用的服务器为基础进行服务器的选择。使用Zone对服务器进行分类，这个Zone可以理解为一个机房、一个机架等。
BestAvailableRule	忽略哪些短路的服务器，并选择并发数较低的服务器。
RandomRule	随机选择一个可用的服务器。
Retry	重试机制的选择逻辑

附录：AvailabilityFilteringRule的三个默认配置

# successive connection failures threshold to put the server in circuit tripped state, default 3

niws.loadbalancer.<clientName>.connectionFailureCountThreshold

# Maximal period that an instance can remain in "unusable" state regardless of the exponential increase, default 30

niws.loadbalancer.<clientName>.circuitTripMaxTimeoutSeconds

# threshold of concurrent connections count to skip the server, default is Integer.MAX_INT

<clientName>.<clientConfigNameSpace>.ActiveConnectionsLimit

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apt-get/dpkg常用指令备查
apt-get install <package> Downloads <package> and all of its dependencies, and installs ...
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mybatis 之 parameterType="java.util.HashMap">
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N76E003之WDT（看门狗定时器）
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使用java中的session来记录访问次数
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URL地址重写例子(Helicon)
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iOS开发——iOS7（及以后版本） SDK自带二维码（含条形码）扫码、二维码生成
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Python进阶学习笔记（一）
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