负载均衡
服务器端负载均衡分为算法包括:轮循算法(Round Robin)、哈希算法(HASH)、响应速度算法(Response Time)、加权法(Weighted )等。网上有文章提到“最少连接算法(Least Connection)”也是负载均衡算法的一种,当然,这样说是需要有前提条件的,就是当服务器性能良好,可以及时处理所有请求的时候,最少连接算法才能达到负载均衡的目的,否则最少连接的服务器可能正在处理比较耗时的操作,继续将请求分发到该服务器可能导致该服务器load值升高,性能下降。参见https://devcentral.f5.com/articles/back-to-basics-least-connections-is-not-least-loaded 。之后我会写关于负载均衡各类算法的博客。
ZK实现负载均衡 使用zk做负载均衡,需要在zk上指定path下注册提供服务的集群中每个节点的ip地址,消费者需要在该path上注册watcher,当服务提供者集群中增删几点时,zk会发起watcher通知,所有消费者都会收到该watcher回调,此时,消费者可以及时知晓服务提供者集群中节点状况,在可用服务器列表中进行负载均衡计算。
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 package org.zk.loadbalance;import com.java.roundrrobin.RoundRobin;import org.apache.zookeeper.KeeperException;import org.apache.zookeeper.WatchedEvent;import org.apache.zookeeper.Watcher;import org.apache.zookeeper.ZooKeeper;import org.junit.Before;import java.io.IOException;import java.util.List;import java.util.concurrent.CountDownLatch; * @auth zhengzhi.ren * @date 2015/7/27. */ public class LoadBalance { private ZooKeeper zkConn; private String path = "/dubbo/org.zk.naming.HelloWorldService/provider" ; private String connectionString = "127.0.0.1:2181" ; private int timeout = 5000 ; private List<String> hosts; private RoundRobin<String> roundRobin = new RoundRobin<String>(hosts); @Before public void connect () { try { final CountDownLatch semaphore = new CountDownLatch(1 ); zkConn = new ZooKeeper(connectionString, timeout, new Watcher() { @Override public void process (WatchedEvent e) { if (e.getState() == Event.KeeperState.SyncConnected){ if (e.getType() == Event.EventType.None && e.getPath() == null ){ System.out.println("Connect success!" ); semaphore.countDown(); } } } }); semaphore.await(); } catch (IOException e) { e.printStackTrace(); } catch (InterruptedException e) { e.printStackTrace(); } } private void registry () { try { hosts = zkConn.getChildren(this .path, new NodeChildrenChangedWatcher()); } catch (KeeperException e) { e.printStackTrace(); } catch (InterruptedException e) { e.printStackTrace(); } } public String get () { return roundRobin.iterator().next(); } class NodeChildrenChangedWatcher implements Watcher { @Override public void process (WatchedEvent watchedEvent) { if (watchedEvent.getType() == Event.EventType.NodeChildrenChanged) { registry(); } } } }
负载均衡之轮询算法
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 package com.java.roundrrobin;import java.util.Iterator;import java.util.List; * @auth zhengzhi.ren * @date 2015/7/27. * round robin algorithm of load balance */ public class RoundRobin <T > { private List<T> collection; public RoundRobin (List<T> collection) { this .collection = collection; } public Iterator<T> iterator () { return new Iterator<T>() { private int index = 0 ; @Override public boolean hasNext () { return false ; } @Override public T next () { if (collection == null || collection.size() <= 0 ){ return null ; } T e = collection.get(index); index = (index + 1 ) % collection.size(); return e; } @Override public void remove () { throw new UnsupportedOperationException(); } }; } public List<T> getCollection () { return collection; } public void setCollection (List<T> collection) { this .collection = collection; } }
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