权重轮询算法

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相信熟悉过Nginx的都知道，Nginx其中有一个功能是负载均衡。

Nginx的负载均衡里可以配置一个服务器列表，如：

upstream detecotr_server {
            #ip_hash;
                #这里指定多个源服务器，ip:端口,80端口的话可写可不写
                server 192.168.154.1:8080 weight=1;# max_fails=2 fails_time=2;
                server 192.168.154.2:8088 weight=2;# max_fail2=2 fails_time=2;
        }

当负载均衡策略为加权轮询，如果的3个请求，则会有1个请求分发到192.168.154.1服务器上，2个请求分发到192.168.154.2服务器上。加权轮询的算法实现以下：

Java实现

 

public class WeightRoundRobin {

    /**上次选择的服务器*/
    private int currentIndex = -1;
    /**当前调度的权值*/
    private int currentWeight = 0;
    /**最大权重*/
    private int maxWeight;
    /**权重的最大公约数*/
    private int gcdWeight;
    /**服务器数*/
    private int serverCount;
    private List servers = new ArrayList();

    public int greaterCommonDivisor(int a, int b){
        BigInteger aBig = new BigInteger(String.valueOf(a));
        BigInteger bBig = new BigInteger(String.valueOf(b));
        return aBig.gcd(bBig).intValue();
    }

    public int greatestCommonDivisor(List servers){
        int divisor = 0;
        for(int index = 0, len = servers.size(); index < len - 1; index++){
            if(index ==0){
                divisor = greaterCommonDivisor(
                            servers.get(index).getWeight(), servers.get(index + 1).getWeight());
            }else{
                divisor = greaterCommonDivisor(divisor, servers.get(index).getWeight());
            }
        }
        return divisor;
    }

    public int greatestWeight(List servers){
        int weight = 0;
        for(Server server : servers){
            if(weight < server.getWeight()){
                weight = server.getWeight();
            }
        }
        return weight;
    }

    /**
    *  算法流程：
    *  假设有一组服务器 S = {S0, S1, …, Sn-1}
    *  有相应的权重，变量currentIndex表示上次选择的服务器
    *  权值currentWeight初始化为0，currentIndex初始化为-1 ，当第一次的时候返回 权值取最大的那个服务器，
    *  通过权重的不断递减 寻找 适合的服务器返回，直到轮询结束，权值返回为0
    */
    public Server getServer(){
        while(true){
            currentIndex = (currentIndex + 1) % serverCount;
            if(currentIndex == 0){
                currentWeight = currentWeight - gcdWeight;
                if(currentWeight <= 0){
                    currentWeight = maxWeight;
                    if(currentWeight == 0){
                        return null;
                    }
                }
            }
            if(servers.get(currentIndex).getWeight() >= currentWeight){
                return servers.get(currentIndex);
            }
        }
    }

    public void init(){
        servers.add(new Server("192.168.1.101", 1));
        servers.add(new Server("192.168.1.102", 2));
        servers.add(new Server("192.168.1.103", 3));
        servers.add(new Server("192.168.1.104", 4));
        servers.add(new Server("192.168.1.105", 5));

        maxWeight = greatestWeight(servers);
        gcdWeight = greatestCommonDivisor(servers);
        serverCount = servers.size();
    }

    public static void main(String[] args){
        WeightRoundRobin weightRoundRobin = new WeightRoundRobin();
        weightRoundRobin.init();

        for(int i = 0; i < 15; i++){
            Server server = weightRoundRobin.getServer();
            System.out.println("server " + server.getIp() + " weight=" + server.getWeight());
        }
    }

}

class Server{
    private String ip;

    private int weight;

    public Server(String ip, int weight) {
        this.ip = ip;
        this.weight = weight;
    }

    public String getIp() {
        return ip;
    }

    public void setIp(String ip) {
        this.ip = ip;
    }

    public int getWeight() {
        return weight;
    }

    public void setWeight(int weight) {
        this.weight = weight;
    }

    @Override
    public boolean equals(Object obj) {
        if(this == obj) return true;

        if(obj instanceof Server){
            Server server = (Server)obj;

            return getIp().equals(server.getIp());
        }
        return false;
    }

    @Override
    public int hashCode() {
        return getIp().hashCode();
    }

}

结果：

server 192.168.1.105 weight=5
server 192.168.1.104 weight=4
server 192.168.1.105 weight=5
server 192.168.1.103 weight=3
server 192.168.1.104 weight=4
server 192.168.1.105 weight=5
server 192.168.1.102 weight=2
server 192.168.1.103 weight=3
server 192.168.1.104 weight=4
server 192.168.1.105 weight=5
server 192.168.1.101 weight=1
server 192.168.1.102 weight=2
server 192.168.1.103 weight=3
server 192.168.1.104 weight=4
server 192.168.1.105 weight=5

 

 

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