基於權重的隨機負載均衡路由算法

時間 2019-11-07

原文原文鏈接

樣例

private Map<String,Integer> serverMap = new HashMap<String,Integer>(){{
        put("192.168.1.100",1);
        put("192.168.1.101",1);
        put("192.168.1.102",4);
        put("192.168.1.103",1);
        put("192.168.1.104",1);
        put("192.168.1.105",3);
        put("192.168.1.106",1);
        put("192.168.1.107",2);
        put("192.168.1.108",1);
        put("192.168.1.109",1);
        put("192.168.1.110",1);
    }};

    private List<String> servers = new ArrayList<>(serverMap.keySet());

實現一

public void weightRandom(){
        Set<String> keySet = serverMap.keySet();
        List<String> servers = new ArrayList<String>();
        for(Iterator<String> it = keySet.iterator();it.hasNext();){
            String server = it.next();
            int weight = serverMap.get(server);
            for(int i=0;i<weight;i++){
                servers.add(server);
            }
        }
        String server = null;
        Random random = new Random();
        int idx = random.nextInt(servers.size());
        server = servers.get(idx);
        System.out.println(server);
    }

實現二

public String randomWeight(){
        int length = serverMap.size(); // 總個數
        int totalWeight = 0; // 總權重
        boolean sameWeight = true; // 權重是否都同樣
        for (int i = 0; i < length; i++) {
            int weight = serverMap.get(servers.get(i));
            totalWeight += weight; // 累計總權重
            if (sameWeight && i > 0
                    && weight != serverMap.get(servers.get(i-1))) {
                sameWeight = false; // 計算全部權重是否同樣
            }
        }
        if (totalWeight > 0 && ! sameWeight) {
            // 若是權重不相同且權重大於0則按總權重數隨機
            int offset = ThreadLocalRandom.current().nextInt(totalWeight);
            // 並肯定隨機值落在哪一個片段上
            for (int i = 0; i < length; i++) {
                offset -= serverMap.get(servers.get(i));
                if (offset < 0) {
                    return servers.get(i);
                }
            }
        }
        // 若是權重相同或權重爲0則均等隨機
        return servers.get(ThreadLocalRandom.current().nextInt(length));
    }