NacosNamingService中selectOneHealthyInstance的原理及作用是什么

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本文主要研究一下NacosNamingService的selectOneHealthyInstance

NacosNamingService

nacos-1.1.3/client/src/main/java/com/alibaba/nacos/client/naming/NacosNamingService.java

public class NacosNamingService implements NamingService {
    private static final String DEFAULT_PORT = "8080";
    private static final long DEFAULT_HEART_BEAT_INTERVAL = TimeUnit.SECONDS.toMillis(5);

    /**
     * Each Naming instance should have different namespace.
     */
    private String namespace;

    private String endpoint;

    private String serverList;

    private String cacheDir;

    private String logName;

    private HostReactor hostReactor;

    private BeatReactor beatReactor;

    private EventDispatcher eventDispatcher;

    private NamingProxy serverProxy;

    //......

    @Override
    public Instance selectOneHealthyInstance(String serviceName) throws NacosException {
        return selectOneHealthyInstance(serviceName, new ArrayList());
    }

    @Override
    public Instance selectOneHealthyInstance(String serviceName, String groupName) throws NacosException {
        return selectOneHealthyInstance(serviceName, groupName, true);
    }

    @Override
    public Instance selectOneHealthyInstance(String serviceName, boolean subscribe) throws NacosException {
        return selectOneHealthyInstance(serviceName, new ArrayList(), subscribe);
    }

    @Override
    public Instance selectOneHealthyInstance(String serviceName, String groupName, boolean subscribe) throws NacosException {
        return selectOneHealthyInstance(serviceName, groupName, new ArrayList(), subscribe);
    }

    @Override
    public Instance selectOneHealthyInstance(String serviceName, List clusters) throws NacosException {
        return selectOneHealthyInstance(serviceName, clusters, true);
    }

    @Override
    public Instance selectOneHealthyInstance(String serviceName, String groupName, List clusters) throws NacosException {
        return selectOneHealthyInstance(serviceName, groupName, clusters, true);
    }

    @Override
    public Instance selectOneHealthyInstance(String serviceName, List clusters, boolean subscribe)
        throws NacosException {
        return selectOneHealthyInstance(serviceName, Constants.DEFAULT_GROUP, clusters, subscribe);
    }

    @Override
    public Instance selectOneHealthyInstance(String serviceName, String groupName, List clusters, boolean subscribe) throws NacosException {

        if (subscribe) {
            return Balancer.RandomByWeight.selectHost(
                hostReactor.getServiceInfo(NamingUtils.getGroupedName(serviceName, groupName), StringUtils.join(clusters, ",")));
        } else {
            return Balancer.RandomByWeight.selectHost(
                hostReactor.getServiceInfoDirectlyFromServer(NamingUtils.getGroupedName(serviceName, groupName), StringUtils.join(clusters, ",")));
        }
    }

    //......
}

• selectOneHealthyInstance跟selectInstances类似，只不过它返回的是单个instance；selectOneHealthyInstance也是先从hostReactor获取serviceInfo

• 如果subscribe为true，则执行hostReactor.getServiceInfo获取serviceInfo，否则执行hostReactor.getServiceInfoDirectlyFromServer获取serviceInfo

• 获取到serviceInfo之后，selectOneHealthyInstance通过Balancer.RandomByWeight.selectHost方法来选取单个healthy的instance

Balancer

nacos-1.1.3/client/src/main/java/com/alibaba/nacos/client/naming/core/Balancer.java

public class Balancer {

    /**
     * report status to server
     */
    public final static List UNCONSISTENT_SERVICE_WITH_ADDRESS_SERVER = new CopyOnWriteArrayList();

    public static class RandomByWeight {

        public static List selectAll(ServiceInfo serviceInfo) {
            List hosts = serviceInfo.getHosts();

            if (CollectionUtils.isEmpty(hosts)) {
                throw new IllegalStateException("no host to srv for serviceInfo: " + serviceInfo.getName());
            }

            return hosts;
        }

        public static Instance selectHost(ServiceInfo dom) {

            List hosts = selectAll(dom);

            if (CollectionUtils.isEmpty(hosts)) {
                throw new IllegalStateException("no host to srv for service: " + dom.getName());
            }

            return getHostByRandomWeight(hosts);
        }
    }

    /**
     * Return one host from the host list by random-weight.
     *
     * @param hosts The list of the host.
     * @return The random-weight result of the host
     */
    protected static Instance getHostByRandomWeight(List hosts) {
        NAMING_LOGGER.debug("entry randomWithWeight");
        if (hosts == null || hosts.size() == 0) {
            NAMING_LOGGER.debug("hosts == null || hosts.size() == 0");
            return null;
        }

        Chooser vipChooser = new Chooser("www.taobao.com");

        NAMING_LOGGER.debug("new Chooser");

        List> hostsWithWeight = new ArrayList>();
        for (Instance host : hosts) {
            if (host.isHealthy()) {
                hostsWithWeight.add(new Pair(host, host.getWeight()));
            }
        }
        NAMING_LOGGER.debug("for (Host host : hosts)");
        vipChooser.refresh(hostsWithWeight);
        NAMING_LOGGER.debug("vipChooser.refresh");
        return vipChooser.randomWithWeight();
    }
}

• Balancer的RandomByWeight提供了selectAll及selectHost方法；selectAll针对serviceInfo.getHosts()进行了空判断，空的话会抛出IllegalStateException

• selectHost方法内部调用了selectAll方法，其最后通过getHostByRandomWeight来选取单个healthy的instance

• getHostByRandomWeight方法首先创建一个Chooser，然后选取healthy的instance构造hostsWithWeight，再通过vipChooser.refresh(hostsWithWeight)进行refresh，最后通过vipChooser.randomWithWeight()选取单个healthy的instance

Chooser

nacos-1.1.3/client/src/main/java/com/alibaba/nacos/client/naming/utils/Chooser.java

public class Chooser {

    private K uniqueKey;

    private volatile Ref ref;

    public T random() {
        List items = ref.items;
        if (items.size() == 0) {
            return null;
        }
        if (items.size() == 1) {
            return items.get(0);
        }
        return items.get(ThreadLocalRandom.current().nextInt(items.size()));
    }

    public T randomWithWeight() {
        Ref ref = this.ref;
        double random = ThreadLocalRandom.current().nextDouble(0, 1);
        int index = Arrays.binarySearch(ref.weights, random);
        if (index < 0) {
            index = -index - 1;
        } else {
            return ref.items.get(index);
        }

        if (index >= 0 && index < ref.weights.length) {
            if (random < ref.weights[index]) {
                return ref.items.get(index);
            }
        }

        /* This should never happen, but it ensures we will return a correct
         * object in case there is some floating point inequality problem
         * wrt the cumulative probabilities. */
        return ref.items.get(ref.items.size() - 1);
    }

    public Chooser(K uniqueKey) {
        this(uniqueKey, new ArrayList>());
    }

    public Chooser(K uniqueKey, List> pairs) {
        Ref ref = new Ref(pairs);
        ref.refresh();
        this.uniqueKey = uniqueKey;
        this.ref = ref;
    }

    public K getUniqueKey() {
        return uniqueKey;
    }

    public Ref getRef() {
        return ref;
    }

    public void refresh(List> itemsWithWeight) {
        Ref newRef = new Ref(itemsWithWeight);
        newRef.refresh();
        newRef.poller = this.ref.poller.refresh(newRef.items);
        this.ref = newRef;
    }

    //......
}

• Chooser的refresh方法会根据itemsWithWeight创建Ref，然后执行Ref的refresh方法；randomWithWeight方法通过Arrays.binarySearch(ref.weights, random)创建初始index，然后根据index从ref.items获取元素

Ref

nacos-1.1.3/client/src/main/java/com/alibaba/nacos/client/naming/utils/Chooser.java

    public class Ref {
        private List> itemsWithWeight = new ArrayList>();
        private List items = new ArrayList();
        private Poller poller = new GenericPoller(items);
        private double[] weights;

        @SuppressWarnings("unchecked")
        public Ref(List> itemsWithWeight) {
            this.itemsWithWeight = itemsWithWeight;
        }

        public void refresh() {
            Double originWeightSum = (double) 0;

            for (Pair item : itemsWithWeight) {

                double weight = item.weight();
                //ignore item which weight is zero.see test_randomWithWeight_weight0 in ChooserTest
                if (weight <= 0) {
                    continue;
                }

                items.add(item.item());
                if (Double.isInfinite(weight)) {
                    weight = 10000.0D;
                }
                if (Double.isNaN(weight)) {
                    weight = 1.0D;
                }
                originWeightSum += weight;
            }

            double[] exactWeights = new double[items.size()];
            int index = 0;
            for (Pair item : itemsWithWeight) {
                double singleWeight = item.weight();
                //ignore item which weight is zero.see test_randomWithWeight_weight0 in ChooserTest
                if (singleWeight <= 0) {
                    continue;
                }
                exactWeights[index++] = singleWeight / originWeightSum;
            }

            weights = new double[items.size()];
            double randomRange = 0D;
            for (int i = 0; i < index; i++) {
                weights[i] = randomRange + exactWeights[i];
                randomRange += exactWeights[i];
            }

            double doublePrecisionDelta = 0.0001;

            if (index == 0 || (Math.abs(weights[index - 1] - 1) < doublePrecisionDelta)) {
                return;
            }
            throw new IllegalStateException("Cumulative Weight caculate wrong , the sum of probabilities does not equals 1.");
        }

        //......
    }

• Ref的refresh方法主要是初始化items及weights

小结

• selectOneHealthyInstance跟selectInstances类似，只不过它返回的是单个instance；selectOneHealthyInstance也是先从hostReactor获取serviceInfo

• 如果subscribe为true，则执行hostReactor.getServiceInfo获取serviceInfo，否则执行hostReactor.getServiceInfoDirectlyFromServer获取serviceInfo

• 获取到serviceInfo之后，selectOneHealthyInstance通过Balancer.RandomByWeight.selectHost方法来选取单个healthy的instance

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