NacosNamingService中selectOneHealthyInstance的原理及作用是什么

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序

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<String>());
    }

    @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<String>(), subscribe);
    }

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

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

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

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

    @Override
    public Instance selectOneHealthyInstance(String serviceName, String groupName, List<String> 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類似，只不過(guò)它返回的是單個(gè)instance；selectOneHealthyInstance也是先從hostReactor獲取serviceInfo

• 如果subscribe為true，則執(zhí)行hostReactor.getServiceInfo獲取serviceInfo，否則執(zhí)行hostReactor.getServiceInfoDirectlyFromServer獲取serviceInfo

• 獲取到serviceInfo之后，selectOneHealthyInstance通過(guò)Balancer.RandomByWeight.selectHost方法來(lái)選取單個(gè)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<String> UNCONSISTENT_SERVICE_WITH_ADDRESS_SERVER = new CopyOnWriteArrayList<String>();

    public static class RandomByWeight {

        public static List<Instance> selectAll(ServiceInfo serviceInfo) {
            List<Instance> 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<Instance> 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<Instance> hosts) {
        NAMING_LOGGER.debug("entry randomWithWeight");
        if (hosts == null || hosts.size() == 0) {
            NAMING_LOGGER.debug("hosts == null || hosts.size() == 0");
            return null;
        }

        Chooser<String, Instance> vipChooser = new Chooser<String, Instance>("www.taobao.com");

        NAMING_LOGGER.debug("new Chooser");

        List<Pair<Instance>> hostsWithWeight = new ArrayList<Pair<Instance>>();
        for (Instance host : hosts) {
            if (host.isHealthy()) {
                hostsWithWeight.add(new Pair<Instance>(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針對(duì)serviceInfo.getHosts()進(jìn)行了空判斷，空的話會(huì)拋出IllegalStateException

• selectHost方法內(nèi)部調(diào)用了selectAll方法，其最后通過(guò)getHostByRandomWeight來(lái)選取單個(gè)healthy的instance

• getHostByRandomWeight方法首先創(chuàng)建一個(gè)Chooser，然后選取healthy的instance構(gòu)造hostsWithWeight，再通過(guò)vipChooser.refresh(hostsWithWeight)進(jìn)行refresh，最后通過(guò)vipChooser.randomWithWeight()選取單個(gè)healthy的instance

Chooser

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

public class Chooser<K, T> {

    private K uniqueKey;

    private volatile Ref<T> ref;

    public T random() {
        List<T> 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<T> 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<Pair<T>>());
    }

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

    public K getUniqueKey() {
        return uniqueKey;
    }

    public Ref<T> getRef() {
        return ref;
    }

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

    //......
}

• Chooser的refresh方法會(huì)根據(jù)itemsWithWeight創(chuàng)建Ref，然后執(zhí)行Ref的refresh方法；randomWithWeight方法通過(guò)Arrays.binarySearch(ref.weights, random)創(chuàng)建初始index，然后根據(jù)index從ref.items獲取元素

Ref

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

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

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

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

            for (Pair<T> 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<T> 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

小結(jié)

• selectOneHealthyInstance跟selectInstances類似，只不過(guò)它返回的是單個(gè)instance；selectOneHealthyInstance也是先從hostReactor獲取serviceInfo

• 如果subscribe為true，則執(zhí)行hostReactor.getServiceInfo獲取serviceInfo，否則執(zhí)行hostReactor.getServiceInfoDirectlyFromServer獲取serviceInfo

• 獲取到serviceInfo之后，selectOneHealthyInstance通過(guò)Balancer.RandomByWeight.selectHost方法來(lái)選取單個(gè)healthy的instance

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