Spring Cloud-Ribbon ILoadBalancer负载均衡器核心源码(四)

Ribbon负载均衡相关类

AbstractloadBalancer

ILoadBalancer的抽象实现类

public abstract class AbstractLoadBalancer implements ILoadBalancer {

    //服务实例分组枚举
    //• ALL: 所有服务实例。
    //• STATUS_UP: 正常服务的实例。
    //• STATUS_NOT_UP: 停止服务的实例。
    public enum ServerGroup{
        ALL,
        STATUS_UP,
        STATUS_NOT_UP
    }
    //再根据负载均衡器选择服务实例时忽略key
    public Server chooseServer() {
        return chooseServer(null);
    }
    //定义了根据分组类型来获取 不同的服务实例的列表。
    public abstract List<Server> getServerList(ServerGroup serverGroup);
    //对象被用来存储负载均衡器中各个 服务实例当前的属性和 统计信息。 这些信息非常有用， 我们可以利用这些信息来观察负载均衡器的运行情
    //况， 同时这些信息也是用来制定负载均衡策略的重要依据。
    public abstract LoadBalancerStats getLoadBalancerStats();
}

BaseloadBalancer

BaseLoadBalancer 类是和ribbon 负载均衡器的基础实现类，在该类中定义了很多关 于负载均衡器相关的基础内容。

public class BaseLoadBalancer extends AbstractLoadBalancer implements PrimeConnectionListener, IClientConfigAware {
    private static Logger logger = LoggerFactory.getLogger(BaseLoadBalancer.class);
    private static final IRule DEFAULT_RULE = new RoundRobinRule();
    private static final BaseLoadBalancer.SerialPingStrategy DEFAULT_PING_STRATEGY = new BaseLoadBalancer.SerialPingStrategy();
    private static final String DEFAULT_NAME = "default";
    private static final String PREFIX = "LoadBalancer_";
    //BaseLoadBalancer服务选择是委托给IRule 这个接口表示负载均衡选择策略
    protected IRule rule;
    //使用IPing检查服务是否有效的执行对象 内部使用线性轮训  默认实现类内部类 SerialPingStrategy
    protected IPingStrategy pingStrategy;
    //用于检查服务是否有效  默认为空需要注入
    protected IPing ping;
    //维护所有服务
    @Monitor(name = "LoadBalancer_AllServerList", type = DataSourceType.INFORMATIONAL)
    protected volatile List<Server> allServerList;
    //维护有效服务
    @Monitor(name = "LoadBalancer_UpServerList", type = DataSourceType.INFORMATIONAL)
    protected volatile List<Server> upServerList;
    ......

    public BaseLoadBalancer() {
        this.rule = DEFAULT_RULE;//默认使用new RoundRobinRule()
        this.pingStrategy = DEFAULT_PING_STRATEGY;
        this.ping = null;
        this.allServerList = Collections.synchronizedList(new ArrayList());
        this.upServerList = Collections.synchronizedList(new ArrayList());
        .....
        this.ping = null;
        this.setRule(DEFAULT_RULE);
        this.setupPingTask();
    }

    //将服务添加到服务清单
    public void addServer(Server newServer) {
        if (newServer != null) {
            try {
                ArrayList<Server> newList = new ArrayList();
                newList.addAll(this.allServerList);
                newList.add(newServer);
                this.setServersList(newList);
            } catch (Exception var3) {
                logger.error("LoadBalancer [{}]: Error adding newServer {}", new Object[]{this.name, newServer.getHost(), var3});
            }
        }

    }

    //将服务添加到服务清单
    public void addServers(List<Server> newServers) {
        if (newServers != null && newServers.size() > 0) {
            try {
                ArrayList<Server> newList = new ArrayList();
                newList.addAll(this.allServerList);
                newList.addAll(newServers);
                this.setServersList(newList);
            } catch (Exception var3) {
                logger.error("LoadBalancer [{}]: Exception while adding Servers", this.name, var3);
            }
        }

    }

    //将服务添加到服务清单
    void addServers(Object[] newServers) {
        if (newServers != null && newServers.length > 0) {
            try {
                ArrayList<Server> newList = new ArrayList();
                newList.addAll(this.allServerList);
                Object[] var3 = newServers;
                int var4 = newServers.length;

                for (int var5 = 0; var5 < var4; ++var5) {
                    Object server = var3[var5];
                    if (server != null) {
                        if (server instanceof String) {
                            server = new Server((String) server);
                        }

                        if (server instanceof Server) {
                            newList.add((Server) server);
                        }
                    }
                }

                this.setServersList(newList);
            } catch (Exception var7) {
                logger.error("LoadBalancer [{}]: Exception while adding Servers", this.name, var7);
            }
        }

    }

    //获得所有服务
    public List<Server> getAllServers() {
        return Collections.unmodifiableList(this.allServerList);
    }

    //根据组获得服务
    public List<Server> getServerList(ServerGroup serverGroup) {
        switch (serverGroup) {
            case ALL:
                return this.allServerList;
            case STATUS_UP:
                return this.upServerList;
            case STATUS_NOT_UP:
                ArrayList<Server> notAvailableServers = new ArrayList(this.allServerList);
                ArrayList<Server> upServers = new ArrayList(this.upServerList);
                notAvailableServers.removeAll(upServers);
                return notAvailableServers;
            default:
                return new ArrayList();
        }
    }

    //根据实例id获得服务
    public Server chooseServer(Object key) {
        if (this.counter == null) {
            this.counter = this.createCounter();
        }
        this.counter.increment();
        if (this.rule == null) {
            return null;
        } else {
            try {
                return this.rule.choose(key);
            } catch (Exception var3) {
                logger.warn("LoadBalancer [{}]:  Error choosing server for key {}", new Object[]{this.name, key, var3});
                return null;
            }
        }
    }

    //标记服务无效
    public void markServerDown(Server server) {
        if (server != null && server.isAlive()) {
            logger.error("LoadBalancer [{}]:  markServerDown called on [{}]", this.name, server.getId());
            server.setAlive(false);
            this.notifyServerStatusChangeListener(Collections.singleton(server));
        }
    }
}

}

DynamicServerlistloadBalancer

继承BaseloadBalancer 是对BaseloadBalancer扩展 实现了再服务运行期间动态更新的能力 还增加通过过滤器 选择性的过滤一些服务的功能

public class DynamicServerListLoadBalancer<T extends Server> extends BaseLoadBalancer {
    private static final Logger LOGGER = LoggerFactory.getLogger(DynamicServerListLoadBalancer.class);

    boolean isSecure = false;
    boolean useTunnel = false;

    // to keep track of modification of server lists
    protected AtomicBoolean serverListUpdateInProgress = new AtomicBoolean(false);

    //用于更新服务清单 由EurekaRibbonClientConfiguration.ribbonServerList 创建DiscoveryEnabledNIWSServerList
    volatile ServerList<T> serverListImpl;
    //从注册中心获取到服务后更新本地服务
    protected volatile ServerListUpdater serverListUpdtater;
    //通过serverListImpl.getUpdatedListOfServers执行更新操作
    protected final ServerListUpdater.UpdateAction updateAction = new ServerListUpdater.UpdateAction() {
        @Override
        public void doUpdate() {
            updateListOfServers();
        }
    };
    public void updateListOfServers() {
        List<T> servers = new ArrayList<T>();
        if (serverListImpl != null) {
            servers = serverListImpl.getUpdatedListOfServers();
            LOGGER.debug("List of Servers for {} obtained from Discovery client: {}",
                    getIdentifier(), servers);

            if (filter != null) {
                servers = filter.getFilteredListOfServers(servers);
                LOGGER.debug("Filtered List of Servers for {} obtained from Discovery client: {}",
                        getIdentifier(), servers);
            }
        }
        updateAllServerList(servers);
    }
}

ServerList<T>

public interface ServerList<T extends Server> {

    //于获取初始化的服务实例 清单，
    public List<T> getInitialListOfServers();
    //用于获取更新的服务实例清单
    public List<T> getUpdatedListOfServers();

}

DiscoveryEnabledNIWSServerList

public class DiscoveryEnabledNIWSServerList extends AbstractServerList<DiscoveryEnabledServer> {

    public List<DiscoveryEnabledServer> getInitialListOfServers() {
        return this.obtainServersViaDiscovery();
    }

    public List<DiscoveryEnabledServer> getUpdatedListOfServers() {
        return this.obtainServersViaDiscovery();
    }

    private List<DiscoveryEnabledServer> obtainServersViaDiscovery() {
        List<DiscoveryEnabledServer> serverList = new ArrayList();
        if (this.eurekaClientProvider != null && this.eurekaClientProvider.get() != null) {
            EurekaClient eurekaClient = (EurekaClient)this.eurekaClientProvider.get();
            if (this.vipAddresses != null) {
                //可以理解为逻辑服务名字 比如PROVIDER
                String[] var3 = this.vipAddresses.split(",");
                int var4 = var3.length;

                for(int var5 = 0; var5 < var4; ++var5) {
                    String vipAddress = var3[var5];
                    //通过EurekaClient从注册中心拉取服务
                    List<InstanceInfo> listOfInstanceInfo = eurekaClient.getInstancesByVipAddress(vipAddress, this.isSecure, this.targetRegion);
                    Iterator var8 = listOfInstanceInfo.iterator();

                    while(var8.hasNext()) {
                        InstanceInfo ii = (InstanceInfo)var8.next();
                        if (ii.getStatus().equals(InstanceStatus.UP)) {
                            if (this.shouldUseOverridePort) {
                                if (logger.isDebugEnabled()) {
                                    logger.debug("Overriding port on client name: " + this.clientName + " to " + this.overridePort);
                                }

                                InstanceInfo copy = new InstanceInfo(ii);
                                if (this.isSecure) {
                                    ii = (new Builder(copy)).setSecurePort(this.overridePort).build();
                                } else {
                                    ii = (new Builder(copy)).setPort(this.overridePort).build();
                                }
                            }

                            DiscoveryEnabledServer des = this.createServer(ii, this.isSecure, this.shouldUseIpAddr);
                            serverList.add(des);
                        }
                    }

                    if (serverList.size() > 0 && this.prioritizeVipAddressBasedServers) {
                        break;
                    }
                }
            }
            //最终返回拉取的服务
            return serverList;
        } else {
            logger.warn("EurekaClient has not been initialized yet, returning an empty list");
            return new ArrayList();
        }
    }

}

ServerListUpdater

public interface ServerListUpdater {
    public interface UpdateAction {
        void doUpdate();
    }
    //启动服务更新器， 传入的UpdadataAction对象为更新操作的具体实现。
    void start(UpdateAction updateAction);

    //停止服务更新器
    void stop();

    ////荻取最近的更新时间戳
    String getLastUpdate();

    //获取上一次更新到现在的时间间隔，单位为毫秒
    long getDurationSinceLastUpdateMs();

    ////荻取错过的更新周期数
    int getNumberMissedCycles();

    ////荻取核心线程数
    int getCoreThreads();
}

PollingServerListUpdater动态更新服务的默认策略 采用定时任务

EurekaNotificationServerListUpdater 也是动态更新服务但是它利用 Eureka 的事件监听器来驱动服务列表的更新操作。

PollingServerListUpdater

public class PollingServerListUpdater implements ServerListUpdater {
    //是DynamicServerListlodBalancer的成员变量传入
    public synchronized void start(final UpdateAction updateAction) {
        if (this.isActive.compareAndSet(false, true)) {
            Runnable wrapperRunnable = new Runnable() {
                public void run() {
                    if (!PollingServerListUpdater.this.isActive.get()) {
                        if (PollingServerListUpdater.this.scheduledFuture != null) {
                            PollingServerListUpdater.this.scheduledFuture.cancel(true);
                        }

                    } else {
                        try {
                            //外部传入拉取服务 调用的DynamicServerListLoadBalancer.updateAction.doUpdate()   这个doupdate里面调用serverListImpl.getUpdatedListOfServers();拉取服务
                            updateAction.doUpdate();
                            PollingServerListUpdater.this.lastUpdated = System.currentTimeMillis();
                        } catch (Exception var2) {
                            PollingServerListUpdater.logger.warn("Failed one update cycle", var2);
                        }

                    }
                }
            };
            //开启定时任务
            this.scheduledFuture = getRefreshExecutor().scheduleWithFixedDelay(wrapperRunnable, this.initialDelayMs, this.refreshIntervalMs, TimeUnit.MILLISECONDS);
        } else {
            logger.info("Already active, no-op");
        }

    }

}

ServerListFilter

DynamicServerlistloadBalancer 最终拉取服务的方法 涉及到一个filter

@VisibleForTesting
    public void updateListOfServers() {
        List<T> servers = new ArrayList<T>();
        if (serverListImpl != null) {
            servers = serverListImpl.getUpdatedListOfServers();
            LOGGER.debug("List of Servers for {} obtained from Discovery client: {}",
                    getIdentifier(), servers);

            if (filter != null) {
                //对应成员变量volatile ServerListFilter<T> filter;
                servers = filter.getFilteredListOfServers(servers);
                LOGGER.debug("Filtered List of Servers for {} obtained from Discovery client: {}",
                        getIdentifier(), servers);
            }
        }
        updateAllServerList(servers);
    }

public interface ServerListFilter<T extends Server> {
    //主要用于实现对服务实例列表的过滤， 通过传入的 服务实例清单， 根据 一 些规则返回过滤后的服务实例清单
    public List<T> getFilteredListOfServers(List<T> servers);
}

AbstractServerListFilter

这是一 个抽象过滤器，在这里定义了过滤时需要 的一个重要依据对象 LoadBalancerStats, LoadBalancerStats保存了负载均衡器的属性和统计信息

public abstract class AbstractServerListFilter<T extends Server> implements ServerListFilter<T> {
    //保存了负载均衡器的属性和统计信息
    private volatile LoadBalancerStats stats;

    public AbstractServerListFilter() {
    }

    public void setLoadBalancerStats(LoadBalancerStats stats) {
        this.stats = stats;
    }

    public LoadBalancerStats getLoadBalancerStats() {
        return this.stats;
    }
}

ZoneAffinityServerListFilter

该过滤器基于 “ 区域感知 (Zone Affinity)" 的方式实现服务实例的过滤， 也就是说， 它会根据提供服务的实例所处的区域 (Zone) 与消费者自身的所处区域 (Zone) 进行比较， 过滤掉那些不是同处 一 个区

域的实例。

public class ZoneAffinityServerListFilter<T extends Server> extends AbstractServerListFilter<T> implements IClientConfigAware {
    private volatile boolean zoneAffinity;
    private volatile boolean zoneExclusive;

    public List<T> getFilteredListOfServers(List<T> servers) {
        if (this.zone != null && (this.zoneAffinity || this.zoneExclusive) && servers != null && servers.size() > 0) {
            //Iterables.filter实现过滤
            List<T> filteredServers = Lists.newArrayList(Iterables.filter(servers, this.zoneAffinityPredicate.getServerOnlyPredicate()));
            //判断是否要启用区域感知功能 调用下面shouldEnableZoneAffinity方法
            if (this.shouldEnableZoneAffinity(filteredServers)) {
                return filteredServers;
            }

            if (this.zoneAffinity) {
                this.overrideCounter.increment();
            }
        }

        return servers;
    }
    private boolean shouldEnableZoneAffinity(List<T> filtered) {
        if (!this.zoneAffinity && !this.zoneExclusive) {
            return false;
        } else if (this.zoneExclusive) {
            return true;
        } else {
            //保存了负载均衡器的相关统计信息
            LoadBalancerStats stats = this.getLoadBalancerStats();
            if (stats == null) {
                return this.zoneAffinity;
            } else {
                logger.debug("Determining if zone affinity should be enabled with given server list: {}", filtered);
                //取这些过滤后的同区域实例的基础指标(包含实例数量、断路器断开数、 活动请求数、 实例平均负载等)，
                ZoneSnapshot snapshot = stats.getZoneSnapshot(filtered);
                double loadPerServer = snapshot.getLoadPerServer();
                int instanceCount = snapshot.getInstanceCount();
                int circuitBreakerTrippedCount = snapshot.getCircuitTrippedCount();
                /**
                 * 当以下其中一个满足就不启用区域感知
                 *  blackOutServerPercentage: 故障实例百分比(断路器断开数/实例数量) >=0.8。
                 *  activeReqeustsPerServer: 实例平均负载 >=0.6 。
                 * availableServers: 可用实例数(实例数量 - 断路器断开数) <2。
                 */
                if ((double)circuitBreakerTrippedCount / (double)instanceCount < this.blackOutServerPercentageThreshold.get() && loadPerServer < this.activeReqeustsPerServerThreshold.get() && instanceCount - circuitBreakerTrippedCount >= this.availableServersThreshold.get()) {
                    return true;
                } else {
                    logger.debug("zoneAffinity is overriden. blackOutServerPercentage: {}, activeReqeustsPerServer: {}, availableServers: {}", new Object[]{(double)circuitBreakerTrippedCount / (double)instanceCount, loadPerServer, instanceCount - circuitBreakerTrippedCount});
                    return false;
                }
            }
        }
    }

}

DefaultNIWSServerListFilter

完全继承ZoneAffinityServerListFilter 是默认的过滤器

public class DefaultNIWSServerListFilter<T extends Server> extends ZoneAffinityServerListFilter<T> {
    public DefaultNIWSServerListFilter() {
    }
}

ServerListSubsetFilter

ZonePreferenceServerListFilter

/**
 * eureka和ribbon整合额默认过滤器
 */
public class ZonePreferenceServerListFilter extends ZoneAffinityServerListFilter<Server> {
    private String zone;
    public List<Server> getFilteredListOfServers(List<Server> servers) {
        //通过父类的区域感知获得所有服务列表
        List<Server> output = super.getFilteredListOfServers(servers);
        //如果消费者配置了zone
        if (this.zone != null && output.size() == servers.size()) {
            List<Server> local = new ArrayList();
            Iterator var4 = output.iterator();

            //遍历服务列表剔除跟消费者配置zone不一致的服务
            while(var4.hasNext()) {

                Server server = (Server)var4.next();
                if (this.zone.equalsIgnoreCase(server.getZone())) {
                    local.add(server);
                }
            }

            if (!local.isEmpty()) {
                return local;
            }
        }

        return output;
    }
}

ZoneAwareLoadBalancer

public class ZoneAwareLoadBalancer<T extends Server> extends DynamicServerListLoadBalancer<T> {

    //重写了父类的方法
    protected void setServerListForZones(Map<String, List<Server>> zoneServersMap) {
        //父类会获获得所有服务 并根据zone进行分组 每个zone对应一个Zonestats
        super.setServerListForZones(zoneServersMap);
        //创建一个自己的ConcurrentHashMap 存储对应zone的负载均衡器
        if (this.balancers == null) {
            this.balancers = new ConcurrentHashMap();
        }
         //获得服务的迭代器
        Iterator var2 = zoneServersMap.entrySet().iterator();

        Entry existingLBEntry;
        while(var2.hasNext()) {
            existingLBEntry = (Entry)var2.next();
            String zone = ((String)existingLBEntry.getKey()).toLowerCase();
            //内部管理根据balancers 获得对应的负载均衡器(内部会创建对应的IRole规则 没有指定的话 默认Availability­ FilieringRule) 将对应的zone的服务放到对应的负载均衡器
            this.getLoadBalancer(zone).setServersList((List)existingLBEntry.getValue());
        }
        //遍历负载均衡器
        var2 = this.balancers.entrySet().iterator();
        while(var2.hasNext()) {
            existingLBEntry = (Entry)var2.next();
            //检查对应的zone下面是否没有服务了 如果是的话就清空
            if (!zoneServersMap.keySet().contains(existingLBEntry.getKey())) {
                ((BaseLoadBalancer)existingLBEntry.getValue()).setServersList(Collections.emptyList());
            }
        }

    }

    //重写父类的chooseServer
    public Server chooseServer(Object key) {
        //当负载均衡器中的zone大于1的时候才执行自定义策略 否则还是用父类的
        if (ENABLED.get() && this.getLoadBalancerStats().getAvailableZones().size() > 1) {
            Server server = null;

            try {
                LoadBalancerStats lbStats = this.getLoadBalancerStats();
                //为当前负载均衡器的所有zone创建快照
                Map<String, ZoneSnapshot> zoneSnapshot = ZoneAvoidanceRule.createSnapshot(lbStats);
                logger.debug("Zone snapshots: {}", zoneSnapshot);
                if (this.triggeringLoad == null) {
                    this.triggeringLoad = DynamicPropertyFactory.getInstance().getDoubleProperty("ZoneAwareNIWSDiscoveryLoadBalancer." + this.getName() + ".triggeringLoadPerServerThreshold", 0.2D);
                }

                if (this.triggeringBlackoutPercentage == null) {
                    this.triggeringBlackoutPercentage = DynamicPropertyFactory.getInstance().getDoubleProperty("ZoneAwareNIWSDiscoveryLoadBalancer." + this.getName() + ".avoidZoneWithBlackoutPercetage", 0.99999D);
                }
                /**
                 * 对应zone的可用区的选择
                 * . 首先它会剔除符合 这些规则的 Zone区域: 所属实例数为零的 Zone 区域; Zone 区域内实例的平均负载小千零，或者实例故障率( 断路器断开次数/实例数)大 于 等于阙值(默认为0.99999)。
                 * . 然后根据Zone区域的实例平均负载计算出最差的Zone区域，这里的最差指的是 实例平均负载最高的Zone区域。
                 * . 如果在上面的过程中没有符合剔除要求的区域，同时实例最大平均负载小千闾值 (默认为20%), 就直接返回所有Zone区域为可用区域。 否则，从最坏Zone区
                 * 域集合中随机选择 一 个，将它从可用Zone区域集合中 剔除。
                 */
                Set<String> availableZones = ZoneAvoidanceRule.getAvailableZones(zoneSnapshot, this.triggeringLoad.get(), this.triggeringBlackoutPercentage.get());
                logger.debug("Available zones: {}", availableZones);
                //当获取的zone区域不等于空 并且小于总数
                if (availableZones != null && availableZones.size() < zoneSnapshot.keySet().size()) {
                    //随机选择一个
                    String zone = ZoneAvoidanceRule.randomChooseZone(zoneSnapshot, availableZones);
                    logger.debug("Zone chosen: {}", zone);
                    if (zone != null) {
                        BaseLoadBalancer zoneLoadBalancer = this.getLoadBalancer(zone);
                        //选用具体的服务实例  内部使用ZoneAvoidanceRule选择
                        server = zoneLoadBalancer.chooseServer(key);
                    }
                }
            } catch (Exception var8) {
                logger.error("Error choosing server using zone aware logic for load balancer={}", this.name, var8);
            }

            if (server != null) {
                return server;
            } else {
                logger.debug("Zone avoidance logic is not invoked.");
                return super.chooseServer(key);
            }
        } else {
            logger.debug("Zone aware logic disabled or there is only one zone");
            return super.chooseServer(key);
        }
    }

    @VisibleForTesting
    BaseLoadBalancer getLoadBalancer(String zone) {
        zone = zone.toLowerCase();
        BaseLoadBalancer loadBalancer = (BaseLoadBalancer)this.balancers.get(zone);
        if (loadBalancer == null) {
            IRule rule = this.cloneRule(this.getRule());
            loadBalancer = new BaseLoadBalancer(this.getName() + "_" + zone, rule, this.getLoadBalancerStats());
            BaseLoadBalancer prev = (BaseLoadBalancer)this.balancers.putIfAbsent(zone, loadBalancer);
            if (prev != null) {
                loadBalancer = prev;
            }
        }

        return loadBalancer;
    }