聊聊DependenciesBasedLoadBalancer

序

本文主要研究一下DependenciesBasedLoadBalancer

DependenciesBasedLoadBalancer

spring-cloud-zookeeper-discovery-2.1.2.RELEASE-sources.jar!/org/springframework/cloud/zookeeper/discovery/dependency/DependenciesBasedLoadBalancer.java

public class DependenciesBasedLoadBalancer extends DynamicServerListLoadBalancer {

    private static final Log log = LogFactory.getLog(DependenciesBasedLoadBalancer.class);

    private final Map<String, IRule> ruleCache = new ConcurrentHashMap<>();

    private final ZookeeperDependencies zookeeperDependencies;

    public DependenciesBasedLoadBalancer(ZookeeperDependencies zookeeperDependencies,
            ServerList<?> serverList, IClientConfig config, IPing iPing) {
        super(config);
        this.zookeeperDependencies = zookeeperDependencies;
        setServersList(serverList.getInitialListOfServers());
        setPing(iPing);
        setServerListImpl(serverList);
    }

    @Override
    public Server chooseServer(Object key) {
        String keyAsString;
        if ("default".equals(key)) { // this is the default hint, use name instead
            keyAsString = getName();
        }
        else {
            keyAsString = (String) key;
        }
        ZookeeperDependency dependency = this.zookeeperDependencies
                .getDependencyForAlias(keyAsString);
        log.debug(String.format("Current dependencies are [%s]",
                this.zookeeperDependencies));
        if (dependency == null) {
            log.debug(String.format(
                    "No dependency found for alias [%s] - will use the default rule which is [%s]",
                    keyAsString, this.rule));
            return this.rule.choose(key);
        }
        cacheEntryIfMissing(keyAsString, dependency);
        log.debug(String.format(
                "Will try to retrieve dependency for key [%s]. Current cache contents [%s]",
                keyAsString, this.ruleCache));
        updateListOfServers();
        return this.ruleCache.get(keyAsString).choose(key);
    }

    private void cacheEntryIfMissing(String keyAsString, ZookeeperDependency dependency) {
        if (!this.ruleCache.containsKey(keyAsString)) {
            log.debug(String.format("Cache doesn't contain entry for [%s]", keyAsString));
            this.ruleCache.put(keyAsString,
                    chooseRuleForLoadBalancerType(dependency.getLoadBalancerType()));
        }
    }

    private IRule chooseRuleForLoadBalancerType(LoadBalancerType type) {
        switch (type) {
        case ROUND_ROBIN:
            return getRoundRobinRule();
        case RANDOM:
            return getRandomRule();
        case STICKY:
            return getStickyRule();
        default:
            throw new IllegalArgumentException("Unknown load balancer type " + type);
        }
    }

    private RoundRobinRule getRoundRobinRule() {
        return new RoundRobinRule(this);
    }

    private IRule getRandomRule() {
        RandomRule randomRule = new RandomRule();
        randomRule.setLoadBalancer(this);
        return randomRule;
    }

    private IRule getStickyRule() {
        StickyRule stickyRule = new StickyRule(getRoundRobinRule());
        stickyRule.setLoadBalancer(this);
        return stickyRule;
    }

}

• DependenciesBasedLoadBalancer继承了com.netflix.loadbalancer.DynamicServerListLoadBalancer
• 其chooseServer方法会使用zookeeperDependencies.getDependencyForAlias来跟进key获取ZookeeperDependency，如果dependency为null则直接使用rule.choose(key)，不为null则进行chahe，然后更新server列表，最后通过ruleCache.get(keyAsString).choose(key)返回
• cacheEntryIfMissing方法会根据ZookeeperDependency.getLoadBalancerType()进行chooseRuleForLoadBalancerType，这里分为了ROUND_ROBIN、RANDOM、STICKY三种

StickyRule

spring-cloud-zookeeper-discovery-2.1.2.RELEASE-sources.jar!/org/springframework/cloud/zookeeper/discovery/dependency/StickyRule.java

public class StickyRule extends AbstractLoadBalancerRule {

    private static final Log log = LogFactory.getLog(StickyRule.class);

    private final IRule masterStrategy;

    private final AtomicReference<Server> ourInstance = new AtomicReference<>(null);

    private final AtomicInteger instanceNumber = new AtomicInteger(-1);

    public StickyRule(IRule masterStrategy) {
        this.masterStrategy = masterStrategy;
    }

    @Override
    public void initWithNiwsConfig(IClientConfig iClientConfig) {

    }

    @Override
    public Server choose(Object key) {
        final List<Server> instances = getLoadBalancer().getServerList(true);
        log.debug(String.format("Instances taken from load balancer [%s]", instances));
        Server localOurInstance = this.ourInstance.get();
        log.debug(String.format("Current saved instance [%s]", localOurInstance));
        if (!instances.contains(localOurInstance)) {
            this.ourInstance.compareAndSet(localOurInstance, null);
        }
        if (this.ourInstance.get() == null) {
            Server instance = this.masterStrategy.choose(key);
            if (this.ourInstance.compareAndSet(null, instance)) {
                this.instanceNumber.incrementAndGet();
            }
        }
        return this.ourInstance.get();
    }

    /**
     * Each time a new instance is picked, an internal counter is incremented. This way
     * you can track when/if the instance changes. The instance can change when the
     * selected instance is not in the current list of instances returned by the instance
     * provider
     * @return instance number
     */
    public int getInstanceNumber() {
        return this.instanceNumber.get();
    }

}

• StickyRule继承了com.netflix.loadbalancer.AbstractLoadBalancerRule；其choose方法首先通过getLoadBalancer().getServerList(true)获取server列表，对于该列表没有localOurInstance的，则更新本地引用为null；然后判断localOurInstance是否为null，为null的话则使用masterStrategy.choose(key)进行选择然后更新；最后返回ourInstance.get()

小结

• DependenciesBasedLoadBalancer继承了com.netflix.loadbalancer.DynamicServerListLoadBalancer
• 其chooseServer方法会使用zookeeperDependencies.getDependencyForAlias来跟进key获取ZookeeperDependency，如果dependency为null则直接使用rule.choose(key)，不为null则进行chahe，然后更新server列表，最后通过ruleCache.get(keyAsString).choose(key)返回
• cacheEntryIfMissing方法会根据ZookeeperDependency.getLoadBalancerType()进行chooseRuleForLoadBalancerType，这里分为了ROUND_ROBIN、RANDOM、STICKY三种

doc

• DependenciesBasedLoadBalancer