Ribbon的AvailabilityFilteringRule

Ribbon的版本是2.3.0.release.

图1

AvailabilityFilteringRule继承了PredicateBasedRule，这是因为使用到了AbstractServerPredicate.

choose方法如下List-1, 轮循选一个，判读是否满足条件，如果满足则返回，超过10次，则调用父类的choose方法选择.

List-1

public Server choose(Object key) {
    int count = 0;

    for(Server server = this.roundRobinRule.choose(key); count++ <= 10; server = this.roundRobinRule.choose(key)) {
        if (this.predicate.apply(new PredicateKey(server))) {
            return server;
        }
    }

    return super.choose(key);
}

来看AvailabilityPredicate，如下List-2, apply方法返回true，需要满足俩个条件，断路器闭合，调用服务的并发请求数小于限制数

List-2

public boolean apply(@Nullable PredicateKey input) {
    LoadBalancerStats stats = this.getLBStats();
    if (stats == null) {
        return true;
    } else {
        return !this.shouldSkipServer(stats.getSingleServerStat(input.getServer()));
    }
}

private boolean shouldSkipServer(ServerStats stats) {
    return CIRCUIT_BREAKER_FILTERING.get() && stats.isCircuitBreakerTripped() || stats.getActiveRequestsCount() >= (Integer)this.activeConnectionsLimit.get();
}

List-1中10次之后还不满足，则调用父类的choose方法，来看下PredicateBasedRule的choose实现，如下List-3

List-3

public Server choose(Object key) {
    ILoadBalancer lb = this.getLoadBalancer();
    Optional<Server> server = this.getPredicate().chooseRoundRobinAfterFiltering(lb.getAllServers(), key);
    return server.isPresent() ? (Server)server.get() : null;
}

chooseRoundRobinAfterFiltering中是如何实现的呢，如下List-4，

获取所有的服务实例
遍历服务列表，过滤掉不满足条件的
在满足条件的服务列表中，再进行RoundRibbon算法，选出服务

List-4

public Optional<Server> chooseRoundRobinAfterFiltering(List<Server> servers, Object loadBalancerKey) {
    List<Server> eligible = this.getEligibleServers(servers, loadBalancerKey);
    return eligible.size() == 0 ? Optional.absent() : Optional.of(eligible.get(this.incrementAndGetModulo(eligible.size())));
}

public List<Server> getEligibleServers(List<Server> servers, Object loadBalancerKey) {
    if (loadBalancerKey == null) {
        return ImmutableList.copyOf(Iterables.filter(servers, this.getServerOnlyPredicate()));
    } else {
        List<Server> results = Lists.newArrayList();
        Iterator var4 = servers.iterator();

        while(var4.hasNext()) {
            Server server = (Server)var4.next();
            if (this.apply(new PredicateKey(loadBalancerKey, server))) {
                results.add(server);
            }
        }
        return results;
    }
}

AvailabilityFilteringRule在RoundRibbon的基础上，选择满足条件的服务，如果10次了还没得到，则在满足条件的服务列表中，再用RoundRibbon算法选择.

Reference

https://github.com/Netflix/ribbon/tree/v2.3.0

来源：https://my.oschina.net/u/2518341/blog/3113982

标签

Ribbon