motan笔记-服务治理和高可用

Cluster

Cluster is a service broker，Cluster 是服务的经纪人，motan的服务治理和高可用都是通过它来实现的。

@Spi(scope = Scope.PROTOTYPE)
public interface Cluster<T> extends Caller<T> {

    @Override
    void init();

    void setUrl(URL url);

    void setLoadBalance(LoadBalance<T> loadBalance);

    void setHaStrategy(HaStrategy<T> haStrategy);

    void onRefresh(List<Referer<T>> referers);

    List<Referer<T>> getReferers();

    LoadBalance<T> getLoadBalance();
}

负载均衡策略

通过负载均衡策略，来选择服务的引用实例。

@Spi(scope = Scope.PROTOTYPE)
public interface LoadBalance<T> {

    void onRefresh(List<Referer<T>> referers);

    Referer<T> select(Request request);

    void selectToHolder(Request request, List<Referer<T>> refersHolder);

    void setWeightString(String weightString);

}

支持多种负载均衡策略：

• ActiveWeight ， 低并发优化 负载均衡器
• Random， 随机负载均衡器
• ConfigurableWeight ，权重可配置的负载均衡器
• ConsistentHash ，一致性哈希负载均衡器
• LocalFirst ，本地服务优先
• RoundRobin ，轮询

高可用策略

支持两种容错策略：Failfast(快速失败) 和 Failover(故障转移，故障切换)，实现故障节点自动摘除，自动探测恢复，有效进行服务故障隔离，远离服务卡死及雪崩。
···
@Spi(scope = Scope.PROTOTYPE)
public interface HaStrategy {

void setUrl(URL url);

Response call(Request request, LoadBalance<T> loadBalance);

}
···

Failfast

@SpiMeta(name = "failfast")
public class FailfastHaStrategy<T> extends AbstractHaStrategy<T> {

    @Override
    public Response call(Request request, LoadBalance<T> loadBalance) {
        Referer<T> refer = loadBalance.select(request);
        return refer.call(request);
    }
}

Failover

@SpiMeta(name = "failover")
public class FailoverHaStrategy<T> extends AbstractHaStrategy<T> {

    protected ThreadLocal<List<Referer<T>>> referersHolder = new ThreadLocal<List<Referer<T>>>() {
        @Override
        protected java.util.List<com.weibo.api.motan.rpc.Referer<T>> initialValue() {
            return new ArrayList<Referer<T>>();
        }
    };

    @Override
    public Response call(Request request, LoadBalance<T> loadBalance) {

        List<Referer<T>> referers = selectReferers(request, loadBalance);
        if (referers.isEmpty()) {
            throw new MotanServiceException(String.format("FailoverHaStrategy No referers for request:%s, loadbalance:%s", request,
                    loadBalance));
        }
        URL refUrl = referers.get(0).getUrl();
        // 先使用method的配置
        int tryCount =
                refUrl.getMethodParameter(request.getMethodName(), request.getParamtersDesc(), URLParamType.retries.getName(),
                        URLParamType.retries.getIntValue());
        // 如果有问题，则设置为不重试
        if (tryCount < 0) {
            tryCount = 0;
        }

        for (int i = 0; i <= tryCount; i++) {
            Referer<T> refer = referers.get(i % referers.size());
            try {
                request.setRetries(i);
                return refer.call(request);
            } catch (RuntimeException e) {
                // 对于业务异常，直接抛出
                if (ExceptionUtil.isBizException(e)) {
                    throw e;
                } else if (i >= tryCount) {
                    throw e;
                }
                LoggerUtil.warn(String.format("FailoverHaStrategy Call false for request:%s error=%s", request, e.getMessage()));
            }
        }

        throw new MotanFrameworkException("FailoverHaStrategy.call should not come here!");
    }

    protected List<Referer<T>> selectReferers(Request request, LoadBalance<T> loadBalance) {
        List<Referer<T>> referers = referersHolder.get();
        referers.clear();
        loadBalance.selectToHolder(request, referers);
        return referers;
    }

}