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聊聊nacos的DistroMapper

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本文主要研究一下nacos的DistroMapper

ServerChangeListener

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/cluster/servers/ServerChangeListener.java

public interface ServerChangeListener {

    /**
     * If member list changed, this method is invoked.
     *
     * @param servers servers after change
     */
    void onChangeServerList(List<Server> servers);

    /**
     * If reachable member list changed, this method is invoked.
     *
     * @param healthyServer reachable servers after change
     */
    void onChangeHealthyServerList(List<Server> healthyServer);
}

ServerChangeListener定义了onChangeServerList、onChangeHealthyServerList方法

DistroMapper

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/core/DistroMapper.java

@Component("distroMapper")
public class DistroMapper implements ServerChangeListener {

    private List<String> healthyList = new ArrayList<>();

    public List<String> getHealthyList() {
        return healthyList;
    }

    @Autowired
    private SwitchDomain switchDomain;

    @Autowired
    private ServerListManager serverListManager;

    /**
     * init server list
     */
    @PostConstruct
    public void init() {
        serverListManager.listen(this);
    }

    public boolean responsible(Cluster cluster, Instance instance) {
        return switchDomain.isHealthCheckEnabled(cluster.getServiceName())
            && !cluster.getHealthCheckTask().isCancelled()
            && responsible(cluster.getServiceName())
            && cluster.contains(instance);
    }

    public boolean responsible(String serviceName) {
        if (!switchDomain.isDistroEnabled() || SystemUtils.STANDALONE_MODE) {
            return true;
        }

        if (CollectionUtils.isEmpty(healthyList)) {
            // means distro config is not ready yet
            return false;
        }

        int index = healthyList.indexOf(NetUtils.localServer());
        int lastIndex = healthyList.lastIndexOf(NetUtils.localServer());
        if (lastIndex < 0 || index < 0) {
            return true;
        }

        int target = distroHash(serviceName) % healthyList.size();
        return target >= index && target <= lastIndex;
    }

    public String mapSrv(String serviceName) {
        if (CollectionUtils.isEmpty(healthyList) || !switchDomain.isDistroEnabled()) {
            return NetUtils.localServer();
        }

        try {
            return healthyList.get(distroHash(serviceName) % healthyList.size());
        } catch (Exception e) {
            Loggers.SRV_LOG.warn("distro mapper failed, return localhost: " + NetUtils.localServer(), e);

            return NetUtils.localServer();
        }
    }

    public int distroHash(String serviceName) {
        return Math.abs(serviceName.hashCode() % Integer.MAX_VALUE);
    }

    @Override
    public void onChangeServerList(List<Server> latestMembers) {

    }

    @Override
    public void onChangeHealthyServerList(List<Server> latestReachableMembers) {

        List<String> newHealthyList = new ArrayList<>();
        for (Server server : latestReachableMembers) {
            newHealthyList.add(server.getKey());
        }
        healthyList = newHealthyList;
    }
}

DistroMapper实现了ServerChangeListener接口，其onChangeHealthyServerList方法会更新healthyList
它还提供了responsible方法，该方法在switchDomain.isHealthCheckEnabled以及cluster.getHealthCheckTask()不是cancelled的情况下会执行responsible，该方法会调用distroHash来计算hash值
它还提供了mapSrv方法，也是通过distroHash计算hash然后与healthyList的大小取余，最后返回server的key

小结

ServerChangeListener定义了onChangeServerList、onChangeHealthyServerList方法；DistroMapper实现了ServerChangeListener接口，其onChangeHealthyServerList方法会更新healthyList；DistroMapper还提供了responsible方法及mapSrv方法