Eureka 作为注册中心，担任着服务节点的注册以及发现，并提供着动态的管理（坏点摘除，服务检测等）。可以说是整个系统的基础设施。

• 注册列表的数据模型
  
  eureka注册列表数据模型
  
  1、Applications
  com.netflix.discovery.shared.Applications
  注册列表，包含注册到当前注册中心上的所有实例信息，每个注册中心在内存中保持一份数据。在Applications中持有Application的队列

    private static final String STATUS_DELIMITER = "_";
    private String appsHashCode;
    private Long versionDelta;
    @XStreamImplicit
    private final AbstractQueue<Application> applications;
    private final Map<String, Application> appNameApplicationMap;
    private final Map<String, VipIndexSupport> virtualHostNameAppMap;
    private final Map<String, VipIndexSupport> secureVirtualHostNameAppMap;

2、Application
注册到注册中心的服务集群信息，Application可以看做为一组对外提供相同服务的集群列表。在Application包含一组提供相同服务的InstanceInfo集合
package com.netflix.discovery.shared

    private String name;
    @XStreamOmitField
    private volatile boolean isDirty = false;
    @XStreamImplicit
    private final Set<InstanceInfo> instances;
    private final AtomicReference<List<InstanceInfo>> shuffledInstances;
    private final Map<String, InstanceInfo> instancesMap;

3、InstanceInfo
注册列表里的单个服务实例信息，代表系统中提供一项服务的某个节点，里面包含节点的基础信息，以及唯一标识instanceId。
com.netflix.appinfo.InstanceInfo

// The (fixed) instanceId for this instanceInfo. This should be unique within the scope of the appName.
    private volatile String instanceId;

    private volatile String appName;
    @Auto
    private volatile String appGroupName;

    private volatile String ipAddr;

    private static final String SID_DEFAULT = "na";
    @Deprecated
    private volatile String sid = SID_DEFAULT;

    private volatile int port = DEFAULT_PORT;
    private volatile int securePort = DEFAULT_SECURE_PORT;

    @Auto
    private volatile String homePageUrl;
    @Auto
    private volatile String statusPageUrl;
    @Auto
    private volatile String healthCheckUrl;
    @Auto
    private volatile String secureHealthCheckUrl;
    @Auto
    private volatile String vipAddress;
    @Auto
    private volatile String secureVipAddress;
    @XStreamOmitField
    private String statusPageRelativeUrl;
    @XStreamOmitField
    private String statusPageExplicitUrl;
    @XStreamOmitField
    private String healthCheckRelativeUrl;
    @XStreamOmitField
    private String healthCheckSecureExplicitUrl;
    @XStreamOmitField
    private String vipAddressUnresolved;
    @XStreamOmitField
    private String secureVipAddressUnresolved;
    @XStreamOmitField
    private String healthCheckExplicitUrl;
    @Deprecated
    private volatile int countryId = DEFAULT_COUNTRY_ID; // Defaults to US
    private volatile boolean isSecurePortEnabled = false;
    private volatile boolean isUnsecurePortEnabled = true;
    private volatile DataCenterInfo dataCenterInfo;
    private volatile String hostName;
    private volatile InstanceStatus status = InstanceStatus.UP;
    private volatile InstanceStatus overriddenStatus = InstanceStatus.UNKNOWN;
    @XStreamOmitField
    private volatile boolean isInstanceInfoDirty = false;
    private volatile LeaseInfo leaseInfo;
    @Auto
    private volatile Boolean isCoordinatingDiscoveryServer = Boolean.FALSE;
    @XStreamAlias("metadata")
    private volatile Map<String, String> metadata;
    @Auto
    private volatile Long lastUpdatedTimestamp;
    @Auto
    private volatile Long lastDirtyTimestamp;
    @Auto
    private volatile ActionType actionType;
    @Auto
    private volatile String asgName;
    private String version = VERSION_UNKNOWN;

4、DataCenterInfo
服务实例所在的数据中心，默认为MyOwn，为InstanceInfo子属性
package com.netflix.appinfo.DataCenterInfo

@JsonRootName("dataCenterInfo")
@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = As.PROPERTY, property = "@class")
@JsonTypeIdResolver(DataCenterTypeInfoResolver.class)
public interface DataCenterInfo {
    enum Name {Netflix, Amazon, MyOwn}
    Name getName();
}

5、LeaseInfo
服务实例的租约信息，用于对服务做健康检查，续租，过期等服务可用性的管理。为InstanceInfo子属性
package com.netflix.appinf.LeaseInfo

  // Client settings
    private int renewalIntervalInSecs = DEFAULT_LEASE_RENEWAL_INTERVAL;
    private int durationInSecs = DEFAULT_LEASE_DURATION;

    // Server populated
    private long registrationTimestamp;
    private long lastRenewalTimestamp;
    private long evictionTimestamp;
    private long serviceUpTimestamp;