Netflix Eureka源码分析（9）——eureka server是如何完成服务注册的

eureka client，启动初始化的时候，有一个组件，叫做InstanceInfoReplicator，服务实例信息复制组件，EurekaClient里面设计一个register()方法就可以了。调用了一个EurekaHttpClient，发送了一个http请求，调用了eureka server的一个restful接口。

我们就是看一下eureka server的restful接口接到了这个请求之后，后面是怎么完成服务实例的注册的。

在这个eureka core的resources包下面，有一堆的resources，这些resource相当于是spring web mvc的controller，用来接收这个http请求的。resources相当于是jersey里面的controller吧。

所有的请求都会发送到eureka server的web应用，最后都会走jersey的servlet，jersey的servlet会根据请求的路径，将请求转发给eureka core里面的resource（相当于是转发给某个controller）。

ApplicationsResource，里面是接收这个请求的。http://localhost:8080/v2/apps/ServiceA，这么一个地址。ServiceA可以认为是一个app name，也可以是app id，标志了一个服务，就是服务名称。用ApplicationResource来处理，这个url发起的是post请求，带着InstanceInfo实例打成的一个json过来的。

（1）ApplicationResource的addInstance()方法，是接收post请求的，看方法名就知道是服务实例的注册的。接收的是一个InstanceInfo，代表了一个服务实例。服务可能会部署在多台机器上，每台机器上部署的就是一个服务实例。

所谓的InstanceInfo，服务实例，里面最主要的就是包含2块数据：

1.主机名、ip地址、端口号、url地址

2.lease（租约）的信息：保持心跳的间隔时间，最近心跳的时间，服务注册的时间，服务启动的时间

@Produces({"application/xml", "application/json"})
public class ApplicationResource {

    @POST
    @Consumes({"application/json", "application/xml"})
    public Response addInstance(InstanceInfo info,
                                @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
        logger.debug("Registering instance {} (replication={})", info.getId(), isReplication);
        // validate that the instanceinfo contains all the necessary required fields
        if (isBlank(info.getId())) {
            return Response.status(400).entity("Missing instanceId").build();
        } else if (isBlank(info.getHostName())) {
            return Response.status(400).entity("Missing hostname").build();
        } else if (isBlank(info.getIPAddr())) {
            return Response.status(400).entity("Missing ip address").build();
        } else if (isBlank(info.getAppName())) {
            return Response.status(400).entity("Missing appName").build();
        } else if (!appName.equals(info.getAppName())) {
            return Response.status(400).entity("Mismatched appName, expecting " + appName + " but was " + info.getAppName()).build();
        } else if (info.getDataCenterInfo() == null) {
            return Response.status(400).entity("Missing dataCenterInfo").build();
        } else if (info.getDataCenterInfo().getName() == null) {
            return Response.status(400).entity("Missing dataCenterInfo Name").build();
        }

        // handle cases where clients may be registering with bad DataCenterInfo with missing data
        DataCenterInfo dataCenterInfo = info.getDataCenterInfo();
        if (dataCenterInfo instanceof UniqueIdentifier) {
            String dataCenterInfoId = ((UniqueIdentifier) dataCenterInfo).getId();
            if (isBlank(dataCenterInfoId)) {
                boolean experimental = "true".equalsIgnoreCase(serverConfig.getExperimental("registration.validation.dataCenterInfoId"));
                if (experimental) {
                    String entity = "DataCenterInfo of type " + dataCenterInfo.getClass() + " must contain a valid id";
                    return Response.status(400).entity(entity).build();
                } else if (dataCenterInfo instanceof AmazonInfo) {
                    AmazonInfo amazonInfo = (AmazonInfo) dataCenterInfo;
                    String effectiveId = amazonInfo.get(AmazonInfo.MetaDataKey.instanceId);
                    if (effectiveId == null) {
                        amazonInfo.getMetadata().put(AmazonInfo.MetaDataKey.instanceId.getName(), info.getId());
                    }
                } else {
                    logger.warn("Registering DataCenterInfo of type {} without an appropriate id", dataCenterInfo.getClass());
                }
            }
        }

        registry.register(info, "true".equals(isReplication));
        return Response.status(204).build();  // 204 to be backwards compatible
    }

}

（2）PeerAwareInstanceRegistry：注册表，包含所有的服务实例注册的信息

PeerAwareInstanceRegistry.register()方法，将服务实例往注册表去进行注册，实际上会调用父类AbstractInstanceRegistry的register()方法中去了

@Singleton
public class PeerAwareInstanceRegistryImpl extends AbstractInstanceRegistry implements PeerAwareInstanceRegistry {

    @Override
    public void register(final InstanceInfo info, final boolean isReplication) {
        int leaseDuration = Lease.DEFAULT_DURATION_IN_SECS;
        if (info.getLeaseInfo() != null && info.getLeaseInfo().getDurationInSecs() > 0) {
            leaseDuration = info.getLeaseInfo().getDurationInSecs();
        }
        super.register(info, leaseDuration, isReplication);
        replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
    }

}

（3）真正执行的是调用父类AbstractInstanceRegistry的register()方法

如果是一个服务实例第一次来注册，就很简单，将服务实例信息放到了一个map中去，形成了这样的数据结构：

ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>

这个就是所谓的注册表，核心的数据结构

public abstract class AbstractInstanceRegistry implements InstanceRegistry {

    //注册表的数据结构
    private final ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>> registry
            = new ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>();

    /**
     * Registers a new instance with a given duration.
     *
     * @see com.netflix.eureka.lease.LeaseManager#register(java.lang.Object, int, boolean)
     */
    public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
        try {
            read.lock();
            Map<String, Lease<InstanceInfo>> gMap = registry.get(registrant.getAppName());
            REGISTER.increment(isReplication);
            if (gMap == null) {
                final ConcurrentHashMap<String, Lease<InstanceInfo>> gNewMap = new ConcurrentHashMap<String, Lease<InstanceInfo>>();
                gMap = registry.putIfAbsent(registrant.getAppName(), gNewMap);
                if (gMap == null) {
                    gMap = gNewMap;
                }
            }
            Lease<InstanceInfo> existingLease = gMap.get(registrant.getId());
            // Retain the last dirty timestamp without overwriting it, if there is already a lease
            if (existingLease != null && (existingLease.getHolder() != null)) {
                Long existingLastDirtyTimestamp = existingLease.getHolder().getLastDirtyTimestamp();
                Long registrationLastDirtyTimestamp = registrant.getLastDirtyTimestamp();
                logger.debug("Existing lease found (existing={}, provided={}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);

                // this is a > instead of a >= because if the timestamps are equal, we still take the remote transmitted
                // InstanceInfo instead of the server local copy.
                if (existingLastDirtyTimestamp > registrationLastDirtyTimestamp) {
                    logger.warn("There is an existing lease and the existing lease's dirty timestamp {} is greater" +
                            " than the one that is being registered {}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);
                    logger.warn("Using the existing instanceInfo instead of the new instanceInfo as the registrant");
                    registrant = existingLease.getHolder();
                }
            } else {
                // The lease does not exist and hence it is a new registration
                synchronized (lock) {
                    if (this.expectedNumberOfRenewsPerMin > 0) {
                        // Since the client wants to cancel it, reduce the threshold
                        // (1
                        // for 30 seconds, 2 for a minute)
                        this.expectedNumberOfRenewsPerMin = this.expectedNumberOfRenewsPerMin + 2;
                        this.numberOfRenewsPerMinThreshold =
                                (int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
                    }
                }
                logger.debug("No previous lease information found; it is new registration");
            }
            Lease<InstanceInfo> lease = new Lease<InstanceInfo>(registrant, leaseDuration);
            if (existingLease != null) {
                lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
            }
            gMap.put(registrant.getId(), lease);
            synchronized (recentRegisteredQueue) {
                recentRegisteredQueue.add(new Pair<Long, String>(
                        System.currentTimeMillis(),
                        registrant.getAppName() + "(" + registrant.getId() + ")"));
            }
            // This is where the initial state transfer of overridden status happens
            if (!InstanceStatus.UNKNOWN.equals(registrant.getOverriddenStatus())) {
                logger.debug("Found overridden status {} for instance {}. Checking to see if needs to be add to the "
                                + "overrides", registrant.getOverriddenStatus(), registrant.getId());
                if (!overriddenInstanceStatusMap.containsKey(registrant.getId())) {
                    logger.info("Not found overridden id {} and hence adding it", registrant.getId());
                    overriddenInstanceStatusMap.put(registrant.getId(), registrant.getOverriddenStatus());
                }
            }
            InstanceStatus overriddenStatusFromMap = overriddenInstanceStatusMap.get(registrant.getId());
            if (overriddenStatusFromMap != null) {
                logger.info("Storing overridden status {} from map", overriddenStatusFromMap);
                registrant.setOverriddenStatus(overriddenStatusFromMap);
            }

            // Set the status based on the overridden status rules
            InstanceStatus overriddenInstanceStatus = getOverriddenInstanceStatus(registrant, existingLease, isReplication);
            registrant.setStatusWithoutDirty(overriddenInstanceStatus);

            // If the lease is registered with UP status, set lease service up timestamp
            if (InstanceStatus.UP.equals(registrant.getStatus())) {
                lease.serviceUp();
            }
            registrant.setActionType(ActionType.ADDED);
            recentlyChangedQueue.add(new RecentlyChangedItem(lease));
            registrant.setLastUpdatedTimestamp();
            invalidateCache(registrant.getAppName(), registrant.getVIPAddress(), registrant.getSecureVipAddress());
            logger.info("Registered instance {}/{} with status {} (replication={})",
                    registrant.getAppName(), registrant.getId(), registrant.getStatus(), isReplication);
        } finally {
            read.unlock();
        }
    }
}

总结：

（1）重点理解服务注册表的数据结构，map

（2）重点理解服务注册的本质：就是将服务实例的信息放入一个map中

Netflix Eureka源码分析（9）——eureka server是如何完成服务注册的

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