InstanceRegistry
InstanceRegistry是Eureka Server中注册表管理的核心接口。在根据类图可以发现它实现了LookUpService和LeaseManager接口。
LeaseManager主要用于维护实例的注册、续租、下线和清理，而LookupService提供对服务实例进行检索的功能。
实例的居住证Lease
初始化
初始化赋值注册时间和上次更新时间
public Lease(T r, int durationInSecs) {
holder = r;
registrationTimestamp = System.currentTimeMillis();
lastUpdateTimestamp = registrationTimestamp;
duration = (durationInSecs * 1000);
}
服务下线
// 下线实例
public void cancel() {
if (evictionTimestamp <= 0) {
evictionTimestamp = System.currentTimeMillis();
}
}
// 判断是否已经清理
public boolean isExpired() {
return isExpired(0l);
}
// 判断是否已经清理
public boolean isExpired(long additionalLeaseMs) {
// 在cancel中可以发现evictionTimestamp被设置为大于0的清理时时间戳
// additionalLeaseMs
// ① 清理定时任务中入参为0
//
return (evictionTimestamp > 0 || System.currentTimeMillis() > (lastUpdateTimestamp + duration + additionalLeaseMs));
}
Eureka Server服务器用ConcurrentHashMap维护实例注册信息。
// ConcurrentHashMap<应用名, Map<实例id, Lease<实例信息>>>
private final ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>> registry
= new ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>();
租约更新
@PUT
public Response renewLease(
@HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication,
@QueryParam("overriddenstatus") String overriddenStatus,
@QueryParam("status") String status,
@QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) {
// 是否是同步节点来的，避免
boolean isFromReplicaNode = "true".equals(isReplication);
// 进行续租操作
boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);
// Not found in the registry, immediately ask for a register
if (!isSuccess) {
// 续租失败，该实例未注册，返回404
logger.warn("Not Found (Renew): {} - {}", app.getName(), id);
return Response.status(Status.NOT_FOUND).build();
}
// Check if we need to sync based on dirty time stamp, the client
// instance might have changed some value
Response response;
// 防止并发冲突
if (lastDirtyTimestamp != null && serverConfig.shouldSyncWhenTimestampDiffers()) {
response = this.validateDirtyTimestamp(Long.valueOf(lastDirtyTimestamp), isFromReplicaNode);
// Store the overridden status since the validation found out the node that replicates wins
if (response.getStatus() == Response.Status.NOT_FOUND.getStatusCode()
&& (overriddenStatus != null)
&& !(InstanceStatus.UNKNOWN.name().equals(overriddenStatus))
&& isFromReplicaNode) {
registry.storeOverriddenStatusIfRequired(app.getAppName(), id, InstanceStatus.valueOf(overriddenStatus));
}
} else {
// 成功续租
response = Response.ok().build();
}
logger.debug("Found (Renew): {} - {}; reply status={}", app.getName(), id, response.getStatus());
return response;
}
AbstractInstanceRegistry#renew()
对于续租的方法，不想注册一样需要整个实例信息，只需要实例名称和对应的实例id即可完成续租。
public boolean renew(String appName, String id, boolean isReplication) {
RENEW.increment(isReplication);
Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
Lease<InstanceInfo> leaseToRenew = null;
if (gMap != null) {
leaseToRenew = gMap.get(id);
}
if (leaseToRenew == null) {
RENEW_NOT_FOUND.increment(isReplication);
logger.warn("DS: Registry: lease doesn't exist, registering resource: {} - {}", appName, id);
return false;
} else {
// 获取实例信息
InstanceInfo instanceInfo = leaseToRenew.getHolder();
if (instanceInfo != null) {
// touchASGCache(instanceInfo.getASGName());
InstanceStatus overriddenInstanceStatus = this.getOverriddenInstanceStatus(
instanceInfo, leaseToRenew, isReplication);
// 如果得到的服务实例最后状态是UNKNOW，取消续约直接return
if (overriddenInstanceStatus == InstanceStatus.UNKNOWN) {
logger.info("Instance status UNKNOWN possibly due to deleted override for instance {}; re-register required", instanceInfo.getId());
RENEW_NOT_FOUND.increment(isReplication);
return false;
}
// 服务状态不一致。
if (!instanceInfo.getStatus().equals(overriddenInstanceStatus)) {
logger.info(
"The instance status {} is different from overridden instance status {} for instance {}. Hence setting the status to overridden status", instanceInfo.getStatus().name(),
instanceInfo.getOverriddenStatus().name(),
instanceInfo.getId());
instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus);
}
}
// 统计每分钟续租的次数，用于自我保护机制
renewsLastMin.increment();
// 更新上次更新时间
leaseToRenew.renew();
return true;
}
}
Lease#renew()
// 更新上次更新时间
public void renew() {
lastUpdateTimestamp = System.currentTimeMillis() + duration;
}
过期租约清理
在AbstractInstanceRegistry中存在EvictionTask用于定时执行exict(0)来服务剔除，默认为60秒一次。但是如果Eureka Server处于自我保护状态，则无法进行清理操作。在进入自我保护状态后，在Eureka Client处，如果向Eureka Server注册失败，将快速超时并尝试与其他的Eureka Server进行通信。“自我保护机制”的设计大大提高了Eureka的可用性。
public void evict(long additionalLeaseMs) {
logger.debug("Running the evict task");
// 判断是否打开了自我保护机制
// isLeaseExpirationEnabled == true 代表未开启自我保护机制
if (!isLeaseExpirationEnabled()) {
logger.debug("DS: lease expiration is currently disabled.");
return;
}
// 遍历resgistry保存的注册信息，用expiredLeases收集所有过期的实例信息
List<Lease<InstanceInfo>> expiredLeases = new ArrayList<>();
for (Entry<String, Map<String, Lease<InstanceInfo>>> groupEntry : registry.entrySet()) {
// 对每个应用的实例列表判断是否需要清理
Map<String, Lease<InstanceInfo>> leaseMap = groupEntry.getValue();
if (leaseMap != null) {
for (Entry<String, Lease<InstanceInfo>> leaseEntry : leaseMap.entrySet()) {
Lease<InstanceInfo> lease = leaseEntry.getValue();
if (lease.isExpired(additionalLeaseMs) && lease.getHolder() != null) {
expiredLeases.add(lease);
}
}
}
}
// To compensate for GC pauses or drifting local time, we need to use current registry size as a base for
// triggering self-preservation. Without that we would wipe out full registry.
int registrySize = (int) getLocalRegistrySize(); // 获取注册的实例数
int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold()); // 获得阈值 0.85（default）*size
// 计算清理数量限制 evictionLimit =
// 注册实例数 - 注册实例数 * 0.85（default） = 0.15 * 注册实例数
int evictionLimit = registrySize - registrySizeThreshold;
// 在limit和需要清理的数量中取较小值
int toEvict = Math.min(expiredLeases.size(), evictionLimit);
// 存在需要清理的实例，这里使用随机算法进行删除
if (toEvict > 0) {
logger.info("Evicting {} items (expired={}, evictionLimit={})", toEvict, expiredLeases.size(), evictionLimit);
// 用随机算法cancel实例
// 根据前面的保护机制，最大下线Math.min(expiredLeases.size(), evictionLimit)个实例
Random random = new Random(System.currentTimeMillis());
for (int i = 0; i < toEvict; i++) {
// Pick a random item (Knuth shuffle algorithm)
int next = i + random.nextInt(expiredLeases.size() - i);
Collections.swap(expiredLeases, i, next);
Lease<InstanceInfo> lease = expiredLeases.get(i);
String appName = lease.getHolder().getAppName();
String id = lease.getHolder().getId();
EXPIRED.increment();
logger.warn("DS: Registry: expired lease for {}/{}", appName, id);
// !! 注意，服务是逐个清理的
internalCancel(appName, id, false);
}
}
}
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