Eureka - 服務續約和註冊、下線(Server)

續約

續約的時候，調用的是服務端的InstanceResource#renewLease方法。調用的是InstanceRegistry.renew方法。

@PUT
public Response renewLease(
        @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication,
        @QueryParam("overriddenstatus") String overriddenStatus,
        @QueryParam("status") String status,
        @QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) {
    boolean isFromReplicaNode = "true".equals(isReplication);
    boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);

    //其餘略
    return response;
}

InstanceRegistry.renew會發一個EventPublish的續約監聽（代碼略），而後調用PeerAwareInstanceRegistryImpl#renew。PeerAwareInstanceRegistryImpl#renew。會調用AbstractInstanceRegistry#renew，若是成功，會進行節點間的複製。

public boolean renew(final String appName, final String id, final boolean isReplication) {
    if (super.renew(appName, id, isReplication)) {
        replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);
        return true;
    }
    return false;
}

AbstractInstanceRegistry#renew，獲取續約，若是有的話。

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 {
        // 其餘略
        renewsLastMin.increment();
        leaseToRenew.renew();
        return true;
    }
}

Lease#renew，更新lastUpdateTimestamp時間。

public void renew() {
    lastUpdateTimestamp = System.currentTimeMillis() + duration;
}

綜上，續約就是更改lastUpdateTimestamp的時間。

註冊

註冊調用的是server的ApplicationResource#addInstance，他調用InstanceRegistry#register，和上面同樣，這個會發布註冊監聽。

public Response addInstance(InstanceInfo info,
                                @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
    //其餘略
    registry.register(info, "true".equals(isReplication));
    return Response.status(204).build();  // 204 to be backwards compatible
}

InstanceRegistry#register會調用PeerAwareInstanceRegistryImpl#register，實際的註冊是AbstractInstanceRegistry#register方法，這個方法在Eureka - Server服務啓動已經提過了，這裏略。註冊成功後，會進行節點間的複製。

@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);
}

下線

下線調用的是InstanceResource#cancelLease，而後他會調用InstanceRegistry#cancel（代碼略）發佈下線監聽。

@DELETE
public Response cancelLease(
        @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
    //其餘略
    boolean isSuccess = registry.cancel(app.getName(), id,
            "true".equals(isReplication));
    //其餘略
}

InstanceRegistry#cancel調用PeerAwareInstanceRegistryImpl#cancel，下線成功後，會進行節點間的複製。

@Override
public boolean cancel(final String appName, final String id,
                      final boolean isReplication) {
    if (super.cancel(appName, id, isReplication)) {
        replicateToPeers(Action.Cancel, appName, id, null, null, isReplication);

        return true;
    }
    return false;
}

AbstractInstanceRegistry#cancel會調用AbstractInstanceRegistry#internalCancel，這個是核心代碼。這裏會設置取消時間戳，並過時讀寫緩存。

@Override
public boolean cancel(String appName, String id, boolean isReplication) {
    return internalCancel(appName, id, isReplication);
}


protected boolean internalCancel(String appName, String id, boolean isReplication) {
    read.lock();
    try {
        //其餘略
        // 設置取消的時間戳
        leaseToCancel.cancel();
        //其餘略
        // 過時緩存，這裏是讀寫緩存
        invalidateCache(appName, vip, svip);    
        }
    } finally {
        read.unlock();
    }
    // 用於自我保護
    synchronized (lock) {
        if (this.expectedNumberOfClientsSendingRenews > 0) {
            // Since the client wants to cancel it, reduce the number of clients to send renews.
            this.expectedNumberOfClientsSendingRenews = this.expectedNumberOfClientsSendingRenews - 1;
            updateRenewsPerMinThreshold();
        }
    }

    return true;
}

另外，Eureka - Server服務啓動提到了EvictionTask#run，他會清除過時的實例，他也會調用AbstractInstanceRegistry#internalCancel方法，因此讀寫緩存的圖更改成：

bug

咱們看到，續約的時候lastUpdateTimestamp = System.currentTimeMillis() + duration;，判斷是否過時的時候，又加了一個duration，因此他剔除的並非90秒沒有心跳的，而是180秒沒有心跳的。

public boolean isExpired(long additionalLeaseMs) {
    return (evictionTimestamp > 0 || System.currentTimeMillis() > (lastUpdateTimestamp + duration + additionalLeaseMs));
}