一、问题现象
当Nacos重启(大多数情况下是因为重启了机器)，再启动微服务项目的服务时，后端控制台会出现如下异常：
NacosException: failed to req API:/api//nacos/v1/ns/instance after all servers([127.0.0.1:8848]) tried: server is DOWN now, please try again later!
二、解决办法
现有两种解决办法可供参考：
1、如果未做过特殊配置
直接删除(或重命名)protocol文件夹即可
protocol文件夹在安装目录的下列位置：
...\nacos-server-1.4.0\data\
2、如果有特殊配置
修改文件raft_meta、__raft_snapshot_meta中的IP
raft_meta和__raft_snapshot_meta位置如下：
...\nacos-server-1.4.0\data\protocol\raft\naming_persistent_service\meta-data
...\nacos-server-1.4.0\data\protocol\raft\naming_persistent_service\snapshot\snapshot_7（此处可能不是_7，视具体情况而定）
三、注意事项
IP一定要检查仔细，应修改为Nacos所在机器的当前IP。
四、部分异常记录
本异常处理过程中，出现过的部分异常记录如下：
2021-02-21 12:24:04.729 INFO 15344 --- [ restartedMain] com.alibaba.nacos.client.naming : [REGISTER-SERVICE] public registering service DEFAULT_GROUP@@hotbuy-orders with instance: {
"clusterName":"DEFAULT","enabled":true,"ephemeral":true,"healthy":true,"instanceHeartBeatInterval":5000,"instanceHeartBeatTimeOut":15000,"ip":"192.168.0.104","ipDeleteTimeout":30000,"metadata":{
"preserved.register.source":"SPRING_CLOUD"},"port":7000,"weight":1.0}
2021-02-21 12:24:04.754 ERROR 15344 --- [ restartedMain] com.alibaba.nacos.client.naming : request: /nacos/v1/ns/instance failed, servers: [127.0.0.1:8848], code: 503, msg: server is DOWN now, please try again later!
2021-02-21 12:24:04.761 ERROR 15344 --- [ restartedMain] c.a.c.n.registry.NacosServiceRegistry : nacos registry, hotbuy-orders register failed...NacosRegistration{
nacosDiscoveryProperties=NacosDiscoveryProperties{
serverAddr='127.0.0.1:8848', endpoint='', namespace='', watchDelay=30000, logName='', service='hotbuy-orders', weight=1.0, clusterName='DEFAULT', group='DEFAULT_GROUP', namingLoadCacheAtStart='false', metadata={preserved.register.source=SPRING_CLOUD}, registerEnabled=true, ip='192.168.0.104', networkInterface='', port=7000, secure=false, accessKey='', secretKey='', heartBeatInterval=null, heartBeatTimeout=null, ipDeleteTimeout=null}},com.alibaba.nacos.api.exception.NacosException: failed to req API:/api//nacos/v1/ns/instance after all servers([127.0.0.1:8848]) tried: server is DOWN now, please try again later!