Problem: After upgrading docker service and restarting docker service, nacos can start normally and the related configuration is still there. However, when starting the code, the server is DOWN now, please try again later!
Check the access_log.2021-09-02.log log as follows: Found app=unknow

0.11.25.205 – – [02/Sep/2021:14:46:30 +0800] “PUT /nacos/v1/ns/instance/beat?app=unknown&namespaceId=41ba0c0d-f13f-48a4-9ebf-7390dac6335c&port=8181&clusterName=DEFAULT&ip=10.11.25.205&serviceName=DEFAULT_GROUP%40%40hb-homepage&encoding=UTF-8 HTTP/1.1” 503 43 37 Nacos-Java-Client:v1.2.1 –
10.1.193.42 – – [02/Sep/2021:14:46:30 +0800] “GET /nacos/v1/cs/configs?dataId=alarm-unified.yml&group=DEFAULT_GROUP HTTP/1.1” 404 22 17 Java/1.8.0_111 –
10.1.193.30 – – [02/Sep/2021:14:46:31 +0800] “PUT /nacos/v1/ns/instance/beat?app=unknown&namespaceId=3a0e1249-fd7c-4fcb-b07f-9c209ce91fce&port=8112&clusterName=DEFAULT&ip=10.1.193.30&serviceName=DEFAULT_GROUP%40%40SFTP&encoding=UTF-8 HTTP/1.1” 503 43 3 Nacos-Java-Client:v1.2.1 –
10.1.193.30 – – [02/Sep/2021:14:46:31 +0800] “PUT /nacos/v1/ns/instance/beat?app=unknown&namespaceId=3a0e1249-fd7c-4fcb-b07f-9c209ce91fce&port=8112&clusterName=DEFAULT&ip=10.1.193.30&serviceName=DEFAULT_GROUP%40%40SFTP&encoding=UTF-8 HTTP/1.1” 503 43 11 Nacos-Java-Client:v1.2.1 –

Reason: The dada file under nacos stores user-defined configuration information. Among them, the protocol folder stores information such as the cache computer Ip. Because of the upgrade of container services, metadata changes, so the program can not start properly
Solution:
Delete the copied protocol folder, restart nacos, OK!