问题
Nacos启动后，访问http://localhost:8848/nacos/index.html一直访问不了，查看nacos安装目录下的logs/config-fatal.log日志文件发现连接mysql报错，但是通过客户端连接工具测试mysql连接正常；核心报错如下：
Caused by: com.mysql.cj.exceptions.CJException: null, message from server: "Host '192.168.17.106' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'"
更多详细报错信息如下：
2023-09-07 13:51:35,830 WARN [master-db] master db access error
org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is java.sql.SQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:83)
at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:376)
at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:558)
at com.alibaba.nacos.config.server.service.datasource.ExternalDataSourceServiceImpl$SelectMasterTask.run(ExternalDataSourceServiceImpl.java:245)
at com.alibaba.nacos.config.server.service.datasource.ExternalDataSourceServiceImpl.reload(ExternalDataSourceServiceImpl.java:146)
at com.alibaba.nacos.config.server.service.datasource.ExternalDataSourceServiceImpl.init(ExternalDataSourceServiceImpl.java:114)
at com.alibaba.nacos.config.server.service.datasource.DynamicDataSource.getDataSource(DynamicDataSource.java:55)
at com.alibaba.nacos.config.server.service.repository.extrnal.ExternalHistoryConfigInfoPersistServiceImpl.<init>(ExternalHistoryConfigInfoPersistServiceImpl.java:70)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:211)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:87)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1326)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1232)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1389)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1309)
at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:887)
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:791)
at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:229)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1372)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1222)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1389)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1309)
at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:887)
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:791)
at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:229)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1372)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1222)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1389)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1309)
at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:887)
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:791)
at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:229)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1372)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1222)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:953)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:745)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:420)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:307)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1317)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306)
at com.alibaba.nacos.Nacos.main(Nacos.java:35)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:49)
at org.springframework.boot.loader.Launcher.launch(Launcher.java:108)
at org.springframework.boot.loader.Launcher.launch(Launcher.java:58)
at org.springframework.boot.loader.PropertiesLauncher.main(PropertiesLauncher.java:467)
Caused by: java.sql.SQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:110)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:89)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:63)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:73)
at com.mysql.cj.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:899)
at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:824)
at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:449)
at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:242)
at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:198)
at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:138)
at com.zaxxer.hikari.pool.PoolBase.newConnection(PoolBase.java:354)
at com.zaxxer.hikari.pool.PoolBase.newPoolEntry(PoolBase.java:202)
at com.zaxxer.hikari.pool.HikariPool.createPoolEntry(HikariPool.java:473)
at com.zaxxer.hikari.pool.HikariPool.checkFailFast(HikariPool.java:554)
at com.zaxxer.hikari.pool.HikariPool.<init>(HikariPool.java:115)
at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:112)
at org.springframework.jdbc.datasource.DataSourceUtils.fetchConnection(DataSourceUtils.java:159)
at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:117)
at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:80)
... 81 common frames omitted
Caused by: com.mysql.cj.exceptions.CJException: null, message from server: "Host '192.168.17.106' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'"
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:129)
at com.mysql.cj.protocol.a.NativeProtocol.rejectProtocol(NativeProtocol.java:348)
at com.mysql.cj.protocol.a.NativeProtocol.readServerCapabilities(NativeProtocol.java:479)
at com.mysql.cj.protocol.a.NativeProtocol.beforeHandshake(NativeProtocol.java:362)
at com.mysql.cj.protocol.a.NativeProtocol.connect(NativeProtocol.java:1367)
at com.mysql.cj.NativeSession.connect(NativeSession.java:133)
at com.mysql.cj.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:843)
... 95 common frames omitted
2023-09-07 13:51:35,830 ERROR [master-db] master db not found.
2023-09-07 13:51:40,872 ERROR [db-error] master db 192.168.17.106 down.
2023-09-07 13:51:40,944 WARN isQuickStart:false
2023-09-07 13:51:40,947 ERROR Nacos Server did not start because dumpservice bean construction failure :
java.lang.IllegalStateException: No DataSource set
2023-09-07 13:52:44,560 WARN [master-db] jdbc:mysql://localhost:3306/lamp_nacos?characterEncoding=utf8&connectTimeout=1000&socketTimeout=3000&autoReconnect=true&useUnicode=true&useSSL=false&serverTimezone=UTC
2023-09-07 13:52:44,638 WARN isQuickStart:false分析
mysql客户端工具可以连接，证明mysql配置没问题，mysql是正常启动着的；
nacos连接其他数据库正常，证明nacos也是没有问题的；
但是日志打印此错误：
Caused by: com.mysql.cj.exceptions.CJException: null, message from server: "Host '192.168.17.106' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'"
可能的原因：
1）mysql连接数达到上限，限制了客户端连接访问
2）该主机因为出现了太多的连接错误而被 MySQL 服务器自动阻止
解决方案
1）修改mysql最大连接数，支持更多连接；
2）使用`mysqladmin -u root -p flush-hosts` 命令清除 MySQL 服务器中关于该主机的连接错误记录；
3）加大错误请求次数：
修改mysql配置文件，在[mysqld]下面添加 max_connect_errors=1000，然后重启mysql；
再次启动nacos，发现Nacos启动成功了：
