在使用nacos读取mysql数据作为配置中心的时候，有时候电脑没电关机，虚拟机没有挂起，nacos就会有时候无法访问，总结原因

1.mysql与nacos的连接出现问题

解决办法，重启mysql、nacos、docker

之后进入docker的nacos中查看logs/start.out 或 logs/nacos.log
确保有日志表明 “Nacos started successfully in cluster mode. use xxx storage”就ok了

一般问题出现会报，这个就是mysql和nacos的连接问题。
 

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:905)
        at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:830)
        at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:455)
        at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:240)
        at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:199)
        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:158)
        at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:116)
        at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:79)
        at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:371)
        at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:523)
        at com.alibaba.nacos.config.server.service.datasource.ExternalDataSourceServiceImpl$SelectMasterTask.run(ExternalDataSourceServiceImpl.java:208)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)