mysql blocked because of many connection errors unblock with mysqladmin flush-hosts

错误原因

同一个IP下错误过多导致无法连接，Java会抛出以下异常

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:906)
at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:831)
at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:456)
at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:246)
at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:197)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1644)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1710)
at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2753)
Caused by: com.mysql.cj.exceptions.CJException: null,  message from server: "Host '172.28.168.186' 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:369)
at com.mysql.cj.protocol.a.NativeProtocol.readServerCapabilities(NativeProtocol.java:495)
at com.mysql.cj.protocol.a.NativeProtocol.beforeHandshake(NativeProtocol.java:381)
at com.mysql.cj.protocol.a.NativeProtocol.connect(NativeProtocol.java:1338)
at com.mysql.cj.NativeSession.connect(NativeSession.java:157)
at com.mysql.cj.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:850)
... 7 common frames omitted

解决方案

解除锁定

登录MySQL

mysql -uroot -p

执行

mysql> flush hosts;

修改异常次数上限

执行以下sql查看次数

show global variables like '%max_connect_errors%';

可以修改为一千次

set global max_connect_errors=1000;