一個本地DNS解析和mysql授權導致的Mysq連接失敗問題(Access denied for user 'loan'@'kfcsdb1' (using password: YES))

web:/home/web/install/tomcat8_sm1/logs> mysql -h10.0.29.205 -u loan -p loan
Enter password: 
ERROR 1045 (28000): Access denied for user 'loan'@'kfcsdb1' (using password: YES)

問題：最近項目中遇到個奇怪問題，同事搭建的web服務中的JDBC連接，只要用主機IP地址，就無法連接，只能通過localhost連接。而同樣的IP地址形式的JDBC連接從遠程主機卻能正常連接。JDBC也正常

原因：因為遠程主機能連接，說明mysql的遠程連接已經打開. 最后排查發現，服務器本機配置了/etc/hosts, 在該文件中，10.0.29.205被DNS系統解釋成主機名kfcsdb1.

而在mysql的權限管理中， kfcsdb1被配置成只能用root登錄。所以導致WEB應用中的loan用戶無法連接。而遠程主機本身沒有配置kfcsdb1主機名， 所以能通過mysql的權限檢查。

解決： 從本地登錄mysql, 將kfcsdb1和10.0.29.205授權給loan用戶， 解決問題

web:/home/web/install/tomcat8_sm1/logs> mysql -hlocalhost -uloan -ploan
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 7667
Server version: 5.4.3-beta-log MySQL Community Server (GPL)

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> use mysql;
Database changed
mysql> select host,user from user;
+-----------+------+
| host      | user |
+-----------+------+
| %         | loan |
| 127.0.0.1 | root |
| kfcsdb1   |      |
| kfcsdb1   | root |
| localhost |      |
| localhost | loan |
| localhost | root |
+-----------+------+
7 rows in set (0.00 sec)

以上紅色就是無法本地通過IP登錄的原因，而localhost是可以的

mysql> GRANT ALL PRIVILEGES ON *.* TO 'loan'@'kfcsdb1' IDENTIFIED BY 'loan' WITH GRANT OPTION;
Query OK, 0 rows affected (0.01 sec)

mysql> select host,user from user;
+-----------+------+
| host      | user |
+-----------+------+
| %         | loan |
| 127.0.0.1 | root |
| kfcsdb1   | loan |
| localhost |      |
| localhost | loan |
| localhost | root |
+-----------+------+
6 rows in set (0.00 sec)

mysql> GRANT ALL PRIVILEGES ON *.* TO 'loan'@'10.0.29.205' IDENTIFIED BY 'loan' WITH GRANT OPTION;
Query OK, 0 rows affected (0.00 sec)

mysql> select host,user from user;
+-------------+------+
| host        | user |
+-------------+------+
| %           | loan |
| 10.0.29.205 | loan |
| 127.0.0.1   | root |
| kfcsdb1     | loan |
| localhost   |      |
| localhost   | loan |
| localhost   | root |
+-------------+------+
7 rows in set (0.00 sec)

授權后，loan用戶也能通過IP從本地連接, WEB應用JDBC連接也能正常了