问题描述
App Service使用jdbc连接MySQL服务,出现大量的 Communications link failure:
com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server
问题分析
最开始出现连接不上的原因,怀疑是MySQL服务的IP地址白名单没有配置正确的App Service 出站IP。但是根据错误提示,发现明显不对,因为如果是IP地址不允许访问,它的错误消息应该是:
Client with IP address '183.2xx.xx.xx' is not allowed to connect to this MySQL server.
所以不应该是MySQL服务器对IP白名单设置的问题。
为了深入找出问题,单独用Java Spring Boot来写一个简单的数据库连接代码,根据MySQL官方的代码:https://docs.azure.cn/zh-cn/mysql/connect-java
POM.XML内容为:
"1.0" encoding="UTF-8"?>"http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> 4.0.0 com.example demo 0.0.1-SNAPSHOT demo 1.8 1.8 1.8 mysql mysql-connector-java 8.0.20
注:这里使用的 mysql-connector-java 依赖版本为 8.0.20
Java Main函数代码:
public static void main(String[] args) { String url = "jdbc:mysql://xxxxxx.mysql.database.chinacloudapi.cn:3306/xxxxxx?useSSL=true&requireSSL=false&characterEncoding=utf8&serverTimezone=UTC"; String username = "xxxxxx@xxxxxx"; String password = "xxxxxxxxxxxx"; try { Connection connection = DriverManager.getConnection(url, username, password); System.out.println(connection.getMetaData().getURL()); connection.close(); System.out.println("connected!"); } catch (SQLException e) { // TODO Auto-generated catch block System.out.println(e.getMessage()); return; // return because nothing can be done w/out a connection } }
同样的数据库连接字符串,运行结果正常。根据验证结果对比,出现 Communications link failure | The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server, 的JDBC版本为 8.0.15, 所以瞬间定位问题原因:客户端jdbc的驱动问题。
根据这一判断,再次检查了MySQL的版本为8.0并且为单实例(Single Server)。而微软的官方文档中提示了 use 8.0.17+ with MySQL 8.0 (https://docs.microsoft.com/en-us/azure/mysql/concepts-compatibility#mysql-drivers)
随后,对mysql-connector jdbc的版本 8.0.17, 8.0.18, 8.0.19 这三个版本进行验证,看是否不会出现 Communications link failure 异常:
8.0.17 Error
8.0.18 Error
8.0.19 Successful
经过以上验证,得出微软官方文档中的 8.0.17+有问题,需要在8.0.19+的驱动版本后才能成功。(一个调查了三天的大坑)
参考资料
将 Java 和 JDBC 与 Azure Database for MySQL 配合使用 : https://docs.azure.cn/zh-cn/mysql/connect-java