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【Azure 应用服务】App Service 无法连接到Azure MySQL服务,报错:com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

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:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="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">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifa
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ctId>demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>demo</name>

<properties>
<java.version>1.8</java.version>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>

<dependencies>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.20</version>
</dependency>
</dependencies>
</project>

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());

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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

 

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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