【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：

<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>
   <artifactId>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());
           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) No alt text provided for this image