Docker部署的Java项目与MySQL容器连接失败排查求助

问题背景 #

所有部署在Linux虚拟机上：MySQL容器将3306端口映射至主机3307，Java项目容器将8080端口映射至主机8080，两者均可正常运行。但Java项目使用jdbc:mysql://mysql:3307/fakenews?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&serverTimezone=Asia/Shanghai连接MySQL时失败，换成虚拟机IP:3307则可正常连接。两个容器处于同一flora网桥，Java项目容器能够ping通mysql容器。

错误日志 #

10:07:27:498 ERROR 1 --- [reate-375097969] com.alibaba.druid.pool.DruidDataSource   : create connection SQLException, url: jdbc:mysql://mysql:3307/fakenews?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&serverTimezone=Asia/Shanghai, errorCode 0, state 08001

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) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:89) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:63) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:73) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:898) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:823) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:448) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:241) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:198) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1657) ~[druid-1.2.6.jar!/:1.2.6]
        at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1723) ~[druid-1.2.6.jar!/:1.2.6]
        at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2801) ~[druid-1.2.6.jar!/:1.2.6]
Caused by: com.mysql.cj.exceptions.CJCommunicationsException: 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.
        at jdk.internal.reflect.GeneratedConstructorAccessor33.newInstance(Unknown Source) ~[na:na]
        at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:na]
        at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490) ~[na:na]
        at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:167) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:89) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.NativeSession.connect(NativeSession.java:120) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:842) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        ... 7 common frames omitted
Caused by: java.net.UnknownHostException: mysql
        at java.base/java.net.InetAddress$CachedAddresses.get(InetAddress.java:797) ~[na:na]
        at java.base/java.net.InetAddress.getAllByName0(InetAddress.java:1509) ~[na:na]
        at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1368) ~[na:na]
        at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1302) ~[na:na]
        at com.mysql.cj.protocol.StandardSocketFactory.connect(StandardSocketFactory.java:130) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:63) ~[mysql-connector-java-8.0.30.jar!/:8.0.30]
        ... 9 common frames omitted

相关配置与运行信息 #

Java项目Dockerfile #

FROM openjdk:11.0
ENV TZ=Asia/Shanghai
RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
COPY TextAnalyse.jar /app.jar
ENTRYPOINT ["java", "-jar", "/app.jar"]

容器运行状态（docker ps输出） #

CONTAINER ID   IMAGE         PORTS                                                  STATUS             NAMES
5bcdd5eff02f   textanalyse   0.0.0.0:8080->8080/tcp, :::8080->8080/tcp              Up 24 minutes      ta
3f44be91fb18   mysql         33060/tcp, 0.0.0.0:3307->3306/tcp, :::3307->3306/tcp   Up About an hour   mysql
584173fb038f   nginx         0.0.0.0:80->80/tcp, :::80->80/tcp                      Up 44 minutes      nginx

容器连通性测试 #

root@1fce4b851205:/# ping mysql
PING mysql (172.18.0.2) 56(84) bytes of data.
64 bytes from mysql.flora (172.18.0.2): icmp_seq=1 ttl=64 time=3.09 ms
64 bytes from mysql.flora (172.18.0.2): icmp_seq=2 ttl=64 time=0.069 ms
64 bytes from mysql.flora (172.18.0.2): icmp_seq=3 ttl=64 time=0.106 ms
64 bytes from mysql.flora (172.18.0.2): icmp_seq=4 ttl=64 time=1.34 ms
64 bytes from mysql.flora (172.18.0.2): icmp_seq=5 ttl=64 time=0.093 ms
64 bytes from mysql.flora (172.18.0.2): icmp_seq=6 ttl=64 time=0.168 ms
64 bytes from mysql.flora (172.18.0.2): icmp_seq=7 ttl=64 time=0.072 ms

问题原因分析 #

1. 端口使用错误：容器间同一网桥内通信时，应访问MySQL容器内部的3306端口，而非主机映射的3307端口。主机端口映射是为外部（虚拟机主机或其他外部网络）访问容器服务设计的，容器间直接通信走容器自身的服务端口即可。
2. 异常误导性：错误日志中出现UnknownHostException: mysql，但实际ping测试证明mysql主机名可以正常解析，该异常是连接端口失败后触发的连带错误，核心问题是尝试访问mysql容器未开放的3307端口导致连接失败。

解决办法 #

修改JDBC连接URL为：

jdbc:mysql://mysql:3306/fakenews?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&serverTimezone=Asia/Shanghai

确保MySQL容器内部的3306端口正常监听（MySQL默认启用该端口）。

内容的提问来源于stack exchange，提问作者Flora