Docker构建SBT应用及docker-compose下MySQL主机名解析故障排查

使用以下docker-compose.yml配置，JDBC连接串中使用了服务名clear_mysql，但应用无法解析该主机名。

docker-compose.yml配置 #

version: "3.9"
services:
    clear_api:
        build:
            context: .
            dockerfile: Dockerfile
        ports:
            - "8080:8080"
        restart: "always"
        depends_on:
            - clear_mysql
            - clear_redis
        links:
            - clear_mysql
            - clear_redis
    clear_mysql:
        image: mysql:5.7
        command: --default-authentication-plugin=mysql_native_password
        restart: always
        ports:
            - 3306:3306
        volumes:
            - ./docker/mysql/data:/var/lib/mysql
            - ./scripts/initialize.sql:/docker-entrypoint-initdb.d/init.sql
        environment:
            MYSQL_ROOT_PASSWORD: root
    clear_redis:
        image: "redis"
        restart: unless-stopped
        ports:
            - 6379:6379
        volumes:
            - ./docker/redis_local:/data

使用的JDBC连接串 #

"jdbc:mysql://clear_mysql/cleardb?useSSL=false"

错误信息 #

#0 120.9 [error] Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure
#0 120.9 [error] The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
#0 120.9 [error]        at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
#0 120.9 [error]        at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:78)
#0 120.9 [error]        at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
#0 120.9 [error]        at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
#0 120.9 [error]        at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
#0 120.9 [error]        at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
#0 120.9 [error]        at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105)
#0 120.9 [error]        at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151)
#0 120.9 [error]        at com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:167)
#0 120.9 [error]        at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:89)
#0 120.9 [error]        at com.mysql.cj.NativeSession.connect(NativeSession.java:120)
#0 121.0 [error]        at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:944)
#0 121.0 [error]        at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:814)
#0 121.0 [error]        ... 14 more
#0 121.0 [error] Caused by: java.net.UnknownHostException: clear_mysql: Name does not resolve
#0 121.0 [error]        at java.base/java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
#0 121.0 [error]        at java.base/java.net.InetAddress$PlatformNameService.lookupAllHostAddr(InetAddress.java:932)

更新：Dockerfile内容 #

FROM oarkflow/clear-sbt as api
RUN apk update && apk add --no-cache curl ca-certificates unzip coreutils bash
WORKDIR /api
COPY ./clear-api .
RUN sbt publishLocal

FROM oarkflow/clear-sbt as service
RUN apk update && apk add --no-cache curl ca-certificates unzip coreutils bash
WORKDIR /service
COPY ./clear-service .
COPY --from=api /root/.ivy2/local/com.example/root/.ivy2/localcom.example
RUN sbt "runMain clear.service.Local"

1. 修正Dockerfile的启动命令 #

你的Dockerfile在service阶段用RUN启动应用，这会导致应用在镜像构建过程中就开始运行，而此时构建环境并未加入docker-compose的网络，自然无法解析clear_mysql主机名。

把启动命令改成CMD，让应用在容器启动后再运行：

FROM oarkflow/clear-sbt as api
RUN apk update && apk add --no-cache curl ca-certificates unzip coreutils bash
WORKDIR /api
COPY ./clear-api .
RUN sbt publishLocal

FROM oarkflow/clear-sbt as service
RUN apk update && apk add --no-cache curl ca-certificates unzip coreutils bash
WORKDIR /service
COPY ./clear-service .
COPY --from=api /root/.ivy2/local/com.example/root/.ivy2/localcom.example
# 替换RUN为CMD，确保容器启动时才运行应用
CMD ["sbt", "runMain", "clear.service.Local"]

2. 移除过时的links配置 #

docker-compose 3.x版本中，同一compose文件的服务默认会加入同一个网络，服务名可直接作为主机名解析，links属于过时配置，建议移除避免混淆。

3. 增强服务启动的依赖等待逻辑 #

depends_on仅保证容器启动顺序，但不保证MySQL服务完全就绪。给clear_mysql添加健康检查，让clear_api等MySQL服务可用后再启动：

修改clear_mysql配置：

clear_mysql:
    image: mysql:5.7
    command: --default-authentication-plugin=mysql_native_password
    restart: always
    ports:
        - 3306:3306
    volumes:
        - ./docker/mysql/data:/var/lib/mysql
        - ./scripts/initialize.sql:/docker-entrypoint-initdb.d/init.sql
    environment:
        MYSQL_ROOT_PASSWORD: root
    healthcheck:
        test: ["CMD", "mysqladmin", "ping", "-h", "localhost", "-u", "root", "-proot"]
        interval: 5s
        timeout: 5s
        retries: 5

修改clear_api的depends_on：

depends_on:
    clear_mysql:
        condition: service_healthy
    clear_redis:
        condition: service_started

4. 补全JDBC连接串信息 #

你的连接串缺少端口和用户名密码，补充完整可避免额外连接问题：

"jdbc:mysql://clear_mysql:3306/cleardb?useSSL=false&user=root&password=root"

内容的提问来源于stack exchange，提问作者Sujit Baniya