使用Maven插件构建Spring Boot应用程序镜像

使用Maven插件构建Spring Boot应用程序的Docker镜像。

环境准备

1.Linux系统
2.安装JDK，Maven
3.安装Docker

应用实践

1.在应用程序根目录下添加Dockerfile文件

并在Dockerfile中编辑构建内容：

FROM openjdk:8-jdk-alpine
VOLUME /tmp
ARG JAR_FILE
COPY ${JAR_FILE} app.jar
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]

2.在项目pom.xml中添加docker镜像构建插件dockerfile-maven-plugin

<build>
    <plugins>
        <!-- 使用Maven插件直接将应用打包为一个Docker镜像 -->
        <plugin>
            <groupId>com.spotify</groupId>
            <artifactId>dockerfile-maven-plugin</artifactId>
            <version>1.3.6</version>
            <configuration>
                <repository>${docker.image.prefix}/${project.artifactId}</repository>
                <buildArgs>
                    <JAR_FILE>target/${project.build.finalName}.jar</JAR_FILE>
                </buildArgs>
            </configuration>
        </plugin>
    </plugins>
</build>

显然，在插件dockerfile-maven-plugin中配置了2个参数：

• <repository>：指定镜像仓库信息及镜像名称，如：springio/test-springboot
• <buildArgs>：设置构建参数，该参数可以直接在Dockerfile中使用（但是必须在Dockerfile使用ARG指令声明）

3.执行构建

在Spring Boot应用根目录下执行构建：

mvn install dockerfile:build

将会看到如下构建日志：

...
[INFO] Building Docker context /home/chench/workspace/java/test-springboot
[INFO] 
[INFO] Image will be built as springio/test-springboot:latest
[INFO] 
[INFO] Step 1/5 : FROM openjdk:8-jdk-alpine
[INFO] 
[INFO] Pulling from library/openjdk
[INFO] Image ff3a5c916c92: Pulling fs layer
[INFO] Image 5de5f69f42d7: Pulling fs layer
[INFO] Image fd869c8b9b59: Pulling fs layer
[INFO] Image 5de5f69f42d7: Downloading
[INFO] Image 5de5f69f42d7: Verifying Checksum
[INFO] Image 5de5f69f42d7: Download complete
[INFO] Image ff3a5c916c92: Downloading
[INFO] Image fd869c8b9b59: Downloading
[INFO] Image ff3a5c916c92: Verifying Checksum
[INFO] Image ff3a5c916c92: Download complete
[INFO] Image ff3a5c916c92: Extracting
[INFO] Image ff3a5c916c92: Pull complete
[INFO] Image 5de5f69f42d7: Extracting
[INFO] Image 5de5f69f42d7: Pull complete
[INFO] Image fd869c8b9b59: Verifying Checksum
[INFO] Image fd869c8b9b59: Download complete
[INFO] Image fd869c8b9b59: Extracting
[INFO] Image fd869c8b9b59: Pull complete
[INFO] Digest: sha256:e82316151c501a2a0f73b3089da8dc867816470a464fcb191db9f88c2343ad53
[INFO] Status: Downloaded newer image for openjdk:8-jdk-alpine
[INFO]  ---> 224765a6bdbe
[INFO] Step 2/5 : VOLUME /tmp
[INFO] 
[INFO]  ---> Running in 99fc0b2bbcf7
[INFO] Removing intermediate container 99fc0b2bbcf7
[INFO]  ---> 74c89740c46e
[INFO] Step 3/5 : ARG JAR_FILE
[INFO] 
[INFO]  ---> Running in 54d9bf00c9c6
[INFO] Removing intermediate container 54d9bf00c9c6
[INFO]  ---> 81d324efe92b
[INFO] Step 4/5 : COPY ${JAR_FILE} app.jar
[INFO] 
[INFO]  ---> f11354b41c33
[INFO] Step 5/5 : ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]
[INFO] 
[INFO]  ---> Running in 74d40fc4f99c
[INFO] Removing intermediate container 74d40fc4f99c
[INFO]  ---> fbc5e8d75beb
[INFO] Successfully built fbc5e8d75beb
[INFO] Successfully tagged springio/test-springboot:latest
[INFO] 
[INFO] Detected build of image with id fbc5e8d75beb
[INFO] Building jar: /home/chench/workspace/java/test-springboot/target/test-springboot-0.0.1-dev-docker-info.jar
[INFO] Successfully built springio/test-springboot:latest
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 02:41 min
[INFO] Finished at: 2018-05-07T10:41:05+08:00
[INFO] Final Memory: 47M/132M
[INFO] ------------------------------------------------------------------------

从构建日志中可以很清晰地看到，一开始下载Maven的依赖配置，随后就开始使用Dockerfile中的构建指令定制镜像，并且将项目根路径作为构建上下文。
另外，在项目的target目录下将会生成一个名为docker的目录：

在该docker目录下存在如下几个文件：image-id，image-name，repository，tag，其中保存的就是最新构建出来的镜像信息。

构建完毕之后查看在本地镜像仓库是否存在对应镜像：

$docker image ls
REPOSITORY                 TAG                 IMAGE ID            CREATED             SIZE
springio/test-springboot   latest              fbc5e8d75beb        49 seconds ago      138MB

4.验证镜像是否正确

$docker run --name test-springboot -d -p 8080:8080 springio/test-springboot
438246b5f8e8ed7808b3127ed8fce867cd162f050135369c02f09cb2cdc8d49d
$docker container ps
CONTAINER ID        IMAGE                      COMMAND                  CREATED             STATUS              PORTS                    NAMES
438246b5f8e8        springio/test-springboot   "java -Djava.securit…"   5 seconds ago       Up 4 seconds        0.0.0.0:8080->8080/tcp   test-springboot

而且，还可以直接在docker run命令中传递环境变量设置Spring Boot应用程序的运行环境，如：-e "SPRING_PROFILES_ACTIVE=test"。

$docker run --name test-springboot-env2 -e "SPRING_PROFILES_ACTIVE=test" -p 8080:8080 -d springio/test-springboot

5.将镜像推送到仓库

有2种方式可以实现将构建好的Spring Boot应用程序镜像推送到镜像仓库：
（1）构建完毕之后手动推送

mvn dockerfile:push

（2）配置Maven插件在构建完毕之后自动推送

<!-- 使用Maven插件直接将应用打包为一个Docker镜像 -->
<plugin>
    <groupId>com.spotify</groupId>
    <artifactId>dockerfile-maven-plugin</artifactId>
    <version>1.3.6</version>
    <configuration>
        <repository>${docker.image.prefix}/${project.artifactId}</repository>
        <buildArgs>
            <JAR_FILE>target/${project.build.finalName}.jar</JAR_FILE>
        </buildArgs>
    </configuration>
    <!-- 镜像构建完毕之后自动推送到仓库 -->
    <executions>
        <execution>
            <id>default</id>
            <phase>install</phase>
            <goals>
                <goal>build</goal>
                <goal>push</goal>
            </goals>
        </execution>
    </executions>
</plugin>

注意事项

1.可以使用Maven插件便捷地构建Spring Boot应用程序的Docker镜像，但是最核心的还是如何编写Dockerfile构建脚本。
2.在使用Maven插件构建Spring Boot应用程序镜像时，会使用应用程序根路径作为构建上下文。

【参考】
https://spring.io/guides/gs/spring-boot-docker/