本文演示了如何用 Docker 构建、运行、发布来一个 Spring Boot 应用。

Docker 简介

Docker 是一个 Linux 容器管理工具包,具备“社交”方面,允许用户发布容器的 image (镜像),并使用别人发布的 image。Docker image 是用于运行容器化进程的方案,在本文中,我们将构建一个简单的 Spring Boot 应用程序。

有关 Docker 的详细介绍,可以移步至 《简述 Docker》

前置条件

用 Maven 构建项目

创建目录结构

项目的目录结构因符合 Maven 的约定。

在 *nix 系统下执行 mkdir -p src/main/java/docker_spring_boot ,生产如下结构 :

└── src
    └── main
        └── java
            └── com
                └── waylau
                    └── docker_spring_boot

创建 pom.xml 文件

<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 http://maven.apache.org/maven-v4_0_0.xsd">

	<modelVersion>4.0.0</modelVersion>

	<groupId>com.waylau</groupId>
	<artifactId>docker-spring-boot</artifactId>
	<packaging>jar</packaging>
	<version>1.0.0</version>
	<name>docker-spring-boot</name>
	<description>Getting started with Spring Boot and Docker</description>
	
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.3.3.RELEASE</version>
        <relativePath/>
    </parent>

	<dependencies>
	    <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
	</dependencies>

	<build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
    <!-- tag::plugin[] -->
			<plugin>
				<groupId>com.spotify</groupId>
				<artifactId>docker-maven-plugin</artifactId>
				<version>0.4.3</version>
				<configuration>
					<imageName>${docker.image.prefix}/${project.artifactId}</imageName>
					<dockerDirectory>src/main/docker</dockerDirectory>
					<resources>
						<resource>
							<targetPath>/</targetPath>
							<directory>${project.build.directory}</directory>
							<include>${project.build.finalName}.jar</include>
						</resource>
					</resources>
				</configuration>
			</plugin>
    <!-- end::plugin[] -->
        </plugins>
	</build>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<docker.image.prefix>waylau</docker.image.prefix>
		<spring.boot.version>1.3.3.RELEASE</spring.boot.version>
	</properties>
</project>


Spring Boot Maven plugin 提供了很多方便的功能:

  • 它收集的类路径上所有 jar 文件,并构建成一个单一的、可运行的“über-jar”,这使得它更方便地执行和传输服务。
  • 它搜索的 public static void main() 方法来标记为可运行的类。
  • 它提供了一个内置的依赖解析器,用于设置版本号以匹配 Spring Boot 的依赖。您可以覆盖任何你想要的版本,但它会默认选择的 Boot 的版本集。

Spotify 的 docker-maven-plugin 插件是用于构建 Maven 的 Docker Image

  • imageName指定了镜像的名字,本例为 waylau/docker-spring-boot
  • dockerDirectory指定 Dockerfile 的位置
  • resources是指那些需要和 Dockerfile 放在一起,在构建镜像时使用的文件,一般应用 jar 包需要纳入。本例,只需一个 jar 文件。

编写 Spring Boot 应用

编写一个简单的 Spring Boot 应用 :

src/main/java/com/waylau/docker_spring_boot/Application.java:

package com.waylau.docker_spring_boot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
 
/**
 * 主应用入口
 * @author <a href="http://waylau.com">waylau.com</a>
 * @date 2016年3月19日
 */
@SpringBootApplication
@RestController
public class Application {

	@RequestMapping("/")
	public String home() {
		return "Hello Docker World."
				+ "<br />Welcome to <a href='http://waylau.com'>waylau.com</a></li>";
	}

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

}

解释下上面的代码:

  • 类用 @SpringBootApplication @RestController 标识,可用 Spring MVC 来处理 Web 请求。
  • @RequestMapping/ 映射到 home() ,并将”Hello Docker World” 文本作为响应。
  • main() 方法使用 Spring Boot 的 SpringApplication.run() 方法来启动应用。

运行程序

使用 Maven

编译:

mvn package

运行:

java -jar target/docker-spring-boot-1.0.0.jar

访问项目

如果程序正确运行,浏览器访问 http://localhost:8080/,可以看到页面 “Hello Docker World.” 字样。

将项目容器化

Docker 使用 Dockerfile 文件格式来指定 image 层,

创建文件 src/main/docker/Dockerfile:

FROM frolvlad/alpine-oraclejdk8:slim
VOLUME /tmp
ADD docker-spring-boot-1.0.0.jar app.jar
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]

解释下这个配置文件:

  • VOLUME 指定了临时文件目录为/tmp。其效果是在主机 /var/lib/docker 目录下创建了一个临时文件,并链接到容器的/tmp。改步骤是可选的,如果涉及到文件系统的应用就很有必要了。/tmp目录用来持久化到 Docker 数据文件夹,因为 Spring Boot 使用的内嵌 Tomcat 容器默认使用/tmp作为工作目录
  • 项目的 jar 文件作为 “app.jar” 添加到容器的
  • ENTRYPOINT 执行项目 app.jar。为了缩短 Tomcat 启动时间,添加一个系统属性指向 “/dev/urandom” 作为 Entropy Source

构建 Docker Image

执行构建成为 docker image:

mvn package docker:build

运行

运行 Docker Image

docker run -p 8080:8080 -t waylau/docker-spring-boot
[[email protected] spring-boot]# docker run -p 8080:8080 -t waylau/docker-spring-boot

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.3.3.RELEASE)

2016-03-20 08:45:51.276  INFO 1 --- [           main] c.waylau.docker_spring_boot.Application  : Starting Application v1.0.0 on 048fb623038f with PID 1 (/app.jar started by root in /)
2016-03-20 08:45:51.289  INFO 1 --- [           main] c.waylau.docker_spring_boot.Application  : No active profile set, falling back to default profiles: default
2016-03-20 08:45:51.722  INFO 1 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot[email protected]669af5fc: startup date [Sun Mar 20 08:45:51 GMT 2016]; root of context hierarchy
2016-03-20 08:45:54.874  INFO 1 --- [           main] o.s.b.f.s.DefaultListableBeanFactory     : Overriding bean definition for bean 'beanNameViewResolver' with a different definition: replacing [Root bean: class [null]; scope=; abstract=false; lazyInit=false; autowireMode=3; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration$WhitelabelErrorViewConfiguration; factoryMethodName=beanNameViewResolver; initMethodName=null; destroyMethodName=(inferred); defined in class path resource [org/springframework/boot/autoconfigure/web/ErrorMvcAutoConfiguration$WhitelabelErrorViewConfiguration.class]] with [Root bean: class [null]; scope=; abstract=false; lazyInit=false; autowireMode=3; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter; factoryMethodName=beanNameViewResolver; initMethodName=null; destroyMethodName=(inferred); defined in class path resource [org/springframework/boot/autoconfigure/web/WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter.class]]
2016-03-20 08:45:57.893  INFO 1 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
2016-03-20 08:45:57.982  INFO 1 --- [           main] o.apache.catalina.core.StandardService   : Starting service Tomcat
2016-03-20 08:45:57.984  INFO 1 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.0.32
2016-03-20 08:45:58.473  INFO 1 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2016-03-20 08:45:58.473  INFO 1 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 6877 ms
2016-03-20 08:45:59.672  INFO 1 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean        : Mapping servlet: 'dispatcherServlet' to [/]
2016-03-20 08:45:59.695  INFO 1 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'characterEncodingFilter' to: [/*]
2016-03-20 08:45:59.701  INFO 1 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2016-03-20 08:45:59.703  INFO 1 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2016-03-20 08:45:59.703  INFO 1 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'requestContextFilter' to: [/*]
2016-03-20 08:46:00.862  INFO 1 --- [           main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot[email protected]669af5fc: startup date [Sun Mar 20 08:45:51 GMT 2016]; root of context hierarchy
2016-03-20 08:46:01.166  INFO 1 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/]}" onto public java.lang.String com.waylau.docker_spring_boot.Application.home()
2016-03-20 08:46:01.189  INFO 1 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2016-03-20 08:46:01.190  INFO 1 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2016-03-20 08:46:01.302  INFO 1 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2016-03-20 08:46:01.302  INFO 1 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2016-03-20 08:46:01.438  INFO 1 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2016-03-20 08:46:01.833  INFO 1 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2016-03-20 08:46:02.332  INFO 1 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
2016-03-20 08:46:02.343  INFO 1 --- [           main] c.waylau.docker_spring_boot.Application  : Started Application in 13.194 seconds (JVM running for 15.828)

访问项目

如果程序正确运行,浏览器访问 http://localhost:8080/,可以看到页面 “Hello Docker World.” 字样。

推送 image 到 Docker Hub

首先,你在 Docker Hub 要有注册账号,且创建了相应的库;

其次,docker 推送前,先要登录,否则报unauthorized: access to the requested resource is not authorized的错误

执行:

docker login

输出为:

[[email protected] spring-boot]# docker login
Username: waylau
Password: 
Email: [email protected]
WARNING: login credentials saved in /root/.docker/config.json
Login Succeeded

执行推送

docker push waylau/docker-spring-boot
[[email protected] spring-boot]# docker push waylau/docker-spring-boot
The push refers to a repository [docker.io/waylau/docker-spring-boot]
751d29eef02e: Layer already exists 
4da3741f39c7: Pushed 
5f70bf18a086: Layer already exists 
7e4d0cb13643: Layer already exists 
8f045733649f: Layer already exists 
latest: digest: sha256:eb4d5308ba1bb27489d808279e74784bda6761b3574f4298d746abba59b35164 size: 9415

镜像加速器

Docker Hub 在国外,有时候拉取 Image 极其缓慢,可以使用国内的镜像来实现加速

阿里云

echo "DOCKER_OPTS=\"--registry-mirror=https://yourlocation.mirror.aliyuncs.com\"" | sudo tee -a /etc/default/docker
sudo service docker restart

其中 https://yourlocation.mirror.aliyuncs.com 是您在阿里云注册后的专属加速器地址:

DaoCloud

sudo echo “DOCKER_OPTS=\”\$DOCKER_OPTS –registry-mirror=http://your-id.m.daocloud.io -d\”” >> /etc/default/docker
sudo service docker restart

其中 http://your-id.m.daocloud.io 是您在 DaoCloud 注册后的专属加速器地址:

源码

获取项目源码, https://github.com/waylau/docker-demos 中的 samples/spring-boot

获取项目镜像, 执行

docker pull waylau/docker-spring-boot

参考引用