Example of how to deploy Spring Boot using Docker

Here we mainly use spring-boot out of the box, which can generate a standalone program, and the maven plug-in docker-maven-plugin

The main steps here

• Build a simple springboot project
• Add docker-maven-plugin and write dockerfile
• Practice generating docker images

A simple Spring Boot project

Take spring boot 2.0 as an example

Add parament dependency in pom.xml file

 <parent>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-parent</artifactId>
 <version>2.0.0.RELEASE</version>
</parent>

Add web and test dependencies

<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>

Create a Controller with an index() method that returns: Hello Docker!

@RestController
public class Controller {
 
  @RequestMapping("/")
  public String index() {
    return "Hello Docker!";
  }
}

Startup Class

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

After adding, start the project. After successful startup, open the browser: http://localhost:8080/, and the page returns: Hello Docker!, indicating that the Spring Boot project is configured normally.

Add dcoker-maven-plugin

Add the Docker image prefix to the properties node in pom.xml

<properties>
 <docker.image.prefix>springboot</docker.image.prefix>
</properties>

Add the docker build plugin in plugins

<build>
    <plugins>
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
      <plugin>
        <groupId>com.spotify</groupId>
        <artifactId>docker-maven-plugin</artifactId>
        <version>1.0.0</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.finalNmae}.jar</include>
            </resource>
          </resources>
        </configuration>
      </plugin>
    </plugins>
  </build>

Writing a Dockerfile

Create a Dockerfile file in the directory src/main/docker. The Dockerfile file is used to explain how to build the image.

FROM openjdk:8-jdk-alpine
VOLUME /tmp
ADD spring-boot-docker-1.0.jar app.jar
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]
EXPOSE 8080

This Dockerfile is very simple. It builds the JDK basic environment and adds the Spring Boot Jar to the image. Here is a brief description:

• FROM means using the Jdk8 environment as the base image. If the image is not local, it will be downloaded from DockerHub.
• VOLUME, VOLUME points to a /tmp directory. Since Spring Boot uses the built-in Tomcat container, Tomcat uses /tmp as the working directory by default. The effect of this command is: create a temporary file in the host's /var/lib/docker directory and link it to the /tmp directory in the container
• ADD, copy the file and rename it
• ENTRYPOINT, to shorten Tomcat startup time, add the java.security.egd system property to point to /dev/urandom as ENTRYPOINT
• EXPOSE indicates that port 8080 provides services

Generate docekr image

A Docker environment is required to package the Spring Boot project.

Three dependencies are required

• jdk environment
• Maven
• Docker environment

If there is no error when running java -version,mvn -version,docker version , the environment is ready.

Enter the project directory

mvn package -Dmavne.test.skip=true
java -jar target/spring-boot-docker-1.0.jar

If it can run normally, it means there is no problem with the jar package.

Then build the image

mvn docker:build

If build success is displayed, it is successful.

Use docker images to view the built image

Run the image

docker run -p 8080:8080 -t springboot/spring-boot-docker

Then curl http://127.0.0.1:8080 and you can see Hello Docker! is returned, indicating success

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