Other Options For Building Containers

Creating A Dockerfile

• Used to describe how to build a container for your app
• Since Spring Boot just requires Java all you need is a JDK and your jar
• Create a file in the root of your app called Dockerfile with the below content

FROM openjdk:8-jdk-alpine
VOLUME /tmp
COPY target/k8s-demo-app-0.0.1-SNAPSHOT.jar app.jar
ENTRYPOINT ["java","-jar","/app.jar"]

The above is not intended for general purpose production use. It is the quickest, dirtiest way to get a Spring Boot app into a container. See this guide for more detail.

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Choosing A JDK

• JDK 8u192 introduced support for containers
• The JDK will be able to see the memory and CPUs available to the container as opposed to what the host has available

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Building A Container

• To build a container for our app we need to run docker build

$ docker build -t my-dockerfile-k8s-demo ./

• Running docker images will allow you to see the built container

$ docker images
REPOSITORY                            TAG                 IMAGE ID            CREATED             SIZE
my-dockerfile-k8s-demo                latest              ab449be57b9d        5 minutes ago       124MB

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Jib It!

• Jib is a tool from by Google to make building Docker containers easier
• Runs as a Maven or Gradle plugin
• Does not require a Docker deamon
• Implements many Docker best practices automatically
  
  

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Add Jib To Your POM

• Open the POM file of your app and add the following plugin to the build section

...
<build>
   <plugins>
      ...
      <plugin>
          <groupId>com.google.cloud.tools</groupId>
          <artifactId>jib-maven-plugin</artifactId>
          <version>1.8.0</version>
          <configuration>
             <from>
                <image>openjdk:8u222-slim</image>
             </from>
             <to>
                <image>k8s-demo-app</image>
             </to>
             <container>
                <user>nobody:nogroup</user>
             </container>
          </configuration>
       </plugin>
       ...
   </plugins>
</build>
...

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Using Jib To Build A Container

• Now building a container is as simple as building our app

$ ./mvnw clean compile jib:dockerBuild

• NOTE: This still uses your local Docker dameon to build the container

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Putting The Container In A Registry

• Up until this point the container only lives on your machine
• It is useful to instead place the container in a registry
  • Allows others to use the container
• Docker Hub is a popular public registry
• Private registries exist as well

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Using Jib To Push To A Registry

• By default Jib will try and push the image to Docker Hub
• We will push our container to a registry associated with our Kubernetes cluster
• Login to https://harbor.workshop.demo.ryanjbaxter.com/ with your supplied username and password
• Once logged in you will see two projects, one called library and the other with the same name as your user, we will use the one with the same name as your user

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Modify Jib Plugin Configuration

• Back in your POM file, modify the Jib plugin, specifically the image name
  • We also add an execution goal in order to do the container build and push whenever we run our Maven build
• Be sure to replace USERNAME in the image name with your supplied user name

<plugin>
    <groupId>com.google.cloud.tools</groupId>
    <artifactId>jib-maven-plugin</artifactId>
    <version>1.8.0</version>
    <configuration>
        <from>
            <image>openjdk:8u222-slim</image>
        </from>
        <to>
            <image>harbor.workshop.demo.ryanjbaxter.com/[USERNAME]/k8s-demo-app</image>
        </to>
        <container>
            <user>nobody:nogroup</user>
        </container>
    </configuration>
    <executions>
        <execution>
            <phase>package</phase>
            <goals>
                <goal>build</goal>
            </goals>
        </execution>
    </executions>
</plugin>

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