# 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"]

:exclamation: 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](https://spring.io/guides/topicals/spring-boot-docker) 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](https://github.com/GoogleContainerTools/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](https://hub.docker.com/) 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](https://github.com/GoogleContainerTools/jib/tree/master/jib-maven-plugin#using-docker-hub-registry)
* We will push our container to a registry associated with our Kubernetes cluster
* Login to [https://harbor.workshop.demo.ryanjbaxter.com/](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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