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What about Docker ?

You may know that Docker is about Containers, so let's start by answering the question :

What is a Docker Container ? by visiting the Docker site.

Building & Deploying manually with Docker

The goal here is to Containerize the Spring Boot Microservice we just created.

Then, we are 100% sure that running that way, it will be fine on ANY system !

Tip

The best way to avoid the famous "But, it is working on my machine !!"

  1. Create the Dockerfile

    • Create the file named Dockerfile in the root directory of your project, containing :

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      FROM java:8
EXPOSE 8080
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} app.jar
ENTRYPOINT ["java","-jar","/app.jar"]

      Info

      Line 1 : Our micro service is already embedding Tomcat. All it needs to run is Java, so the image can be based on Java only.

      Line 2 : We want to expose the port 8080 of tomcat to acces our APIs from outside the container.

      Line 3-5 : They are just about putting the build jar to the root of tomcat server, and run it.

      The entrypoint is usually a bash script, or as here, a simple bash command.

  2. Build the micro service using maven to get the JAR file ready int the target repository: 

    mvn clean package

  3. Build the docker image manually 

    docker build -t <your_docker_id>/yncrea-hellomicro:latest .

    It will generate the docker image for the micro service and make it available in the local docker registry. The image is tagged as following : 

    docker images

REPOSITORY                                     TAG                 IMAGE ID            CREATED             SIZE
<your_docker_id>/yncrea-hellomicro             latest              b13bcef528c5        46 minutes ago      681MB

  4. Run the image using Docker CLI : 

    docker run -p 8080:8080 -t <your_docker_id>/yncrea-hellomicro:latest
    Access your application REST APIs with your browser.

    Example : http://minikube-ip:8080/hello or http://localhost:8080/hello when using Docker Desktop.

    Tip

    To get the IP of your minikube cluster run the command : minikube ip

    💡 You could also set this ip in your hosts file with the name minikube-ip ...

Building automatically with Maven

Automatize the build using Maven Fabric8 plugin :

  1. Find the latest Fabric8 plugin online

    Add the dependency to you pom.

    Solution
    <dependency>
    <groupId>io.fabric8</groupId>
    <artifactId>docker-maven-plugin</artifactId>
    <version>0.33.0</version>
</dependency>

  2. Configure the plugin to build, tag, and push the image to the local docker registry.

    Solution
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        <build>
        <plugins>
            ...
            <plugin>
                <groupId>io.fabric8</groupId>
                <artifactId>docker-maven-plugin</artifactId>
                <configuration>
                    <images>
                        <image>
                            <name>[your_docker_id]/yncrea-hellomicro</name>
                        </image>
                    </images>
                </configuration>
                <executions>
                    <execution>
                        <id>docker-build</id>
                        <phase>pre-integration-test</phase>
                        <goals>
                            <goal>build</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

    Tip

    You can even use the "save" goal of the plugin in a new execution, in order to save the image as a tar file locally.

    All this, during the maven "pre-integration-test" phase 💪 !

  3. Verify.

    Check your newly built image has been pushed to your local registry (by checking the 'created' time):

    docker images

REPOSITORY                                     TAG                 IMAGE ID            CREATED             SIZE
<your_docker_id>/yncrea-hellomicro             latest              b13bcef528c5        10 seconds ago      681MB

Cleanup

Now it is time to delete our docker container otherwise we will pollute the next labs.

List all docker container running 

docker ps

Find the ID of the Docker Container you just created and use the first 3 digits of it to stop it :

docker stop XYZ

You should not see any containers running yncrea-hellomicro image when doing docker ps.
Access your application REST APIs with your browser should NOT WORK anymore.