Docker Tutorial with Hello World Example

Docker is a developer tool to package applications along with their runtime environment, so anybody can deploy and run them in any other machine without facing runtime environment conflicts. It is very similar to virtual machine concept (virtualization), where you can get a VM image and run it on any supporting hardware. All internal programs in VM will function as they were packaged originally.

Difference between a VM and a docker image is that docker image does not package whole virtual operating system. It uses the OS resources just like other process in developer’s machine, only application and it’s runtime specific dependencies are packaged (Containerization).

Docker allows users to publish docker images and consume those published by others in repositories like Docker Hub.

In this tutorial, learn to install Docker container in windows, to create docker image and to deploy Docker image(which as one simple spring boot based microservice) in developer machine.

Docker Installation

To install docker on Windows 7 machine, follow the bellow steps:

Choose the appropriate Docker installer for your System

Before starting with the installation process we need to understand the exact Docker version that is suitable for the Windows that you are using. Docker has provided two versions of Windows distribution as bellow

For windows 10 we need to follow this link https://docs.docker.com/docker-for-windows/
For Windows 7, 8 and older versions we need to use Docker Toolbox and here is the official link for that https://docs.docker.com/toolbox/overview/

We will follow the Docker tool box installation steps for this article.

Download Docker installer

We need to first download the Docker toolbox distribution from https://download.docker.com/win/stable/DockerToolbox.exe and we will follow the installation steps in local Workstation.

Enable Hardware Virtualization Technology

In order to Docker toolbox works properly we need to make sure your Windows system supports Hardware Virtualization Technology and that virtualization is enabled. Docker has provided detailed step on this here: https://docs.docker.com/toolbox/toolbox_install_windows/#step-1-check-your-version. If we don’t have this enabled then we need to go to BIOS option and enable Hardware Virtualization. The BIOS is bit different for different models of Computer, so please follow official guideline for enabling that.

Run Docker installer

Once we have the Installer downloaded and we have enabled the Hardware Virtualization, we can start the installer. It’s just like a simple another windows based installation process guided by a installation wizard.

Verify your installation

To verify docker installation, open Docker Quickstart Terminal shortcut from either Desktop or Start menu. Verify that Docker prompt is coming and then need to test few basic commands. Docker prompt and sample docker command will look like below.

Note Down the Docker IP

We need to now note down the Docker IP assigned to this Container. We will access this IP to access the Applications installed inside Docker. To know the IP from the command prompt use command docker-machine ip. Here is the sample output of the command. Please note that this IP will be different for different M/Cs.

docker-machine ip output

Create docker Image

We will first create a spring boot based REST API, add docker specific configuration and then we will create docker image.

Create Spring REST Project

Develop one simple hello world Microservice for testing. We have used spring boot and Maven and Eclipse as IDE. Add a REST endpoints so that once this application is deployed in to Docker, we can test this by accessing the rest endpoint.

package com.example.howtodoinjava.hellodocker;

import java.util.Date;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication

public class HelloDockerApplication {

    public static void main(String[] args) {

        SpringApplication.run(HelloDockerApplication.class, args);

    }

}

@RestController

class HelloDockerRestController {

    @RequestMapping("/hello/{name}")

    public String helloDocker(@PathVariable(value = "name") String name) {

        String response = "Hello " + name + " Response received on : " + new Date();

        System.out.println(response);

        return response;

    }

}

Update resources/application.properties with server port information.

server.port = 9080

Now test this microservice by running the project as spring boot application.

Add Docker Configurations

Now create a file named Dockerfile in the root directory and add the below lines as Docker configurations.

FROM openjdk:8-jdk-alpine

VOLUME /tmp

ADD target/hello-docker-0.0.1-SNAPSHOT.jar hello-docker-app.jar

ENV JAVA_OPTS=""

ENTRYPOINT [ "sh", "-c", "java $JAVA_OPTS -Djava.security.egd=file:/dev/./urandom -jar /hello-docker-app.jar"]

This is used by Docker while creating the image. It is basically declaring the Java runtime information and target distributions. For more details, follow docker builder reference.

Add Maven Docker Plugins

Add two maven plugins in the pom.xml file so that we can use the Docker related maven commands while creating the instance. Those plugins are dockerfile-maven-plugin and maven-dependency-plugin.

We have used the minimal configurations required to build the project.

<plugin>

    <groupId>com.spotify</groupId>

    <artifactId>dockerfile-maven-plugin</artifactId>

    <version>1.3.4</version>

    <configuration>

        <repository>${docker.image.prefix}/${project.artifactId}</repository>

    </configuration>

</plugin>

<plugin>

    <groupId>org.apache.maven.plugins</groupId>

    <artifactId>maven-dependency-plugin</artifactId>

    <executions>

        <execution>

            <id>unpack</id>

            <phase>package</phase>

            <goals>

                <goal>unpack</goal>

            </goals>

            <configuration>

                <artifactItems>

                    <artifactItem>

                        <groupId>${project.groupId}</groupId>

                        <artifactId>${project.artifactId}</artifactId>

                        <version>${project.version}</version>

                    </artifactItem>

                </artifactItems>

            </configuration>

        </execution>

    </executions>

</plugin>

Create Docker Image

Now use maven command mvn clean install dockerfile:build to create docker image.

Here is the last few lines of maven output log where it is building the image.

[INFO] Image will be built as hello-howtodoinjava/hello-docker:latest

[INFO]

[INFO] Step 1/5 : FROM openjdk:8-jdk-alpine

[INFO] Pulling from library/openjdk

[INFO] Digest: sha256:2b1f15e04904dd44a2667a07e34c628ac4b239f92f413b587538f801a0a57c88

[INFO] Status: Image is up to date for openjdk:8-jdk-alpine

[INFO]  ---> 478bf389b75b

[INFO] Step 2/5 : VOLUME /tmp

[INFO]  ---> Using cache

[INFO]  ---> f4f6473b3c25

[INFO] Step 3/5 : ADD target/hello-docker-0.0.1-SNAPSHOT.jar hello-docker-app.jar

[INFO]  ---> ce7491518508

[INFO] Removing intermediate container c74867501651

[INFO] Step 4/5 : ENV JAVA_OPTS ""

[INFO]  ---> Running in f7cd27710bf3

[INFO]  ---> 086226135205

[INFO] Removing intermediate container f7cd27710bf3

[INFO] Step 5/5 : ENTRYPOINT sh -c java $JAVA_OPTS -Djava.security.egd=file:/dev/./urandom -jar /hello-docker-app.jar

[INFO]  ---> Running in 9ef14a442715

[INFO]  ---> bf14919a32e2

[INFO] Removing intermediate container 9ef14a442715

[INFO] Successfully built bf14919a32e2

[INFO] Successfully tagged hello-howtodoinjava/hello-docker:latest

[INFO]

[INFO] Detected build of image with id bf14919a32e2

[INFO] Building jar: F:\Study\Technical Writings\docker\hello-docker\target\hello-docker-0.0.1-SNAPSHOT-docker-info.jar

[INFO] Successfully built hello-howtodoinjava/hello-docker:latest

[INFO] ------------------------------------------------------------------------

[INFO] BUILD SUCCESS

[INFO] ------------------------------------------------------------------------

Deploy and Run Docker Image

So we have created the Docker Image (i.e. hello-docker-0.0.1-SNAPSHOT-docker-info.jar). We also have a installed docker container running in our local machine.

Now, to run the docker image inside installed docker container, we will use below command.

docker run -p 8080:9080 -t hello-howtodoinjava/hello-docker  --name hello-docker-image

Here the option -p 8080:9080 is important. It says that expose port 8080 for internal port 9080. Remember our application is running in port 9080 inside docker image and we will access that in port 8080 from outside Docker container.

Now access the application with URL http://192.168.99.100:8080/hello/sajal. Notice that the browser output is same as output of standalone REST API on localhost.

Stop Docker Container

We can list down all docker containers by command docker ps in the terminal and we can use command docker stop <name>

Summary

We learned to install Docker in Windows OS. We also learned to create a spring boot project with one REST endpoint and build Docker image for it. Then we learned to run the docker image inside docker container and tested REST endpoint inside docker image.

Docker is very cool tool to solve very old developer problem that “it works in my local machine”. Now if something works in your machine, you can surely run that on other machine as well.

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