How to generate a docker image of your Spring Boot application

What is Docker?

Docker is a set of platform products as services that uses virtualizations on Operational System level for giving us softwares calleds "containers". The containers are isolated from each other and a group yours softwares, libraries and configuration archives.

Create account Docker Hub
Do docker download on you pc: download

now, with your docker hub account, lets to create a repository!

Well, now we have a public repository

now, do login into the docker hub app, if you use linux, use the command below on terminal:

docker login -u {you_username}, tap enter and write your password.

now, you should to create an archive called "Dockerfile" in root directory, and write those commands:

FROM openjdk:15
VOLUME /tmp
ARG DEPENDENCY=target/dependency
COPY ${DEPENDENCY}/BOOT-INF/lib /app/lib
COPY ${DEPENDENCY}/META-INF /app/META-INF
COPY ${DEPENDENCY}/BOOT-INF/classes /app
ENTRYPOINT ["java","-cp","app:app/lib/*", "com.spiet.aws_spring01.AwsSpring01Application"]

obs: change the com.spiet.Aws... to your package with initialization class

---

Editing build.gradle

First, we need to add the build script, to make build before up the application to image

buildscript {
    ext {
        springBootVersion = '2.5.6'
    }

    repositories {
        mavenCentral()
        maven {
            url "https://plugins.gradle.org/m2/"
        }
    }

    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
        classpath("gradle.plugin.com.palantir.gradle.docker:gradle-docker:0.22.2")
    }
}

obs: see that i need the dependencie palantir.gradle.docker in buildScript, so, in plugin sessons below, we need to add
id 'com.palantir.docker' version '0.22.2' too.

then, below in group:

change the group to your dockerId in docker hub.

NEXT, below, we need to add a bootJar with repository informations and mainClass of application:

bootJar {
    baseName = 'aws_training_01'
    version = '1.0.0'
    mainClassName = "com.pedrospiet.spring01.AwsSpring01Application"
}

---

now, we are going to add the tasks that make our project generated the docker image

task unpack(type: Copy) {
    dependsOn bootJar
    from(zipTree(tasks.bootJar.outputs.files.singleFile))
    into("build/dependency")
}

docker {
    name "${project.group}/${bootJar.baseName}"
    tags "${bootJar.version}"
    copySpec.from(tasks.unpack.outputs).into("dependency")
    buildArgs(['DEPENDENCY': "dependency"])
}

It Works

Running image in a container on Intelij IDEA

First press ALT + 8

click on run

In image session, we can found our image, so click with right button and go to "Create Container"

configure the ports:

go to APPLY and RUN

now we can test in insomnia

IT WORKS!