Tutorial for spring boot with docker not working?

Question

I've followed the official spring boot docker for gradle tutorial, but I can't make it work.

My build.gradle

buildscript {
    repositories {
        mavenCentral()
        maven {
            url "https://plugins.gradle.org/m2/"
        }
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:2.1.6.RELEASE")
        classpath('gradle.plugin.com.palantir.gradle.docker:gradle-docker:0.22.1')
    }
}

group = 'springio'

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'
apply plugin: 'com.palantir.docker'

task unpack(type: Copy) {
    dependsOn bootJar
    from(zipTree(tasks.bootJar.outputs.files.singleFile))
    into("build/dependency")
}
docker {
    name "${project.group}/${bootJar.baseName}"
    copySpec.from(tasks.unpack.outputs).into("dependency")
    buildArgs(['DEPENDENCY': "dependency"])
}

bootJar {
    baseName = 'globalstatus'
}

sourceCompatibility = 1.8
targetCompatibility = 1.8

repositories {
    mavenCentral()
}


dependencies {
    implementation('org.springframework.boot:spring-boot-starter-web')
    testImplementation('org.springframework.boot:spring-boot-starter-test')
}

My Dockerfile

FROM openjdk:8-jdk-alpine
VOLUME /tmp
ARG JAR_FILE
COPY ${JAR_FILE} app.jar
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]

gradlew build gives me a valid and runnable JAR

But if I do gradlew build docker and then start the container I get

Error: Invalid or corrupt jarfile /app.jar

user_8482479 · Answer

The app.jar should be an executable jar file but it is instead a directory. Because the JAR_FILE is not set as build argument the COPY instruction copies the content of the /build/docker directory to the /app.jar directory in the container. You can list it with:

 docker run --entrypoint="ls" springio/globalstatus -la /app.jar

To fix the build you need to change the docker task:

docker {
    name "${project.group}/${bootJar.baseName}"
    files bootJar.outputs
    buildArgs(['JAR_FILE': bootJar.archiveFileName.get()])
}

Explanation: The docker gradle plugin work directory is /build/docker so when the docker image is build file operations are relative to this path.

files copies the output of the bootJar task into the build/docker directory. The buildArgs sets the build argument JAR_FILE to the name of the archive (the spring boot jar file). When the image is build from Dockerfile, the COPY instruction will add the jar file to the root directory of the container.

Tutorial for spring boot with docker not working?

1 Answers