Error: Invalid or corrupt jarfile /app.jar - docker

Question

I am trying to push a spring boot created microservice to an ibm cloud hosted K8 cluster but am constantly getting the below error on startup:
Error: Invalid or corrupt jarfile /app.jar
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"]
my pom.xml:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>projects</groupId>
<artifactId>mydb2jdbcproject</artifactId>
<version>1</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
<java.version>1.8</java.version>
<spring-cloud.version>Dalston.SR4</spring-cloud.version>
<docker.image.prefix>springio</docker.image.prefix>
<app.name>mydb2jdbcproject</app.name>
</properties>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.15.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<dependency>
<groupId>com.ibm.db2.jcc</groupId>
<artifactId>db2jcc4</artifactId>
<version>4.26.14</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-hystrix</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>javax.json</groupId>
<artifactId>javax.json-api</artifactId>
<version>1.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>com.jayway.jsonpath</groupId>
<artifactId>json-path</artifactId>
<version>2.4.0</version>
</dependency>
<dependency>
<groupId>com.ibm.cloud</groupId>
<artifactId>ibm-cloud-spring-boot-service-bind</artifactId>
<version>1.1.1</version>
</dependency>
<dependency>
<groupId>org.eclipse.microprofile.config</groupId>
<artifactId>microprofile-config-api</artifactId>
<version>1.1</version>
<scope>provided</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<repositories>
<repository>
<id>repo</id>
<url>file://${project.basedir}/lib</url>
</repository>
</repositories>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>com.spotify</groupId>
<artifactId>dockerfile-maven-plugin</artifactId>
<version>1.4.9</version>
<configuration>
<repository>${docker.image.prefix}/${project.artifactId}</repository>
<buildArgs>
<JAR_FILE>target/${project.build.finalName}.jar</JAR_FILE>
</buildArgs>
</configuration>
</plugin>
<plugin>
<groupId>io.fabric8</groupId>
<artifactId>docker-maven-plugin</artifactId>
<extensions>true</extensions>
<configuration>
<images>
<image>
<name>us.icr.io/rbs1/rbstest</name>
<build>
<from>adoptopenjdk/openjdk8-openj9</from>
<entryPoint>
<exec>
<arg>java</arg>
<arg>-jar</arg>
<arg>/${project.build.finalName}.jar</arg>
</exec>
</entryPoint>
<assembly>
<targetDir>/</targetDir>
<mode>dir</mode>
<descriptorRef>artifact</descriptorRef>
</assembly>
</build>
</image>
</images>
</configuration>
</plugin>
</plugins>
</build>
</project>'
my event log:
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 9m10s default-scheduler Successfully assigned default/basic-deployment-768559cfc6-6fd2j to 10.144.195.59
Normal Created 8m15s (x4 over 9m) kubelet, 10.144.195.59 Created container
Normal Started 8m15s (x4 over 9m) kubelet, 10.144.195.59 Started container
Normal Pulling 7m35s (x5 over 9m8s) kubelet, 10.144.195.59 pulling image "------/---------"
Normal Pulled 7m34s (x5 over 9m) kubelet, 10.144.195.59 Successfully pulled image "--------/---------"
Warning BackOff 4m6s (x24 over 8m57s) kubelet, 10.144.195.59 Back-off restarting failed container
The images are held in a docker repository and then pulled into the cluster. I am fully logged in to both docker and ibmcloud. Each time the container restarts 6 times but is always unsuccessful. I run
mvn package
every time before i build the docker image to make sure there is a jar available and the jar is held with in the target folder named mydb2jdbcproject-1.

Answer 1

Rather embarrassingly i hadn't realised that i needed to point towards the right jar file with ${JAR_FILE}. After ensuring it was directed at my app jar it all worked. Thankyou!
Keeping here incase someone needs it.

Answer 2

Replace in Dockerfile
COPY ${JAR_FILE} app.jar
with
COPY ${JAR_FILE} /app.jar

Answer 3

It might be late, however, for the people who encounter this problem and look for a solution in this post. This one might help.
If you are defining the ARG within the Dockerfile, for example: ARG JAR_FILE. When you build the image, don't forget to include the ARG with its value. For example:
docker build --build-arg JAR_FILE=target/*.jar -t [your_tag] .