Docker arg not being read correctly from command line - docker

Question

Using this command to start and run my docker container passing in argument ./target/myapp-SNAPSHOT.jar where ./target/myapp-SNAPSHOT.jar is the Spring boot app I wish to run :
docker build -t foo . && docker run -it foo -e J_FILE=./target/myapp-SNAPSHOT.jar
I receive error :
standard_init_linux.go:211: exec user process caused "exec format error"
Dockerfile:
FROM adoptopenjdk/openjdk8:alpine-jre
LABEL app.name="test"
LABEL app.type="test"
ARG J_FILE
ADD ${J_FILE} /myapp.jar
COPY J_FILE /myapp.jar
COPY startup.sh /
RUN chmod +x startup.sh;
ENTRYPOINT ["/startup.sh"]
EXPOSE 8080
startup.sh :
#!/bin/sh
JAVA_HEAP_INITIAL=384m
JAVA_HEAP_MAX=768m
JAVA_METASPACE_MAX=128m
java -jar /app.jar
If I change Dockerfile to explicitly copy the jar file :
FROM adoptopenjdk/openjdk8:alpine-jre
LABEL app.name="test"
LABEL app.type="test"
COPY ./target/myapp-SNAPSHOT.jar /myapp.jar
COPY startup.sh /
RUN chmod +x startup.sh;
ENTRYPOINT ["/startup.sh"]
EXPOSE 8080
The app starts as expected.

Answer 1

The ARG flag in Dockerfile is meant for configuration when building a docker image. It will not have any effect when you run the container.
Therefore, you should update your command to be like this:
docker build --build-arg J_FILE=./target/myapp-SNAPSHOT.jar -t foo . && docker run -it foo
You can also update your Dockerfile to be like this:
FROM adoptopenjdk/openjdk8:alpine-jre
LABEL app.name="test"
LABEL app.type="test"
ARG J_FILE=./target/myapp-SNAPSHOT.jar
COPY ${J_FILE} /myapp.jar
COPY startup.sh /
RUN chmod +x startup.sh;
ENTRYPOINT ["/startup.sh"]
EXPOSE 8080
Note 2 changes in the file above:
Use COPY instead of ADD
Set the default value for J_FILE as ./target/myapp-SNAPSHOT.jar in case the --build-arg is not passed with the docker build command.