Spring system parameter is being ignored

Question

I created my Dockerfile where I want to create a simple Spring Boot Webapp listening on a port.

FROM java:8
VOLUME /tmp
ENV port=123
#WORKDIR /workdir
ADD /target/docker-test-0.1.jar dockertest.jar
EXPOSE $port
RUN bash -c 'touch /dockertest.jar'
#ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom -Dserver.port=$port","-jar","/dockertest.jar"]
ENTRYPOINT java -jar /dockertest.jar -Djava.security.egd=file:/dev/./urandom -Dserver.port=$port

My webapps application.properties defines the following:

server.port=666

Starting my docker container via IntelliJ Docker Plugin I give it the parameter:

port=555

Running docker inspect bootapp (bootapp is the containers name) gives me following information about the port environment variable and the entrypoint:

 "Entrypoint" : [ "/bin/sh", "-c", "java -jar /dockertest.jar -Djava.security.egd=file:/dev/./urandom -Dserver.port=$port" ],
    "Env" : [ "port=555", ...],

And Spring Boots log says this:

2017-08-30 20:10:07.709  INFO 5 --- [main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 666 (http)

So the port defined in application.properties was not overwritten by a runtime parameter.

This tells me that EXPOSE=$port actually was able to be resolved but the variable in ENTRYPOINT wasn't.

I already changed ENTRYPOINT to shell form but that did not helped as you can see through my Dockerfile

Answer 1

The system variable was at the wrong place in the java execution command. It has to be place before the -jar option.

Wrong

ENTRYPOINT java -jar /dockertest.jar -Djava.security.egd=file:/dev/./urandom -Dserver.port=$port

Right

ENTRYPOINT java -Dserver.port=$port -jar /dockertest.jar -Djava.security.egd=file:/dev/./urandom