Run java program and shell script on entrypoint in Dockerfile

Question

I have base docker image where I have a Dockerfile which has an entry like follows

CMD ["/bootstrap.sh"]

In my child docker image where I am referencing this parent docker image, I have a separate entrypoint which starts my container as java program like below

ENTRYPOINT exec java -Duser.timezone=GMT -Djava.security.egd=file:/dev/./urandom $JAVA_OPTS -jar /app.jar

When I build this child docker image and try to run it, only the java program is coming up. bootstrap,sh is not building up.

After going through some blogs and stackoverflow posts, I cam to know in the child image, CMD context from parent image is lost and overwritten by child image entrypoint. However, I would like to run both shell script as well as java program on entrypoint. In my shell script, I jhave few executables reference which I require it to run and they will keep running the shell programs in background which my Java code will call to and do the processing based on these shell programs.

I also did try to combine both of these steps into one entrypoint like below but then this is only starting up one process - either shell script or Java program depending on which is specified first in dockerfile

ENTRYPOINT /bootstrap.sh && exec java -Duser.timezone=GMT -Djava.security.egd=file:/dev/./urandom $JAVA_OPTS -jar /app.jar

How can I specify in Dockerfile so that it can execute both the processes on startup of the container. bootstrap.sh can be run in background also.

Please help me on this one.

Usually if you need two processes, it's best to start them as two separate containers. I'd recommend changing the JVM invocation to CMD java ..., which will make it easy to run a second container with an alternate command docker run ... the-image /bootstrap.sh. — David Maze
This docker finally be run in both docker-compose as well and in kubernetes. docker run will be to start the container manually. What will be the equivalent in docker-compose and Kubernetes then where I can provide /bootstrap.sh to kick in? — ashishb
Fully agree with @DavidMaze: your java program on the one hand, and your services launched by bootstrap.sh should be in two different containers. BTW, note that an ENTRYPOINT command should always be in exec form (i.e., with ["…", "…"]), otherwise the CMD spec is ignored (even if you specify CMD after ENTRYPOINT). For details, see that other SO thread CMD doesn't run after ENTRYPOINT in Dockerfile. — ErikMD
did you find a way to run both java and shell script together in one command — subhajit biswas

ashishb ashishb · Accepted Answer · 2021-03-30T18:25:18

For those who are struggling, I was somehow able to resolve this issue. I don't know if this is the perfect solution but it worked for me.

What I did was I created another shell script file and I called bootstrap.sh from here followed by Java program.

Script file was something like this:

#!/bin/bash

echo "[server-startup] Executing bootstrap script"
/bootstrap.sh &

echo "[server-startup] Starting java application"
exec java -Duser.timezone=GMT -Djava.security.egd=file:/dev/./urandom $JAVA_OPTS -jar /app.jar

And my Dockerfile entry was modified like below where it called this new shell script file created above.

ENTRYPOINT ["/server-start.sh"]

Hope this helps who's looking for the answer.

Run java program and shell script on entrypoint in Dockerfile

1 Answers