How does ENTRYPOINT Docker directive react when extending images

I want to know does react the ENTRYPOINT instruction from Dockerfiles when heritage happens :

Let’s say for example I have an image called : jenkins

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  • FROM java:8-jdk
    RUN ...
    ENTRYPOINT ["/bin/tini", "--", "/usr/local/bin/jenkins.sh"]
    

    By running this image, the ENTRYPOINT directive will start and install the application as expected

    Let’s say now that I want to extend this image with a new Dockerfile, I call it : jenkins-custom

    FROM jenkins
    
    # enable start tls
    RUN echo "JENKINS_JAVA_OPTIONS=\"-Dmail.smtp.starttls.enable=true\"" >> /etc/default/jenkins
    RUN chown jenkins:docker /etc/default/jenkins
    

    Should I consider that :

    1. the jenkins entrypoint is triggered after my new lines.
    2. entrypoint will be trigered before my new lines.
    3. entrypoint will not be triggered.

    In my example, I am trying to activate STARTTLS in default Jenkins docker image, should I just restart the process in the second image ?

    Thanks to all 😉

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  • One Solution collect form web for “How does ENTRYPOINT Docker directive react when extending images”

    The commands in ENTRYPOINT run when you execute docker run. However, commands in RUN are executed when you run docker build.

    In your case, what’s going to happen is that when you docker build the image, a new Jenkins configuration file is generated, and then when you docker run it, tini is launched, and in turns execute the jenkins-entrypoint.sh.


    If what you’re trying to do is change the Jenkins configuration and nothing else, what you have here is good.

    Docker will be the best open platform for developers and sysadmins to build, ship, and run distributed applications.