Dockerfile contd

• RUN: This instruction RUNs a command during image building
• WORKDIR
• ARG: This is build argument which can be passed during image build
• ENTRYPOINT:
  • if entrypoint exists in Docker file that will be default executable. whatever we write in CMD will become arguments to entrypoint
  • if entrypoint is not found then CMD will be executable
  • CMD can be overriden easily by passing additional commands post image name in docker run
  • Note: watch classroom video
• docker run command by default runs in attached mode where as -d will run in detached mode i.e in background
• We can also run a contaier in an interactive mode

docker run -it alpine /bin/sh

Sample Application – Java

• Running the application as a non root user
• Lets create a user called as spc, and copy the jar file into user’s home directory
• Refer Here for the changes
  
• Refer Here for changes to include workdir as /apps
• Lets parametrize the username and source for downloading petclinic
  

Shell form and Exec Form

• Shell form is where you can write the commands directly apt update
• Exec form is where you follow json array syntax ["apt", "update"]
• Shell form:
  • in a windows container this runs with CMD
  • in a linux contianer this runs with /bin/sh
  • This can expand variables ${USERNAME}
  • This does not handle SIGTERM i.e. it cannot handle docker stop correctly
  • where to use:
    • RUN
• Exec form:
  • Runs the command directly
  • No variable expansions
  • This works well with SIGTERM
  • Where to use
    • ENTRYPOINT
    • CMD