Docker image/container - use aptitude

In your docker build try this sequence:

USER root
RUN apt-get clean -yq && apt-get update -yq && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends openjdk-11-jdk
USER ${ISC_PACKAGE_MGRUSER}

Or install sudo (very bad practice in containers):

USER root
RUN apt-get clean -yq && apt-get update -yq && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends tzdata curl gnupg ca-certificates sudo
RUN /bin/echo -e ${ISC_PACKAGE_MGRUSER}\\tALL=\(ALL\)\\tNOPASSWD: ALL >> /etc/sudoers
RUN sudo -u ${ISC_PACKAGE_MGRUSER} sudo echo enabled passwordless sudo-ing for ${ISC_PACKAGE_MGRUSER}
USER ${ISC_PACKAGE_MGRUSER}

Hi @Dmitrii Baranov!

Check this basic iris-dev template on the Open Exchange. As you can see it installs git in Dockerfile changing user to root and back to iris-owner:

## install git
## USER root   
##RUN apt update && apt-get -y install git
##USER ${ISC_PACKAGE_MGRUSER}

if uncommented it installs git via user root. I hope this is what you wanted.