Dockerfile

FROM centos:7


RUN echo "tsflags=nodocs" >> /etc/yum.conf && \
    yum -y install epel-release && \
    curl -sL https://rpm.nodesource.com/setup_10.x | bash - && \
    yum -y install which crudini git git-annex obal tito mock scl-utils-build nodejs jq && \
    yum clean all

RUN git clone https://github.com/theforeman/foreman-packaging -b rpm/develop

RUN cd foreman-packaging ; git annex init ; ./setup_sources.sh

RUN npm install -g npm2rpm

to build:
put the Dockerfile and type

docker build -t build .

then execute docker run --interactive --rm -t build /bin/bash
inside you would find a /foreman_packaging folder