Dockerfile from ubuntu:22.04 with asdf + python 3.6.9 thanks to PYTHON_CFLAGS='-O2'

Dockerfile

# inspired by:
# https://gist.github.com/BrutalSimplicity/882af1d343b7530fc7e005284523d38d
# and minimized thanks to:
# https://stackoverflow.com/questions/72102435/how-to-install-python3-6-on-ubuntu-22-04
FROM ubuntu:22.04

# ensure we use bash for all RUN commands
# use -l to use interactive login shell
# and ensure modifications to bashrc are properly sourced
SHELL ["/bin/bash", "-lc"]

# Install basic dev packages
RUN apt-get clean && apt-get update && DEBIAN_FRONTEND=noninteractive apt-get -y install --no-install-recommends \
    make build-essential libssl-dev zlib1g-dev \
    libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm libncurses5-dev \
    libncursesw5-dev xz-utils tk-dev libffi-dev liblzma-dev \
    libgdbm-dev libnss3-dev libedit-dev libc6-dev \
    git \
    && rm -rf /var/lib/apt/lists/*

RUN apt-get clean && apt-get update && DEBIAN_FRONTEND=noninteractive apt-get -y install --no-install-recommends \
    ca-certificates \
    && rm -rf /var/lib/apt/lists/*

# installing openssl because saw this in /tmp/python-build*.log:
# warning: openssl 0x00000000 is too old for _hashlib
RUN apt-get clean && apt-get update && DEBIAN_FRONTEND=noninteractive apt-get -y install --no-install-recommends \
    openssl \
    && rm -rf /var/lib/apt/lists/*

RUN git config --global advice.detachedHead false
RUN git clone https://github.com/asdf-vm/asdf.git ~/.asdf --branch v0.11.3
# prepending asdf because bash knows we are not interactive and returns early from .bashrc
RUN sed -i '1s;^;source $HOME/.asdf/asdf.sh\nsource $HOME/.asdf/completions/asdf.bash\n;' ~/.bashrc

RUN asdf plugin add python
# prefixing "asdf install" due to https://stackoverflow.com/questions/70064631/python3-5-m-ensurepip-segmentation-fault
# CC=clang would be the other solution, but "apt install clang" says "557 MB of additional disk space will be used"
RUN PYTHON_CFLAGS='-O2' asdf install python 3.6.9
RUN echo XXXXX
RUN cat /tmp/python-build*.log
RUN echo YYYYY
RUN asdf global python 3.6.9

RUN pip install --upgrade pip
# RUN pip install pipenv

RUN python3 --version
RUN pip3 --version

RUN \
  pip3 install --no-cache-dir -i https://artifactory.funkwerk-itk.com/api/pypi/pypi-virtual/simple --upgrade \
    setuptools==59.6.0 gcovr pep8==1.7.1 pylint==2.10.2 autopep8==1.3.5 pydocstyle==2.1.1 pycodestyle==2.3.1 \
    flake8==3.5.0 flake8-blind-except==0.1.1 flake8-docstrings==1.3.0 autoflake==1.1 \
    flake8_quotes==0.13.0 flake8-isort==3.0.1 mccabe==0.6.1 pyflakes==1.6.0 \
    autobahn selenium==3.13.0 behave==1.2.6 aiohttp==3.6.2 pymongo polib==1.1.0 \
    psycopg2-binary \
    docker==3.2.1 dockerpty==0.4.1 ipywidgets pyaml

# make pylint and whatnot available by reshimming
RUN asdf update && asdf reshim python 3.6.9

# Set the working directory
WORKDIR /app

# Copy your application files to the container (if needed)
COPY . /app

# Specify the default command to run when the container starts
CMD ["python", "your_script.py"]

# set all the things to be sure bash is always used as the default shell
RUN cd /bin && ln -sf bash sh && chsh -s /bin/bash
ENV SHELL=bash
ENV PATH=$PATH:/root/.bin
ENTRYPOINT [ "/bin/bash", "-lc" ]

got as far as being able to run our 3.6.9 based python code successfully under ubuntu 22.04 where normal python is 3.10.

however, only as root: we have an elaborate dev container spawner script that calls "useradd" and mimicks the host $USER inside the fresh container, and I haven't been able to make it transparently "source" the asdf initialization scripts or do the re-shimming, even after installing asdf under /opt instead of /root and following asdf-vm/asdf#577

so for now I'm giving up on 3.6.9 under ubuntu 22.04 and will try to instead upgrade our python code.