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" ]

focusing on python; if we install aptitude we see that python3.10 is brought by lsb-release: aptitude why python3.10

dive shows the largest layer is 797MB, of which:
102MB occupied by /usr/lib/gcc,
101MB by /usr/bin
390MB by /usr/lib/x86_64-linux-gnu
114MB by /usr/share

should look into https://www.augmentedmind.de/2022/02/06/optimize-docker-image-size/

unfortunately I do need python 3.6.9 and trying to install it I get a segmentation fault, similar to
https://stackoverflow.com/questions/72102435/how-to-install-python3-6-on-ubuntu-22-04

even after adding all packages mentioned in the SO answer:

    libncurses5-dev \
    libgdbm-dev \
    libnss3-dev \
    libedit-dev \
    libc6-dev \

I get

Downloading python-build...
Cloning into '/root/.asdf/plugins/python/pyenv'...
python-build 3.6.9 /root/.asdf/installs/python/3.6.9
Downloading Python-3.6.9.tar.xz...
-> https://www.python.org/ftp/python/3.6.9/Python-3.6.9.tar.xz
Installing Python-3.6.9...

BUILD FAILED (Ubuntu 22.04 using python-build 2.3.20-3-g38ac7472)

Inspect or clean up the working tree at /tmp/python-build.20230615163935.85
Results logged to /tmp/python-build.20230615163935.85.log

Last 10 log lines:
if test "xupgrade" != "xno"  ; then \
        case upgrade in \
                upgrade) ensurepip="--upgrade" ;; \
                install|*) ensurepip="" ;; \
        esac; \
        LD_LIBRARY_PATH=/tmp/python-build.20230615163935.85/Python-3.6.9 ./python -E -m ensurepip \
                $ensurepip --root=/ ; \
fi
Segmentation fault (core dumped)
make: *** [Makefile:1102: install] Error 139
The command '/bin/bash -lc asdf install python 3.6.9' returned a non-zero code: 1

I'm not the only one experiencing similar issue with asdf in ubuntu 22.04: even with newer python 3.7.3
asdf-community/asdf-python#151

https://stackoverflow.com/questions/70064631/python3-5-m-ensurepip-segmentation-fault

... fix installation via pyenv, asdf and probably others:
export PYTHON_CFLAGS='-O2'

others got around it (?) by CC=clang or building python 3.7.12

pyenv/pyenv#2141

could not pin pylint==2.10.2 (installs fine but then bash: pylint: command not found), without pinning getting 2.13.9 just fine

nah, same, until I do RUN asdf update && asdf reshim python 3.6.9

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.