Nix with Flakes support on top of ubuntu:20.04 docker

Dockerfile

FROM ubuntu:20.04

ENV DEBIAN_FRONTEND noninteractive

RUN apt-get update \
    && apt-get --yes install curl xz-utils sudo \
    && apt-get clean && rm -rf /var/lib/apt/lists/ \
    && useradd -m -G sudo --password "!" --shell /bin/bash my-user \
    && (echo 'my-user ALL=(ALL) NOPASSWD: ALL' >> /etc/sudoers)

USER my-user
ENV USER=my-user
WORKDIR /home/my-user
ENTRYPOINT /bin/bash

RUN (curl -L "https://github.com/numtide/nix-flakes-installer/releases/download/nix-2.4pre20210429_d15a196/install" | \
     sh -s -- --no-daemon) \
    && sudo apt-get --yes purge curl xz-utils \
    && sudo mkdir /etc/nix \
    && echo 'experimental-features = nix-command flakes ca-derivations ca-references' | sudo tee -a /etc/nix/nix.conf \
    && echo 'PATH=$HOME/.nix-profile/bin:$PATH' | sudo tee -a /etc/bash.bashrc \
    && echo 'source $HOME/.nix-profile/etc/profile.d/nix.sh' | sudo tee -a /etc/bash.bashrc \
    && export "PATH=$HOME/.nix-profile/bin:$PATH" \
    && nix store optimise