production-ready dockerfile for python projects

Dockerfile

# syntax = docker/dockerfile:experimental

ARG PYTHON_VERSION=3.7.6
ARG APP_ENV=prod

# ---------------------------------------------------------------

FROM python:${PYTHON_VERSION}-stretch AS base-builder
ENV VIRTUAL_ENV=/opt/venv
RUN python -m venv ${VIRTUAL_ENV}

# ---------------------------------------------------------------

FROM base-builder AS prod-builder
COPY requirements.txt .
RUN --mount=type=cache,target=/root/.cache/pip \
    ${VIRTUAL_ENV}/bin/pip install -r requirements.txt

# ---------------------------------------------------------------

FROM prod-builder AS dev-builder
COPY requirements-dev.txt .
RUN --mount=type=cache,target=/root/.cache/pip \
    ${VIRTUAL_ENV}/bin/pip install -r requirements-dev.txt

# ---------------------------------------------------------------

FROM ${APP_ENV}-builder AS builder

# ---------------------------------------------------------------

FROM python:${PYTHON_VERSION}-slim-stretch AS base

ARG APP_USER=appuser
ARG APP_USER_UID=1000
ARG APP_ROOT=/app

ENV VIRTUAL_ENV=/opt/venv
ENV PATH="${VIRTUAL_ENV}/bin:${PATH}"

RUN useradd --create-home --uid=${APP_USER_UID} ${APP_USER} \
    && mkdir -p ${VIRTUAL_ENV} \
    && chown ${APP_USER}:${APP_USER} ${VIRTUAL_ENV}

WORKDIR ${APP_ROOT}

# ---------------------------------------------------------------

FROM base AS test
COPY --from=dev-builder --chown=${APP_USER}:${APP_USER} ${VIRTUAL_ENV} ${VIRTUAL_ENV}
COPY --chown=${APP_USER}:${APP_USER} . ${APP_ROOT}
CMD ["pytest"]

# ---------------------------------------------------------------

FROM base AS release
COPY --from=builder --chown=${APP_USER}:${APP_USER} ${VIRTUAL_ENV} ${VIRTUAL_ENV}
COPY --chown=${APP_USER}:${APP_USER} . ${APP_ROOT}
USER ${APP_USER}
EXPOSE 8000
RUN ["python"]