using the same Dockerfile to build images with different python version - makefile

Question

I have a python script that I'd want to run on 2 different containers running python 2.7 and python 3.6.
I want to use the same docker file to build 2 different images, with the difference being the python version(i.e one time it's FROM python:3.6 and the other is FROM python:2.7, and do it through a makefile.
Makefile
.PHONY = all clean build run
all: build run
# DOCKER TASKS
# Build the container
build: ## Build the container for tests
docker build -t myscript:python2.7 .
docker build -t myscript:python3.6 .
run: ## Run container
docker run myscript:python2.7
docker run myscript:python3.6
I have a Dockerfile for building the image:
Dockerfile
FROM python:3.6
WORKDIR /usr/local/bin
RUN pip install pytest
COPY myscript.py test_regex_script.py ./
CMD ["pytest", "test_regex_script.py"]
Since it's the same Docker file it's tricky, I was thinking to create two different Dockerfiles each with a different python version (and all the rest the same), but was wondering if there's more elegant way to do it.
thanks

Answer 1

You can use a build argument for it.
Your Dockerfile should look like this:
ARG VERSION=3.6
FROM python:3.6
WORKDIR /usr/local/bin
RUN pip install pytest
COPY myscript.py test_regex_script.py ./
CMD ["pytest", "test_regex_script.py"]
To build for 3.6:
docker build -t python-app:3.6 .
To build for 2.7:
docker build -t python-app:2.7 --build-arg VERSION=2.7 .
Note that 3.6 is the default version in case you don't specify one (ARG VERSION=3.6). You can also not assign a default value in which case you have to always pass a value in the build argument (--build-arg VERSION=...)

Answer 2

you can try updating the script mentioned above like
ARG PYTHON_VERSION=python:3.8-slim-buster
FROM python:${PYTHON_VERSION}
WORKDIR /usr/local/bin
RUN pip install pytest
COPY myscript.py test_regex_script.py ./
CMD ["pytest", "test_regex_script.py"]

Answer 3

Make sure ARG is at the very top of your Dockerfile.
ARG PY_VERSION=3.8
ARG NODE_VERSION=16
FROM node:$NODE_VERSION as frontend
FROM python:$PY_VERSION as backend
The FROM's can be lower in the file.
Default (python:3.8 and node:16):
docker build \
-t my-image \
-f Dockerfile \
.
Override Python (use 3.10 instead of 3.8):
docker build \
-t my-image \
-f Dockerfile \
--build-arg PY_VERSION=3.10 \
.
Override Node:
docker build \
-t my-image \
-f Dockerfile \
--build-arg NODE_VERSION=17 \
.
Override Both:
docker build \
-t my-image \
-f Dockerfile \
--build-arg PY_VERSION=3.10 \
--build-arg NODE_VERSION=17 \
.
You can also use buildx / docker buildx build:
docker buildx build \
-t my-image \
-f Dockerfile \
--build-arg PY_VERSION=3.10 \
--build-arg NODE_VERSION=17 \
.