apt-get not found in Docker - dockerfile

Question

I've got this Dockerfile:
FROM python:3.6-alpine
FROM ubuntu
FROM alpine
RUN apk update && \
apk add --virtual build-deps gcc python-dev musl-dev
RUN apt-get update && apt-get install -y python-pip
WORKDIR /app
ADD . /app
RUN pip install -r requirements.txt
EXPOSE 5000
CMD ["python", "main.py"]
and it's throwing error saying /bin/sh: apt-get: not found.
I thought apt-get package is part of Ubuntu image that I'm pulling on the
second line but yet it's giving me this error.
How can I fix this ?

Answer 1

as tkausl said: you can only use one base image (one FROM).
alpine's package manager is apk not apt-get. you have to use apk to install packages. however, pip is already available.
that Dockerfile should work:
FROM python:3.6-alpine
RUN apk update && \
apk add --virtual build-deps gcc python-dev musl-dev
WORKDIR /app
ADD . /app
RUN pip install -r requirements.txt
EXPOSE 5000
CMD ["python", "main.py"]

Answer 2

apt-get does not work because the active Linux distribution is alpine, and it does not have the apt-get command.
You can fix it using apk command.

Answer 3

most probbly the image you're using is Alpine,
so you can't use apt-get
you can use Ubuntu's package manager.
you can use
apk update and apk add

Answer 4

Multiple FROM lines can be used in a single Dockerfile.
See discussion and Multi stage tutorial
The use of Python Alpine, plus Ubuntu, plus Ubuntu is probably redundant. The Python Alpine one should be sufficient as it uses Alpine internally.
I had a similar issue not with apk but with apt-get.
FROM node:14
FROM jekyll/jekyll
RUN apt-get update
RUN apt-get install -y \
sqlite
Error:
/bin/sh: apt-get: not found
If I change the order, then it works.
FROM node:14
RUN apt-get update
RUN apt-get install -y \
sqlite
FROM jekyll/jekyll
Note, as in first link I added above, multiple FROMs might removed from Docker as a feature.