How do I know that Alpine is the base image for my container?

General Discussions
1

Hello,

I am new to this Docker technology/platform.
I have created 2 examples and for the first one Dockerfile looks something like this

FROM python:3.6

RUN mkdir src
ADD testclient.py /src/
RUN pip install pyzmq

…

And for the second one Dockerfile looks something like this

FROM alpine:3.7
RUN apk update

FROM python:3.6
RUN pip install pyzmq

RUN mkdir src
ADD testclient.py /src/

…

How will I validate that Alpine is the base image for container that is created out of the second example?

Many thanks in advance.

Regards,
Sakar

2

It will not be because python:3.6 is built on Debian Stretch. If you want it to be based on Alpine, why don’t you use python:3.6-alpine directly?

3

Thanks for the suggestion. I used the same in my next trial.
I have another issue to address now

FROM python:3.6-alpine

RUN apk --no-cache update
RUN apk --no-cache add build-base
RUN apk --no-cache add libzmq
RUN apk --no-cache add zeromq-dev

RUN pip3 install pyzmq

reduce image size by cleaning up the build packages

RUN apk del build-base zeromq-dev

RUN mkdir src
ADD test.py /src/

WORKDIR /src/
…

How do I reduce the image size to whatever least possible with above Dockerfile specifications?
Currently it is reporting about 196 MB…

Any suggestions?

Regards,
Sakar Kalkotwar

4

First you could combine the different RUN commands into one. Then you could combine the build dependencies into a virtual package

RUN apk --update add --virtual ...

and remove this after pip3 install, as described here.
But in general I wouldn’t worry too much about the size of a single image and instead to try to limit the overall size of the system. Images consist of several layers (from the docs: “Each instruction in a Dockerfile creates a layer in the image.”). If you build all the images in the same way many of these layers will be shared between them and don’t require additional space.