Dockerfile quicky - templating with M4

Creating abstracted Dockerfile is something I really wish existed. Every time, I write a Dockerfile for a specific base image I must specify the correct package manager command. I must call apt-get or apk or yum or any other call for the package manager. This is unfortunately, not very reusable.

I am comparing this to many years of experience with salt-stack which includes a great wrapper around many common Linux package managers. This spares the details of distinguishing between apt, apk or yum and dnf, you just write pkg.install and you get your packages installed.

Here is a simple M4 schema how to achieve this abstraction. A better solution will probably involve Jinja2 templates ... This can spare you the need to remember which package manager you need to use in which Docker image. Here is a very quick intro, how to this.

First create an m4 template:

$ cat Dockerfile.in 
FROM ifdef(`ALPINE', alpine, ubuntu)
MAINTAINER Oz N Tiram <oz.tiram@gmail.com>

RUN ifdef(`ALPINE', apk add --update --no-cache, 
          apt-get update && apt-get install -y) curl tar xz bash

Now, create a simple Makefile:

$ cat Makefile 
ALPINE ?=

ifdef ALPINE
    USE_ALPINE := -DALPINE
endif

dockerfile:
    @m4 $(USE_ALPINE) Dockerfile.in

Now you can create Dockerfile for your image from Ubuntu with:

$  make > Dockerfile

Or you can create a Dockerfile based on Alpine Linux:

$ make ALPINE=1 > Dockerfile