docker-alpine-templates
This is my collection of useful snippets, best practices and how-tos for docker images built with alpine linux as their base (and some directions if you are coming from a debian based docker image base).
A part of this repo is used for automated builds on dockerhub: https://hub.docker.com/u/josefcs/
Also, ready to clone as a starting base for your own projects :-)
Motivation
Moving from debian (and ubuntu linux) to alpine linux as docker base does indeed save a lot of time and space for the images their builds. But on the other hand, if you are not yet familiar with alpine (like I am), you need to learn a few new things - and possibly invest the saved time into alpine.
From debian to alpine linux
The first thing I noticed was: alpine seems to keep more to the standards the
package was delivered with. E.g. the package apache2: Originally,
the executable is called httpd (apache2 in debian), the config resides in
/etc/httpd and has no subdirectories like /etc/apache2/sites-available in
debian.
So, you need to check at first, what the difference from the to-be installed
package to the debian package is. Migration is not always fast and easy, but
in most cases straightforward.
In some cases, the Dockerfile is smaller and lighter than before. Look at
alpine-cron and how simple it is. The original debian setup was a little bit
more complicated ;-)
In other cases, the Dockerfile can become more complicated (at least for me).
e.g. mysql-server or apache2-setup.
Description of images
My intention is to use as much provided content as possible. i.e. use the packages provided by alpine and not check them out and build them from source. Also I try to keep it as simple as possible, i.e. no complicated setup or init scripts. Configuration should be as straight forward as possible.
cron
Only used as a template, to copy the ENTRYPOINT line to your project. No automated builds because there is no need to install cron, as it is included automatically in alpine due to busybox.
nginx
Basic nginx from the package provided by alpine. This is a work in progress and config files have yet to be set up. Once it is fully working, it will move into its own repo.
nginx-php
See "nginx", but also php support. This should one day be able to run PHP/Zend programs.
Best practices
busybox
alpine uses busybox for its basic shell commands, which need different
parameter names than the 'normal' linux distro tools. That means you should
look up the commands at https://busybox.net/downloads/BusyBox.html and cannot
use the man pages from the net (or your host distro). This also implies that if
you already had setup scripts with adduser (or useradd), you have to migrate
them.
bash
bash is not installed by default in alpine, but you can install it with
apk-install bash. However, I would suggest that you move your shell scripts to
sh if possible. This means, if you want to shell into a container, you have to
run
docker exec -it my_instance sh
instead of
docker exec -it my_instance bash
Searching for packages
You can find the packages at https://pkgs.alpinelinux.org/packages. From my
experience, the packages are very well maintained and all "big" packages are
there.
To find a package, enter the name you know from your distro and add a % at the
end. In some cases when there is no installation candidate (like cron/crond),
it is built in due to busybox.
I don't know yet, what to do if the desired package does not exist in alpine (except from writing a build script within the Dockerfile).
Creating the Dockerfile
TODO:
- Find out what package to install (pkgs online)
- Test the installation (run cmd)