[CentOS-devel] [altarch] multiarch docker images

[Manfred Touron]

Hi everyone,

I'm working at Scaleway on the multiarch images system,
I'm @moul on IRC and talked with @Arrfab and @Evolution (thanks a lot, guys).

---

Context: Today, we are using Docker as a build-step to generate
our baremetal servers rootfs, what we call, the "Scaleway images".

Here is an example of "1 click app" image:

- Public Hub: https://hub.scaleway.com/wordpress.html
- DevHub (aggregate APIs): http://devhub.scaleway.com/#/images/wordpress:latest
- Source (GitHub): https://github.com/scaleway-community/scaleway-wordpress/
- Docker Hub: https://hub.docker.com/r/scaleway/wordpress/
- Build logs: https://travis-ci.org/scaleway/qa/builds/98515979

We are quite happy today with this method and are succesfully running
plenty Linux distributions (Ubuntu, openSUSE, Gentoo, Fedora, Debian,
Arch Linux and Alpine Linux).

Actually we also have a proof-of-concept of CentOS image, but based
on an old development CubieTruck snapshot with no public mirrors.

Here is how I built this POC image (I wasn't aware of virt-tar-out):
https://github.com/armbuild/centos-img/blob/master/buildcontainers.sh

---

We will soon release new server models with new architectures, our next
priorities are: `arm64` and `x86_64`, but we plan to support more architectures
if we feel enough people will need it so the development worth it.

I started to work on "multiarch" images (one image per architecture).
Here are some images:

- https://github.com/multiarch/alpine
    -> built with `apk-static` in a chroot
- https://github.com/multiarch/busybox
    -> static binaries extracted from latest busybox-static.deb
- https://github.com/multiarch/ubuntu-debootstrap
    -> qemu-debootstrap
- https://github.com/multiarch/debian-debootstrap
    -> same as above
- https://github.com/multiarch/ubuntu-core
    -> based on released rootfs tarballs at
       https://partner-images.canonical.com/core/wily/current/

All those images also contains an `x86_64` `qemu-${ARCH}-static` so
you can run them on an `x86_64` host with `binfmt-support` available.
Look at the README.md files for usage and examples.

I began to work on the Centos image https://github.com/multiarch/centos,

I successfully built the `armhf` and `arm64` images by `virt-tar-out`ing
the CubieTruck released image, i.e.:
http://mirror.centos.org/altarch/7.2.1511/isos/armhfp/

I also successfully built the `x86_64` and `i386` images using kickstart:

    livemedia-creator --arch=i386 --make-disk         \
                      --iso=/tmp/boot7-i386.iso       \
                      --ks=$(pwd)/centos-7.ks         \
                      --image-name=centos-7-base-i386

based on https://github.com/CentOS/sig-cloud-instance-build/tree/livemedia_builds/docker

For now I failed to build the `ppc64` nor `ppc64le` images, but that's not a
priority.

I have now an issue, my `armhf` and `x86_64` images are not the same,
the ones based on real boards .img.xz embed about 300M of kernel images,
dtb, kernel modules, firmware (I don't want them) + a lot more apps that we
can find by default in the <200Mb `x86_64` Docker image.

I would like to find a solution to build "same" images for all the targets
and avoid as much as possible the need of diffing the outputs of
`yum list installed`.

My favorite solution would be to use kickstart files, which are very cool
to put on GitHub. But the non `x86_64` architectures lack of a `boot.iso`
file packing `isolinux`.

Is it possible to add those `boot.iso` files on the mirror or tell
me how to build them ?
Do you see alternative ways to build identical images ?

--
Manfred Touron - @moul
CTO @ scaleway.com
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