Re: [PATCH] automation: set architecture in docker files

["Roger Pau Monné" <roger.pau@citrix.com>]

On Tue, Nov 14, 2023 at 03:00:17PM +0000, Anthony PERARD wrote:
> On Tue, Nov 14, 2023 at 10:01:06AM +0100, Roger Pau Monné wrote:
> > On Mon, Nov 13, 2023 at 04:10:24PM -0800, Stefano Stabellini wrote:
> > > On Mon, 13 Nov 2023, Roger Pau Monne wrote:
> > > > Pass the desired architecture of the image in the FROM instruction if the
> > > > image is possibly multi-platform.
> > > > 
> > > > This allows using the x86 Dockerfiles on OS X on arm64 hardware.
> > > > 
> > > > No functional change intended.
> > > > 
> > > > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> > > 
> > > Although I am not opposed to this change, so far we have been using:
> > > arm64v8/alpine:3.18
> > > 
> > > for x86 it is not specified but it would be:
> > > amd64/alpine:3.18
> > > 
> > > Two options:
> > > 1) we add amd64/ everywhere and leave the arm containers alone
> > > 2) we change all containers, including the arm containers, to use the
> > > --platform option
> > > 
> > > I don't think is a good idea to have 2 different ways to specify the
> > > architecture for x86 and arm containers
> > 
> > I'm not an expert on this, but attempting to use (2):
> > 
> > -FROM arm64v8/alpine:3.18
> > +FROM --platform=linux/arm64v8 alpine:3.18
> > 
> > Does not work for me:
> > 
> > % make -C automation/build alpine/3.18-arm64v8
> > docker build --pull -t registry.gitlab.com/xen-project/xen/alpine:3.18-arm64v8 -f alpine/3.18-arm64v8.dockerfile alpine
> > [+] Building 1.4s (3/3) FINISHED                                                  docker:desktop-linux
> >  => [internal] load .dockerignore                                                                 0.0s
> >  => => transferring context: 2B                                                                   0.0s
> >  => [internal] load build definition from 3.18-arm64v8.dockerfile                                 0.0s
> >  => => transferring dockerfile: 818B                                                              0.0s
> >  => ERROR [internal] load metadata for docker.io/library/alpine:3.18                              1.4s
> > ------
> >  > [internal] load metadata for docker.io/library/alpine:3.18:
> > ------
> > 3.18-arm64v8.dockerfile:1
> > --------------------
> >    1 | >>> FROM --platform=linux/arm64v8 alpine:3.18
> >    2 |     LABEL maintainer.name="The Xen Project" \
> >    3 |           maintainer.email="xen-devel@lists.xenproject.org"
> > --------------------
> > ERROR: failed to solve: alpine:3.18: no match for platform in manifest sha256:eece025e432126ce23f223450a0326fbebde39cdf496a85d8c016293fc851978: not found
> > make: *** [alpine/3.18-arm64v8] Error 1
> > 
> > That's why I've left the prefixed images alone.
> > 
> > I could prefix the x86 images with amd64/ if that's preferred, I
> > didn't try that option, as the Docker manual suggested using
> > --platform.
> 
> So a few things to know, "--platform=linux/amd64" just select a
> different build of one container. For example, for the "alpine"
> containers, you can see all the different builds available on the docker
> hub, here a few links:
> - Official Docker, Alpine images, home:
>   https://hub.docker.com/_/alpine
> - The different builds: 
>   https://hub.docker.com/_/alpine/tags
> 
> So, for amd64v8, you probably want --platform=linux/arm64/v8

Interesting, I guess I was looking at an outdated documentation that
stated the tag as arm64v8 instead of arm64/v8.

> 
> Then, they are per-architecture repository that make it easier to deal
> with foreign architecture, and probably maintained by a different
> community. e.g. for alpine arm64v8:
>     https://hub.docker.com/r/arm64v8/alpine/
> 
> Those provide a build for a single architecture.

Right, so those two are not actually the same image.  I wonder whether
we would want to uniformly switch to using --platform when possible,
in order to make sure we are using the same (multi arch) image to
avoid surprises.

> 
> 
> Sometime, you actually need to "--platform=*" to select a particular
> architecture, like I did for "jessie-i386.dockerfile".
> 
> 
> One thing I've notice when using --platform is that, if for example I
> use the container "--platform=linux/amd64 alpine:3" then
> "--platform=linux/arm/v6 alpine:3"; later when I only specify
> "alpine:3", it's going to be the armv6, and I think docker is going to
> complain if I try tu use "--platform=linux/amd64 alpine:3" without
> "docker pull" first (or I guess docker build --pull).
> 
> Hope that help.
> 
> So I guess using containers "amd64/*" or "arm64v8/*" is fine, but
> sometime will need to use "--platform=*".

My take is that it's better to use --platform when possible, as then
all platforms share the same image, and the contents of the image
should be more consistent.

I guess we could see about switching some of the image that currently
use a prefix (like the Alpine one) in order to instead use --platform
and share the same image.  I wouldn't want to do it in this patch
however, as the change presented here should be non-functional, while
switching to the multi arch image might introduce changes.

Thanks, Roger.