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

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

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@xxxxxxxxxx>
> > 
> > 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@xxxxxxxxxxxxxxxxxxxx"
> --------------------
> 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

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.


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=*".

Cheers,

-- 
Anthony PERARD