Support automated ARM builds

[ahoarau]

Currently it is not possible to launch an automated arm build on the Hub because the hosts does not seem to have qemu-user-static.
Is there an alternate solution to this ?

[pchico83]

You could install the package is the post_checkout hook:
https://docs.docker.com/docker-cloud/builds/advanced/
It is also supported in Docker Hub.

[ahoarau]

Cool. So I shall create a docker-compose.test.yml file in my github repo, and docker hub will automatically read it ?

[pchico83]

Yes, that is possible. But you can also defined your own hooks.
For example, you could create a post_checkout file in a hooks folder at the level of your Dockerfile, and that script will be executed after checking out your github repo. You could use it to install apt-get packages (our build machines are Ubuntu Trusty).

[jcsrb]

@ahoarau did you create such a workflow, you link to it?

[ahoarau]

@jcsrb nope did not managed to make it work on the hub. Running locally instead.

[davidecavestro]

@pchico83 it works like a charm!
@ahoarau it turns out to be just a matter of registering qemu-arm-static before launching the build

See mariadb-docker-armhf (WIP):

.
├── Dockerfile
└── hooks
     ├── post_checkout
     └── pre_build

hooks/post_checkout

#!/bin/bash
# downloads a local copy of qemu on docker-hub build machines
curl -L https://github.com/balena-io/qemu/releases/download/v3.0.0%2Bresin/qemu-3.0.0+resin-arm.tar.gz | tar zxvf - -C . && mv qemu-3.0.0+resin-arm/qemu-arm-static .

hooks/pre_build

#!/bin/bash
# Register qemu-*-static for all supported processors except the 
# current one, but also remove all registered binfmt_misc before
docker run --rm --privileged multiarch/qemu-user-static:register --reset

Dockerfile

FROM arm32v7/debian:stretch-slim 
COPY qemu-arm-static /usr/bin
...

Probably it can be further reduced.
Now the job fails just for a matter of timeout (huge build) but the arm stuff simply works :-)

[ahoarau]

@davidecavestro excellent ! I guess the issue is closed now :)

[se1exin]

FYI this did not work for me - Docker Hub build cannot find the qemu-arm-static file:

...
Step 6/10 : COPY qemu-arm-static /usr/bin
COPY failed: stat /var/lib/docker/tmp/docker-builder403015795/qemu-arm-static: no such file or directory

I worked around it by removing the post_checkout file and using a builder/mutlistage Dockerfile to download the qemu-arm-static binary inside the container instead.

Example Dockerfile:

FROM golang:1.12.0 AS builder
# ... my go build steps (removed from this example)
WORKDIR /builder/working/directory
RUN curl -L https://github.com/balena-io/qemu/releases/download/v3.0.0%2Bresin/qemu-3.0.0+resin-arm.tar.gz | tar zxvf - -C . && mv qemu-3.0.0+resin-arm/qemu-arm-static .

FROM arm32v7/alpine:latest
# Copy across the qemu binary that was downloaded in the previous build step
COPY --from=builder /builder/working/directory/qemu-arm-static /usr/bin
# Now you can tun ARM docker steps.. yay!

Note I'm using golang as my builder image, but I'm sure any amd64 image with curl and tar would work fine. My full Dockerfile is here if it might help anyone: https://github.com/se1exin/Hue-Im-Home/blob/a39ab7c78db2564f767527519d18d8c1faf964cd/docker/Dockerfile.arm32v7