#206 for ARM with Docker
Building 32-bit ARM v7 images with docker, tested on MacOS and AWS.
Notes
I’m running on MacOS and have access to Linux/AMD64 machines, but want to build a Docker image for 32-bit ARM v7 that I could then use with older Raspberry Pi or Odriod devices.
Here’s a demonstration of one way to do it, using Docker Buildx.
Docker Buildx
Docker Buildx is a CLI plugin that includes cross-platform build capability.
With Docker Desktop for Mac, buildx is available after enabling experimental features
Buildx availability can be confirmed by listing builders:
$ docker buildx ls
NAME/NODE DRIVER/ENDPOINT STATUS PLATFORMS
default * docker
default default running linux/amd64, linux/arm64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/arm/v7, linux/arm/v6
NB: if BUILDX_NO_DEFAULT_LOAD environment variable is not set, build commands will throw a warning.
Interestingly, there are many references to be found about the warning message, but little if any detail
on what BUILDX_NO_DEFAULT_LOAD is for in the first place. As far as I can figure:
- setting
truewill mean that build result will only remain in the build cache if no moby driver is available - probably want it to be false (the default)
- see sources in build.go
Testing a basic linux/amd64 image
The armi project includes a simple diagnostic program in c - based on the example from Getting started with Docker for Arm on Linux
The default builder can only build for a simple platform at a time. First I’ll build for linux/amd64 and test it running on MacOS.
cd armi
$ docker buildx build --platform linux/amd64 -t tardate/armi:amd64 .
...
=> exporting to image
=> => exporting layers
=> => writing image sha256:e62a7447cd15f6e9dfcc13eaa7dcbe49e3c892d546d200005aa8538403a1289c
=> => naming to docker.io/tardate/armi:amd64
$ docker run --rm tardate/armi:amd64
Hello, my architecture is Linux buildkitsandbox 4.19.76-linuxkit #1 SMP Tue May 26 11:42:35 UTC 2020 x86_64 Linux
$ docker run --rm -it --entrypoint sh tardate/armi:amd64
/home # ls
build.log hello hello.c
/home # cat build.log
I am running on linux/amd64, building for linux/amd64
Note:
- I’m not pushing an image to a remote repository at this stage (no
--pushparameter) - the default build knows how to load the image for docker use - hence
exporting to image...step - with non-default builders, I had to add the
--loadparameter to tell them to export the image for local docker use
Building for ARM
$ docker buildx build --platform linux/arm/v7 -t tardate/armi:arm .
$ docker run --rm tardate/armi:arm
Hello, my architecture is Linux buildkitsandbox 4.19.76-linuxkit #1 SMP Tue May 26 11:42:35 UTC 2020 armv7l Linux
$ docker run --rm -it --entrypoint sh tardate/armi:arm
/home # ls
build.log hello hello.c
/home # cat build.log
I am running on linux/amd64, building for linux/arm/v7
/home #
Building multi-platform images
I need to create a builder that will support multi-platform builds. I gave ti the random name myxbuilder:
$ docker buildx create --name myxbuilder
$ docker buildx inspect myxbuilder --bootstrap
Name: myxbuilder
Driver: docker-container
Nodes:
Name: myxbuilder0
Endpoint: unix:///var/run/docker.sock
Status: running
Platforms: linux/amd64, linux/arm64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/arm/v7, linux/arm/v6
Switching to use myxbuilder, I can build and push images to docker hub:
docker buildx use myxbuilder
docker buildx build --platform linux/arm/v7,linux/amd64 -t tardate/armi . --push
Inspecting the image manifest from docker hub, I see the two platform versions available under the same tag:
$ docker buildx imagetools inspect tardate/armi:latest
Name: docker.io/tardate/armi:latest
MediaType: application/vnd.docker.distribution.manifest.list.v2+json
Digest: sha256:fd9a3e0a54242ab3fd9c102ae617b2974aaee97c396d1bb66225a4e78844d409
Manifests:
Name: docker.io/tardate/armi:latest@sha256:e10bbaedfbbe5053cdcbc406ff87cff3da28c866fa3901a67b67f261d05baede
MediaType: application/vnd.docker.distribution.manifest.v2+json
Platform: linux/arm/v7
Name: docker.io/tardate/armi:latest@sha256:b9aa5b0c52abe4f00ae27499088ce751380c60b662a3a25fdc8e6e6757d1ff0e
MediaType: application/vnd.docker.distribution.manifest.v2+json
Platform: linux/amd64
Here’s how it appears at https://hub.docker.com/r/tardate/armi/tags:
Running these images by specific tag:
$ docker run --rm tardate/armi:latest@sha256:e10bbaedfbbe5053cdcbc406ff87cff3da28c866fa3901a67b67f261d05baede
Hello, my architecture is Linux buildkitsandbox 4.19.76-linuxkit #1 SMP Tue May 26 11:42:35 UTC 2020 armv7l Linux
$ docker run --rm tardate/armi:latest@sha256:b9aa5b0c52abe4f00ae27499088ce751380c60b662a3a25fdc8e6e6757d1ff0e
Hello, my architecture is Linux buildkitsandbox 4.19.76-linuxkit #1 SMP Tue May 26 11:42:35 UTC 2020 x86_64 Linux
Running the ARM Image on AWS
Roughly following the guide from Setting up an Arm server..
It seems that no cloud providers offer 32 bit instances any longer - Scaleway used for have 32 bit AMD “C1” machines but they have long since been retired.
AWS does offer 64 bit AMD instances, so I will test the docker image there (should not have any issue with 32 bit image).
Here’s the basic cookbook:
From EC2 dashboard and select Launch Instance. I selected Amazon Linux 2 AMI 64 bit ARM t4g.micro.
Once SSH access has been established, install docker support:
sudo yum update -y
sudo amazon-linux-extras install docker
sudo usermod -a -G docker ec2-user
sudo service docker start
Attempting to run the image without qualification fails since there is no 64 bit image
$ docker run --rm tardate/armi
Unable to find image 'tardate/armi:latest' locally
latest: Pulling from tardate/armi
docker: no matching manifest for linux/arm64/v8 in the manifest list entries.
See 'docker run --help'.
However, by explicitly specifying arm v7 (32 bit) I am able to run the image:
$ docker run --platform=linux/arm/v7 --rm tardate/armi
Unable to find image 'tardate/armi:latest' locally
latest: Pulling from tardate/armi
... etc
Hello, my architecture is Linux buildkitsandbox 4.19.76-linuxkit #1 SMP Tue May 26 11:42:35 UTC 2020 armv7l Linux
