How to set Architecture for docker build to arm64? - docker

Question

I have a Dockerfile that I run on amd64 but want to run on arm64. Since go build tool takes GOARCH=arm64 as argument I don't need any other cross compilation tool to make the binary.
# Run the build
FROM mojlighetsministeriet/go-polymer-faster-build
ENV WORKDIR /go/src/github.com/mojlighetsministeriet/email
COPY . $WORKDIR
WORKDIR $WORKDIR
RUN go get -t -v ./...
RUN CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go build
# Create the final docker image
FROM scratch
COPY --from=0 /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
COPY --from=0 /go/src/github.com/mojlighetsministeriet/email/email /
ENTRYPOINT ["/email"]
The problem is that the resulting image gets marked with the wrong Architecture amd64 instead of arm64. How can I pass an argument to docker build so that it sets Architecture to arm64?
$ docker image inspect mojlighetsministeriet/email-arm64
[
{
"Id": "sha256:33bcd7da8631c7a0829d61cc53479a26ab7f31fab1cb039105de415ddc6178f3",
"RepoTags": [
"mojlighetsministeriet/email-arm64:latest"
],
"RepoDigests": [
"mojlighetsministeriet/email-arm64#sha256:ab3f05d5597c3a304953b5c14f795179aa75bdfd458af3dc3cfb8b8d8eb87bc3"
],
"Parent": "sha256:e5888262d93ea0946b5fd8146cf1c19ec3a7bac4d36eb51848ef0aefa75cf8e7",
"Comment": "",
"Created": "2017-12-05T18:36:36.273648787Z",
"Container": "7a226edb3b52aaeeefec9e0fb4dd1da50d84992fb6cc374aeda9d82eec1bb2c8",
"ContainerConfig": {
"Hostname": "7a226edb3b52",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"/bin/sh",
"-c",
"#(nop) ",
"ENTRYPOINT [\"/email\"]"
],
"Image": "sha256:e5888262d93ea0946b5fd8146cf1c19ec3a7bac4d36eb51848ef0aefa75cf8e7",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": [
"/email"
],
"OnBuild": null,
"Labels": {}
},
"DockerVersion": "17.10.0-ce",
"Author": "",
"Config": {
"Hostname": "",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": null,
"Image": "sha256:e5888262d93ea0946b5fd8146cf1c19ec3a7bac4d36eb51848ef0aefa75cf8e7",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": [
"/email"
],
"OnBuild": null,
"Labels": null
},
"Architecture": "amd64",
"Os": "linux",
"Size": 7861466,
"VirtualSize": 7861466,
"GraphDriver": {
"Data": {
"LowerDir": "/var/lib/docker/overlay2/03cb0162bf922636e4e0ec90123b81565a447c6cd511741103551d2f0e7f09f9/diff",
"MergedDir": "/var/lib/docker/overlay2/091f74815a0caf457df7e57ade43b41c4dd8551388beca44815a7038501742ee/merged",
"UpperDir": "/var/lib/docker/overlay2/091f74815a0caf457df7e57ade43b41c4dd8551388beca44815a7038501742ee/diff",
"WorkDir": "/var/lib/docker/overlay2/091f74815a0caf457df7e57ade43b41c4dd8551388beca44815a7038501742ee/work"
},
"Name": "overlay2"
},
"RootFS": {
"Type": "layers",
"Layers": [
"sha256:66f615d03920919b0fa8bc9fed45515bb95636be1837fdd10a82b2c183e2ad5b",
"sha256:bd6a01b885eb6e3eec38a3fe3a2899646509633730b210cf6987456fd40b8a1c"
]
},
"Metadata": {
"LastTagTime": "2017-12-14T10:24:10.796813522+01:00"
}
}
]

Answer 1

https://docs.docker.com/desktop/multi-arch/
# Shows builders installed
docker buildx ls
# Use builder that supports platform
docker buildx use default
docker buildx build --platform linux/arm64 -t <image_name>:<image_tag> --push .

Answer 2

For building single docker images: Set your environment variable using the command line or modifying your .bashrc or .zshenv file. (introduced in v19.03.0 in 03/2019)
export DOCKER_DEFAULT_PLATFORM=linux/arm64
Alternatively, in the Dockerfile, include the following flag in the FROM command (for a multi-stage Dockerfile build, the flag is only needed for the first stage):
FROM --platform=linux/arm64 python:3.7-alpine
For building images as part of a docker-compose build, include the platform: linux/arm64 for each service. For example:
services:
frontend:
platform: linux/arm64
build: frontend
ports:
- 80:80
depends_on:
- backend
backend:
platform: linux/arm64
build: backend
This also works the other way around, for instance if you have an Apple M1 Chip and want to deploy images to a Linux or Windows based AMD64 environment. Simply swap 'linux/arm64' for 'linux/amd64'

Answer 3

I was able to solve the problem, not exactly as I wanted, but close enough.
Have an amd64 Linux machine with docker
Setup qemu user static for arm support https://hub.docker.com/r/multiarch/qemu-user-static/
In your docker file use base image with support for arm. E.g. ubuntu
Build your image with command similar to the following:
docker build --platform arm --pull -t your_tag .
This command will force docker to pull arm version of the base image and will also set arm architecture to your result image. But be careful, if you use tags with multiple architectures, the command above will set the tag to arm version. So to run the native amd64 version you will need to pull the tag again without --platform arg.