Multi-arch build using `--platform` and `--build-arg`

[yellowmamba]

Hi there,

I'm having some confusion around using --build-arg in conjunction with --platform. Here's an example of Dockerfile

ARG ARCH
RUN curl "https://awscli.amazonaws.com/awscli-exe-linux-${ARCH}.zip" -o "awscliv2.zip" \

When I build for amd64 and arm64, I do this

docker buildx build --platform=linux/amd64,linux/arm64 --build-arg ARCH=x86_64,aarch64 -t my-multi-arch-image .

The result of the curl command is either platform is

RUN curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64,aarch64.zip" -o "awscliv2.zip"

According to docs,

--build-arg stringArray
--platform stringArray

I thought they both use comma-separated syntax, am I understanding it incorrectly?

[morlay]

Here real world example

You could use case $(uname -m) to define the correct file.
https://github.com/istio/tools/blob/master/docker/build-tools/Dockerfile#L265-L271

or just use the platform build arg TARGETARCH:
https://github.com/istio/tools/blob/master/docker/build-tools/Dockerfile#L691

no need to pass another build arg for arch or platform

[yellowmamba]

Yeah I am not a big fan of having conditional logic in Dockerfile. TARGETARCH unfortunately does not return the exact value I need in my RUN command. I'm more looking for a successful example of using --build-arg alongside --platform as documented in buildx.

[crazy-max]

@yellowmamba #717 (comment)

[morlay]

TARGETARCH unfortunately does not return the exact value I need in my RUN command

have to use case ${TARGETARCH} in RUN of Dockerfile.

--build-arg only support pass same value for different platforms now.

[crazy-max]

https://pkg.go.dev/github.com/spf13/pflag#StringArray

StringArray defines a string flag with specified name, default value, and usage string. The return value is the address of a []string variable that stores the value of the flag. The value of each argument will not try to be separated by comma. Use a StringSlice for that.

https://pkg.go.dev/github.com/spf13/pflag#StringSlice

StringSlice defines a string flag with specified name, default value, and usage string. The return value is the address of a []string variable that stores the value of the flag. Compared to StringArray flags, StringSlice flags take comma-separated value as arguments and split them accordingly. For example:

--ss="v1,v2" --ss="v3"

will result in

[]string{"v1", "v2", "v3"}

[morlay]

@crazy-max I think he just want this for different platforms.

# TARTETARCH=amd64
RUN curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o "awscliv2.zip"

# TARTETARCH=arm64
RUN curl "https://awscli.amazonaws.com/awscli-exe-linux-aarch64.zip" -o "awscliv2.zip"

In this case, could be simple without --build-arg

RUN curl "https://awscli.amazonaws.com/awscli-exe-linux-$(uname -m).zip" -o "awscliv2.zip"

[crazy-max]

@morlay Yes exactly TARGETARCH is the way to go if the arch matches the one in the filename you want to download otherwise use case ${TARGETARCH} or case ${TARGETPLATFORM} like https://github.com/crazy-max/docker-docker/blob/782b584781cd0130798a6640c37d40476c532a10/Dockerfile-20.10#L17-L23.

[crazy-max]

Also you can simply use the official AWS CLI version 2 Docker image:

COPY --from=amazon/aws-cli /usr/local/aws-cli /usr/local/aws-cli
COPY --from=amazon/aws-cli /usr/local/bin/aws /usr/local/bin/aws