Dockerfile cross platform TARGETARCH build not working [duplicate] - docker

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Why should there be spaces around '[' and ']' in Bash?
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This is my Dockerfile:
FROM tomcat:9
RUN apt-get update
RUN apt-get install -y iputils-ping file
ARG TARGETARCH
RUN if ["$TARGETARCH" = "amd64"]; then \
apt-get install -y libc6-i386 ; \
fi
WORKDIR /usr/local/tomcat
... // skipped
The problem is the libc6-i386 package. It just cannot be installed on amd64 architecture.
I am building docker images on my Mac M2 machine (not sure if this is the problem), with this command:
docker buildx build --platform linux/amd64,linux/arm64 --push -t foobar .
It can successfully build 2 architecture images, but amd64 passes libc6-i386 package.
I tried to direct assign linux/amd64:
docker buildx build --platform linux/amd64 -t foobar .
And I can see the output:
[+] Building 26.1s (15/15) FINISHED
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 3.37kB 0.0s
=> [internal] load metadata for docker.io/library/tomcat:9 1.8s
=> [auth] library/tomcat:pull token for registry-1.docker.io 0.0s
=> CACHED [ 1/10] FROM docker.io/library/tomcat:9#sha256:39cb3ef7ca9... 0.0s
=> => resolve docker.io/library/tomcat:9#sha256:39cb3ef7ca9005... 0.0s
=> [internal] load build context 0.0s
=> => transferring context: 7.51kB 0.0s
=> [ 2/10] RUN apt-get update 14.7s
=> [ 3/10] RUN apt-get install -y iputils-ping file 8.7s
=> [ 4/10] RUN if ["amd64" = "amd64"]; then apt-get install -y libc6-i386 ; fi 0.1s
=> [ 5/10] WORKDIR /usr/local/tomcat
It is already comparing "amd64" = "amd64", but why doesn't it install libc6-i386 package?
Environments:
docker version
Client:
Cloud integration: v1.0.29
Version: 20.10.21
API version: 1.41
Go version: go1.18.7
Git commit: baeda1f
Built: Tue Oct 25 18:01:18 2022
OS/Arch: darwin/arm64
Context: default
Experimental: true
Server: Docker Desktop 4.15.0 (93002)
Engine:
Version: 20.10.21
API version: 1.41 (minimum version 1.12)
Go version: go1.18.7
Git commit: 3056208
Built: Tue Oct 25 17:59:41 2022
OS/Arch: linux/arm64
Experimental: false
containerd:
Version: 1.6.10
GitCommit: 770bd0108c32f3fb5c73ae1264f7e503fe7b2661
runc:
Version: 1.1.4
GitCommit: v1.1.4-0-g5fd4c4d
docker-init:
Version: 0.19.0
GitCommit: de40ad0
docker buildx version
github.com/docker/buildx v0.9.1 ed00243a0ce2a0aee75311b06e32d33b44729689
What's the problem here?

Answer 1

I think it's related to space.
When I try to run this command and got this error:
$ if ["amd64" = "amd64"]; then echo hi ; fi
[amd64: command not found
I change it to this command with 2 more space and works
$ if [ "amd64" = "amd64" ]; then echo hi ; fi
hi
So you should change your script to:
RUN if [ "$TARGETARCH" = "amd64" ]; then \
apt-get install -y libc6-i386 ; \
fi