How to get docker architecture, like amd64, arm32v7, in alpine linux?

Question

As the official docker alpine repository got multi-architecture support, How can I get the architecture name within the base image, especially in Dockerfile?

https://github.com/docker-library/official-images#architectures-other-than-amd64

Only getting the system is 32bit or 64bit is not good enough. I prefer the result to be the same as the docker architectures, like arm32v7, arm64v8, amd64, etc.

My goal is to bulid a nodejs docker image. For amd64, most dependences are available directly, while for some other architectures, they need to be compiled from source, in which case extra deps like python, gcc/g++ are required. I wish my script in dockerfile can figure it out and only install these extra deps only when necessary.

Answer 1

Image recipes for different architectures have their own Dockerfiles, so it's just a matter of picking the right one to work with (hope I got your question right).

There are available Node images for Alpine targeting various architectures, for example:

sudo docker pull ppc64le/node:8-alpine

Is the Node.js 8.12.0 image for PPC64LE on Alpine 3.8.

Edit after clarification:

For a multiarch Dockerfile that builds differently depending on the target architecture, you could resolve arch name on runtime, by checking the result of uname -m and using shell conditionals, for example:

RUN /bin/ash -c 'set -ex && \
    ARCH=`uname -m` && \
    if [ "$ARCH" == "x86_64" ]; then \
       echo "x86_64" && \
       apk add some-package; \
    else \
       echo "unknown arch" && \
       apk add some-other-package; \
    fi'