Crosscompile go(lang) app with docker for alpine linux (musl) aarch64 with native libs so CGO enabled

## Background I'm writing an open-source GTK go app subsonic API client which: - targets on first place mobile friendly Linux like postmarketOS (alpine linux), Mobian (debian) - in future will be also extended to desktop Linux, Windows and Mac OS but not Android or iOS as they already have one. - needs to be available at least on aarch64 and x86_64 - depends on native libs like portaudio, libasound, libopus - so it needs CGO to be enabled I haven't published app yet as I self-host my git and I have to do some additional config. It won't be available until late october 2021. App successfully compiles (on host) and runs on my main PC which is x86_64 fedora. App successfully compiles (on docker) and runs on aarch64 **glibc** distros like Mobian This is Dockerfile:

`
FROM golang:1.17-bullseye
LABEL os=linux
LABEL arch=arm64
ENV GOOS=linux
ENV GOARCH=arm64
ENV CGO_ENABLED=1
ENV CC=aarch64-linux-gnu-gcc
ENV PATH="/go/bin/${GOOS}_${GOARCH}:${PATH}"
ENV PKG_CONFIG_PATH=/usr/lib/aarch64-linux-gnu/pkgconfig
# install build & runtime dependencies
RUN dpkg --add-architecture arm64 
RUN apt update && apt upgrade -y 
RUN apt install -y --no-install-recommends \
        protobuf-compiler \
        upx \
        gcc-aarch64-linux-gnu \
        libc6-dev-arm64-cross \
        pkg-config \
        libasound2-dev:arm64 \
    	libgtk-3-dev:arm64 \
    	libcairo2-dev:arm64 \
    	libglib2.0-dev:arm64 \
    	libgdk-pixbuf2.0-dev:arm64 \
        libsamplerate0:arm64 \
        libsamplerate0-dev:arm64 \
        libopusfile0:arm64 \
        libopusfile-dev:arm64 \
        libopus0:arm64 \
        libopus-dev:arm64 \
        libportaudio2:arm64 \
        portaudio19-dev:arm64 
# install build dependencies (code generators)
RUN go get github.com/hajimehoshi/oto \
    && go get github.com/faiface/beep \
    && go get github.com/faiface/beep/flac \
    && go get github.com/faiface/beep/speaker \
    && go get github.com/faiface/beep/mp3 \
    && go get github.com/faiface/beep/vorbis \
    && go get github.com/faiface/beep/wav\
    && go get github.com/gotk3/gotk3 \
    && go get github.com/delucks/go-subsonic \
    && go get github.com/hashicorp/go-retryablehttp \
    && go get github.com/zalando/go-keyring \
    && go get github.com/emirpasic/gods/lists/ \
    && go get github.com/emirpasic/gods/lists/arraylist \

` ## Problems 1. I can't run Mobian working binary on postmarketOS as alpine linux uses musl instead. file output is: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, (...) for GNU/Linux 3.7.0. not stripped. 2. I haven't manged to use musl toolchain in docker debian as it is 32 binary executable and image is 64 bit. 3. I couldn't find anything about multiarch in alpine so probably I can't use docker image goalng:1.17-alpine on x86_64 (I'd have also to find native libs packaged) I wish it's just problem with my config, if it's possible I'd love solution with docker as I'd like to use CI/CD in future. ## Resources, ideas, workarounds - I have raspberry pi with debian installed with some services. I could use with native musl toolchain and debian aarch64 docker container but it's not handy in production pipeline. Also, I haven't tried this. ## Good to read 1. Crosscompile CGO projects (also with docker) 2. Crosscompile with cross-platform musl toolchains 3. Related stackoverflow thread about alpine linux and go binaries