only insert qemu binary if building for arm

core/admin/Dockerfile

@@ -1,5 +1,7 @@
 # First stage to build assets
-FROM node:8 as assets
+ARG ARCH=""
+FROM ${ARCH}node:8 as assets
+COPY --from=balenalib/rpi-alpine:3.10 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
 
 COPY package.json ./
 RUN npm install
@@ -42,4 +44,3 @@ ENV FLASK_APP mailu
 CMD /start.py
 
 HEALTHCHECK CMD curl -f -L http://localhost/ui/login?next=ui.index || exit 1
-

tests/build_arm.sh

@@ -3,11 +3,13 @@
 ALPINE_VER="3.10"
 DISTRO="balenalib/rpi-alpine:$ALPINE_VER"
 # Used for webmails
-PHP="arm32v7/php:7.3-apache"
+QEMU="arm"
+ARCH="arm32v7/"
 
 # use qemu-*-static from docker container
 docker run --rm --privileged multiarch/qemu-user-static:register 
 docker-compose -f build.yml build \
   --build-arg DISTRO=$DISTRO \
-  --build-arg PHP_DISTRO=$PHP \
+  --build-arg ARCH=$ARCH \
+  --build-arg QEMU=$QEMU \
   --parallel $@

webmails/rainloop/Dockerfile

@@ -1,5 +1,13 @@
-ARG PHP_DISTRO=php:7.3-apache
-FROM $PHP_DISTRO
+ARG ARCH=""
+ARG QEMU=other
+
+# NOTE: only add file if building for arm
+FROM ${ARCH}php:7.3-apache as build_arm
+ONBUILD COPY --from=balenalib/rpi-alpine:3.10 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
+
+FROM ${ARCH}php:7.3-apache as build_other
+
+FROM build_${QEMU}
 #Shared layer between rainloop and roundcube
 RUN apt-get update && apt-get install -y \
   python3 curl python3-pip git \

webmails/roundcube/Dockerfile

@@ -1,5 +1,10 @@
-ARG PHP_DISTRO=php:7.3-apache
-FROM PHP_DISTRO
+# NOTE: only add file if building for arm
+FROM ${ARCH}php:7.3-apache as build_arm
+ONBUILD COPY --from=balenalib/rpi-alpine:3.10 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
+
+FROM ${ARCH}php:7.3-apache as build_other
+
+FROM build_${QEMU}
 #Shared layer between rainloop and roundcube
 RUN apt-get update && apt-get install -y \
   python3 curl python3-pip git \