There is no official alpine Docker image for the arm platform. The onec i found are not taking advantage of the much quicker Fastly CDN basedpackage mirror option
Here are steps to rebuild the images on a rpi:
git clone https://github.com/gliderlabs/docker-alpine.git docker-alpine-gliderlabs
cd docker-alpine-gliderlabs/
# the "builder" images has to be FROM an rpi based alpine
sed -i "/FROM/ s:.*:FROM hypriot/rpi-alpine-scratch:" builder/Dockerfile
docker build -t alpine-builder builder
# build library alpine
docker run --name alpine-build-v3.2 alpine-builder -s -t UTC -r v3.2 -m http://dl-4.alpinelinux.org/alpine > ./versions/library-3.2/rootfs.tar.gz
docker build -t alpine:latest versions/library-3.2
# build gliderlabs/alpine
docker rm alpine-build-v3.2
docker run --name alpine-build-v3.2 alpine-builder -s -c -t UTC -r v3.2 -m http://alpine.gliderlabs.com/alpine > ./versions/gliderlabs-3.2/rootfs.tar.gz
docker build -t gliderlabs/alpine:latest versions/gliderlabs-3.2
Lets see how much time is needed to install curl: 4sec instead of 15sec
$ time (docker run alpine apk add -U curl > /dev/null)
real 0m15.916s
$ time (docker run gliderlabs/alpine apk add -U curl > /dev/null)
real 0m4.225s
$ time (docker run alpine apk add -U curl > /dev/null)
0,02s user 0,01s system 0% cpu 3,376 total
$ time (docker run gliderlabs/alpine apk add -U curl > /dev/null)
0,02s user 0,01s system 0% cpu 3,503 total