Look Ma, no keyboard, no screen!
This is an overlay for Alpine Linux to enable headless installation on Raspberry Pi. There was some previous effort to achieve this purpose, but the proposed solution felt a bit hacky. So here is a cleaner way.
At the time of writing, the af_packet kernel module is missing in the initramfs. There are a couple of related issues and even a fix, but it does not seem to have found its way into a recent release. If you are using Alpine in diskless mode, DHCP will not work, and you will need to provide a static IP address.
Tested on a Raspberry Pi 2B.
Edit etc/network/interfaces and/or etc/network/wpa_supplicant/wpa_supplicant.conf to match your needs.
Build the overlay with ./make.sh and just copy the resulting tarball at the root of your SD card.
Login via SSH with user root and no password, and run setup-alpine as usual.