To create a fresh builder host:  (should only be needed once)

Create a new Scaleway server with type "Docker 1.5" (second tab).

Make a tmpfs:
# echo "tmpfs /tmpfs tmpfs" >> /etc/fstab
# mkdir /tmpfs

Make a 2GB swap file:
# dd if=/dev/zero of=/swap count=2097152 obs=1024
# mkswap /swap
# chmod 0600 /swap
# echo "/swap none swap loop 0 0" >> /etc/fstab

Reboot.

Should see swaps in "cat /proc/swaps" and tmpfs in "cat /proc/mounts" now.

* Copy the contents of this directory to the server.

* Go into that directory and:
  # docker build -t buildlet .

Add to /etc/rc.local:

  (mkdir -p /tmpfs/buildertmp && docker run -e BUILDKEY_ARM=xxx -e BUILDKEY_ARM5=xxx -v=/tmpfs/buildertmp:/tmp --restart=always -d --name=buildlet buildlet) &
  sleep 5

.. before the exit 0

Power it down (with ARCHIVE),

Snapshot the disk.

Start a bunch of them. (see golang.org/x/build/cmd/scaleway)