For i/o intensive Docker builds, you may want to configure Docker to use memory backed storage for images and containers. Ephemeral storage has several applications, but in this case our Docker engine is on a temporary EC2 spot instance and participating in a continuous delivery pipeline. In other words, it’s ok to loose the instance and all of the Docker images it has on it. This is for a systemd based system, in this case Ubuntu 16.04.
Create the tmpfs, then reconfigure the Docker systemd unit to use it:
mount -t tmpfs -o size=25G tmpfs /mnt/docker-tmp
sed -i 's|/mnt/docker|/mnt/docker-tmp|' /etc/systemd/system/docker.service.d/docker-startup.conf
systemctl restart docker
This could be part of a bootstrapping script for build instances, or more effectively translated into config management or rolled into an AMI.