We use haveged to provide entropy on CoreOS servers lacking other suitable sources.
Starting a container from this image is simple.
docker run --name haveged --privileged storytel/haveged
On CoreOS we run this as a Systemd service.
[Unit]
Description=haveged
Requires=docker.service
After=docker.service
[Service]
Restart=always
ExecStartPre=/usr/bin/docker pull storytel/haveged
ExecStartPre=-/usr/bin/docker rm -f haveged
ExecStart=/usr/bin/docker run --name haveged --privileged storytel/haveged
ExecStop=/usr/bin/docker stop haveged
TimeoutStartSec=1m
[Install]
WantedBy=multi-user.target