Docker pull error in systemd script on CoreOS

I created a droplet with the following configuration:

512MB Ram 20GB SSD Disk Amsterdam 3 CoreOS CoreOS (beta) 494.0.0

CoreOS was subsequently updated to 494.1.0.

Since I don’t need a cluster, I didn’t provide a cloud-config.

Then I added the following systemd script in /etc/systemd/system/hello.service (copied from the official CoreOS tutorial):

[Unit]
Description=MyApp
After=docker.service
Requires=docker.service

[Service]
TimeoutStartSec=0
ExecStartPre=-/usr/bin/docker kill busybox1
ExecStartPre=-/usr/bin/docker rm busybox1
ExecStartPre=/usr/bin/docker pull busybox
ExecStart=/usr/bin/docker run --name busybox1 busybox /bin/sh -c "while true; do echo Hello World; sleep 1; done"

[Install]
WantedBy=multi-user.target

I ran ‘sudo systemctl enable hello’ and ‘sudo systemctl start hello’. Everything worked perfectly.

Then I rebooted the machine, and this happened:

systemd[1]: Starting MyApp...
docker[478]: busybox1
docker[600]: busybox1
docker[610]: Pulling repository busybox
docker[610]: Get https://index.docker.io/v1/repositories/library/busybox/images: dial tcp: lookup index.docker.io: connection refused
systemd[1]: hello.service: control process exited, code=exited status=1
systemd[1]: Failed to start MyApp.
systemd[1]: Unit hello.service entered failed state.

I destroyed and recreated the droplet, with exactly the same result.

I tried the same approach and script locally with Vagrant as well as on Google Computing Engine, and it worked as expected both times.

Am I doing something wrong, or does the problem lie with Digital Ocean?