Launching run docker from cloud-init incorrectly prefixes "docker.io" to image name

Question

I am starting a GCE server with a cloudinit file, that calls a docker image. On startup, pulling the docker image fails, but if I run the same service upon logging in it succeeds. I would like it to work upon launch.

Looking at the service logs, it seems that it is incorrectly prefixing the docker pull with docker.io and so failing the job.

Is there something I could be doing to prevent this? Do I perhaps need to wait or check for something else to load before trying the docker pull?

Here is my cloud-init file:

#cloud-config

users:
- name: shinyuser
  uid: 2000

write_files:
- path: /etc/systemd/system/shinyserver.service
  permissions: 0644
  owner: root
  content: |
    [Unit]
    Description=Shiny server

    [Service]
    ExecStart=/usr/bin/docker run --name=vdshinyserver -p 80:3838 -v /home/shinyuser/shinyapps/:/srv/shiny-server/ -v /home/shinyuser/srv/shinylog/:/var/log/ rocker/shiny
    ExecStop=/usr/bin/docker stop vdshinyserver

runcmd:
- systemctl daemon-reload
- systemctl start shinyserver.service 

And here are the logs:

mark@xxxshiny ~ $ sudo journalctl -u shinyserver
-- Logs begin at Wed 2016-10-05 08:39:06 UTC, end at Wed 2016-10-05 08:39:46 UTC. --
Oct 05 08:39:11 xxxshiny docker[1016]: Unable to find image 'rocker/shiny:latest' locally
Oct 05 08:39:26 xxxshiny docker[1016]: Pulling repository docker.io/rocker/shiny
Oct 05 08:39:31 xxxshiny docker[1016]: /usr/bin/docker: Tag latest not found in repository docker.io/rocker/shiny.
Oct 05 08:39:31 xxxshiny docker[1016]: See '/usr/bin/docker run --help'.
Oct 05 08:39:31 xxxshiny docker[1045]: Error response from daemon: No such container: vdshinyserver

mark@visit-dubai-shiny ~ $ sudo systemctl start shinyserver.service
mark@visit-dubai-shiny ~ $ sudo journalctl -u shinyserver
...
Oct 05 08:42:22 xxxshiny docker[1117]: Unable to find image 'rocker/shiny:latest' locally
Oct 05 08:42:23 xxxshiny docker[1117]: latest: Pulling from rocker/shiny
Oct 05 08:42:23 xxxshiny docker[1117]: a84f66826a7f: Pulling fs layer
Oct 05 08:42:23 xxxshiny docker[1117]: aaf7c0da390d: Pulling fs layer
...etc...

Answer 1

I edited my cloudinit to match that at the Docker documentation to include a requirement of docker.service in the file, and it now works:

#cloud-config

users:
- name: shinyuser
  uid: 2000

write_files:
- path: /etc/systemd/system/shinyserver.service
  permissions: 0644
  owner: root
  content: |
    [Unit]
    Description=VisitDubai Shiny server for reporting
    Requires=docker.service
    After=docker.service

    [Service]
    Restart=always
    ExecStart=/usr/bin/docker run --name=vdshinyserver -p 80:3838 -v /home/shinyuser/shinyapps/:/srv/shiny-server/ -v /home/shinyuser/srv/shinylog/:/var/log/ rocker/shiny
    ExecStop=/usr/bin/docker stop vdshinyserver