To install docker on a host you have to put it into that group in
inventory now, instead of adding the role to each host playbook. Idea
is to extend the group docker_host playbook by more docker related
things as for example metrics and monitoring.
There seem to be compatibility issues with container updates within the
same tag. These updates happen every time we run Ansible and are usually
desired, as they can fix security issues (esp. in the base image).
However, if the update cannot be trusted to run without manual intervention,
we have to pin the version and check for updates manually.
Docker does not take the tzdata from host systems, so the
timezone needs to be set individually.
Otherwise dates without explicit timezone information or Z will
be generated or interpreted in the wrong timezone
(such as dokuwiki signatures)
