Update Gitlab CE from 8.0.3 to 9.4.3


We use Gitlab CE version 8.0.3 in our production environment. We installed it in a Centos7 virtual machine using an omnibus package.

We want to update it by passing it to the latest version of gitlab (version 9.4.3) and restore the data from the 8.0.3 version.

At the same time we want to install the new gitlab on a docker container hosted in a virtual machine other than the one on which the production gitlab is installed.
The problem facing us is:
How do I migrate with minimal downtime? Is it possible to switch directly from version 8.0.3 to version 9.4.3? How can we restore application data (projects, users, groups, etc.) in our new gitlab with a higher version?

NB: We tried to backup the data from our gitlab which runs in production and restore them in a containerized gitlab 9.4.3 using gitlab-rake, but we have an error message saying that it is impossible to restore 8.0.3 data In a 9.4.3 gitlab.

Thanks for answers.