When a new version of Gallium Data is released, you can upgrade to it at any time simply by specifying its version when you start a Docker instance.
For instance, if you've been running with the following command:
docker run -d -p 8089:8080 galliumdata/gallium-data-engine:1.8.3-1851
and a new version of Gallium Data is released, then you can stop your Docker instance and restart it with the updated version, e.g.:
docker run -d -p 8089:8080 galliumdata/gallium-data-engine:1.8.4-1859
Your repository will be automatically upgraded if you publish it in this new version, but it will be untouched if you do not publish.
Backward compatibility is not guaranteed: a repository may not be compatible with a version of Gallium Data that is older than the version with which the repository was created or last updated.