Is it really necessary to copy the containers themselves? Do they contain long-lasting state? (And if they do, how does this state get properly synchronized bet

Is it really necessary to copy the containers themselves? Do they contain long-lasting state? (And if they do, how does this state get properly synchronized between master and slaves?) If the offline server farms hosted a private Docker registry (which is very simple to set up), couldn't you then simply push the container images to the registry, copy the relevant YAML files, and instantiate an identical cluster that way?