Online migration is when we while deploying the snapshot migrate from previous snapshots to the new snapsht, Offline migration is needed when the amount of changes from the old snapshot to the new snapshot are significant that online migration will not work. Its not a documented way but can be achieved by using REST APIs to get the data from the old instances and tansfer them to new instances by creating the new instance, moving the token to the desired step and updating the business data from the old instances.