Data volume shared by two containers
The volume frab_data is shared by the live and stage instances of frab:
$ dokku volume:list:apps frab_data dbp2016-live frab-stage
Although this is possible and useful in some cases, there is a potential risk for data corruption/loss, especially as both containers will be operating on the same files. From the docker documentation:
Multiple containers can also share one or more data volumes. However, multiple containers writing to a single shared volume can cause data corruption. Make sure your applications are designed to write to shared data stores.
I propose these are decoupled for risk mitigation and, if @ponder needs update data files for staging, the volumes can simply be rsync'd.