Users that upgrade to PuppetDB could still have commands sitting in ActiveMQ. Those commands need to be enqueued into the new queuing system when upgraded. The current thinking is that this would be a background thread that is created on startup, looks for the ActiveMQ directory and receives and messages (when present) and just enqueues them into the new queue and commits them. Once all messages have been consumed, we can delete the queue or something similar as an indication that we no longer need to check for messages in the queue.