There are a dozen good reasons to get off of ActiveMQ, but primarily that it's a huge, flaming bag of SPOF. This task is complete once ActiveMQ is uninstalled everywhere, and the replacement system is high-availability or at least redundant.
Must complete this work before roughly the end of August, in order to leave time to stabilize ahead of Big English.
We've done a lot of the groundwork already by wrapping php-queue under the DonationQueue module in DonationInterface, so the work here is mostly in generalizing, applying to the remaining components, and then deploying the thing.
* Producers will begin mirroring messages to both ActiveMQ and the new queue. Messages will be set to expire in a month or less, so intermittent failures while we start the new consumers are fine.
* Incrementally switch queue consumers to consume via Kafka, beginning with the non-critical queues and tools. Keep an eye on queue usage and set the old message archiver to dump legacy data if storage issues arise.
* Deactivate each mirror to ActiveMQ and finally retire the box only once we're 100% certain about the new stuff.