[dilatedmind]

for this specific example, I think the shared library is not the correct approach. Queues work for simple fifo behavior, but in this case they also need fairness (and perhaps other logic, like rate limiting per client, different priority for certain clients etc)

For example, "Customer-A is clogging up the work queue and starving other customers out". The solution to this could look something like linux's completely fair scheduler, where every client is allocated some amount of messages per interval of time. This means messages need to be processed in a different order then they are enqueued, and queues are not good at reordering messages.

I would suggest implementing the queue abstraction as a rest or grpc service, backed by a database like postgres, which holds message payloads and everything related to message state (in progress, retry after times, etc). Now we can implement all the necessary scheduling logic within our queue service.