Quorum Queues: Migrating Small Applications from Classic Mirrored Queues in RabbitMQ 3.9 Without Downtime

Goal

Achieve a zero‑downtime migration of a small application that currently uses Classic mirrored queues to Quorum Queues in a RabbitMQ 3.9+ cluster.

Constraints and Uncertainty

The migration requires a dual‑publish bridge where producers write to both queue types during cutover, introducing possible message duplication and increased latency. The performance trade‑off between Quorum Queue’s strong consistency and Classic queue’s lower latency remains an unresolved behavior for many users, affecting the decision on how long to run the bridge and when to switch traffic.

• What is the optimal duration for the dual‑publish phase that limits duplication risk while keeping latency acceptable?
• How should the application detect and deduplicate messages that may appear in both queues during the cutover to preserve exactly‑once processing?
• When should traffic be switched entirely to the Quorum Queue to guarantee consistency without causing a noticeable pause?