As the article points out, I feel that messaging really shines when it comes to failures: Instead of an - at best - WARN or ERROR log line amongst millions of log lines, the failing message "pops out" of the messaging fabric, into a Dead Letter Queue (DLQ).

You shall obviously set up monitoring of the MQ and all its DLQs. Once you've done that, you will literally never have a failing processing flow that isn't caught. A successfully initiated Mats Flow will either run to completion, or it will DLQ. Guaranteed.

The MatsBrokerMonitor is a Mats-specific such monitor (compared to the generic monitor ActiveMQ comes with). The pages here are a bit lacking, but it at least explains a bit: https://mats3.io/docs/matsbrokermonitor/