The Rabbitmq instance on saatchi.internal.softwareheritage.org is graphed in Munin:
http://munin.internal.softwareheritage.org/internal.softwareheritage.org/saatchi.internal.softwareheritage.org/rabbitmq_messages.html

Howewer, no alert is sent when an unreasonable number of messages is in the queue.
Add an Icinga2 alert when 200K messages are being queued.