RabbitMQ: high watermark has been exceeded
The RabbitMQ server detects the total amount of RAM installed on startup. By default, when the RabbitMQ server uses above 40% of the installed RAM, it raises a memory alarm and blocks all connections. Once the memory alarm has cleared (e.g. due to the server paging messages to disk or delivering them to clients) normal service resumes.
If this alert is regularly triggered it is a sign that it is time to beef up the Rabbit boxes with more RAM. Alternatively, if you don’t care about messages, you can try to purge messages or remove unused queues.
Further information can be found in the RabbitMQ docs