When you have hosts with multiple interfaces that you want them to be parts of a RabbitMQ cluster, you may get this error:

Error: {cannot_discover_cluster,"The nodes provided are either offline or not running"}

This may happen when you want all communication to go through a specific interface for each host. In such cases after setting up the DNS and/or /etc/hosts correctly, it may help you to explicitly set RABBITMQ_NODE_IP_ADDRESS and RABBITMQ_NODENAME in /etc/rabbitmq/rabbitmq-env.conf.

Then you may proceed with the rest of the instructions.