Rabbit - Error: mnesia_unexpectedly_running

You need to copy the cookie from the node you trying to connect

1. Let us use an example with 2 nodes: rabbit@node1 and rabbit@node2
2. Go to rabbit@node1 and copy the cookie from cat /var/lib/rabbitmq/.erlang.cookie
3. Go to rabbit@node2 remove the current cookie and paste the new one.

Execute the following commands on the same node

/usr/sbin/rabbitmqctl stop_app
/usr/sbin/rabbitmqctl reset
/usr/sbin/rabbitmqctl cluster rabbit@node1