Here is the error message; Please explain in layman's terms why this is happening and how to fix. Thanks. (But Horizon seems to work as usual - so I am confused if the setup is good or not)

ERROR : Error appeared during Puppet run: 192.168.0.201_controller.pp
Error: Systemd start for rabbitmq-server failed!
You will find full trace in log /var/tmp/packstack/20170617-192203-xo8a4u/manifests/192.168.0.201_controller.pp.log

Here is the log;

[mNotice: /Stage[main]/Rabbitmq::Install/Package[rabbitmq-server]/ensure: created
Notice: /Stage[main]/Rabbitmq::Config/File[/etc/rabbitmq]/owner: owner changed 'rabbitmq' to 'root'
Notice: /Stage[main]/Rabbitmq::Config/File[/etc/rabbitmq]/group: group changed 'rabbitmq' to 'root'
Notice: /Stage[main]/Rabbitmq::Config/File[/etc/rabbitmq/ssl]/ensure: created
Notice: /Stage[main]/Rabbitmq::Config/File[rabbitmq.config]/content: content changed '{md5}c8e444b74c6294006936abdaea55a079' to '{md5}54e1c4e776fd87d974a4ce52a80720fa'
Notice: /Stage[main]/Rabbitmq::Config/File[rabbitmq.config]/mode: mode changed '0644' to '0640'
Notice: /Stage[main]/Rabbitmq::Config/File[rabbitmq-env.config]/ensure: defined content as '{md5}d1faed99ee5f85f2e3ef458c2d19f3a8'
Notice: /Stage[main]/Rabbitmq::Config/File[/etc/systemd/system/rabbitmq-server.service.d]/ensure: created
Notice: /Stage[main]/Rabbitmq::Config/File[/etc/systemd/system/rabbitmq-server.service.d/limits.conf]/ensure: defined content as '{md5}8eb9ff6c576b9869944215af3a568c2e'
Notice: /Stage[main]/Rabbitmq::Config/Exec[rabbitmq-systemd-reload]: Triggered 'refresh' from 1 events
Notice: /Stage[main]/Rabbitmq::Config/File[/etc/security/limits.d/rabbitmq-server.conf]/ensure: defined content as '{md5}5ddc6ba5fcaeddd5b1565e5adfda5236'
Error: Systemd start for rabbitmq-server failed!
journalctl log for rabbitmq-server:
-- Logs begin at Sat 2017-06-17 19:00:56 EDT, end at Sat 2017-06-17 19:34:12 EDT. --
Jun 17 19:34:10 <my_domain_name> systemd[1]: Starting RabbitMQ broker...
Jun 17 19:34:11 <my_domain_name> rabbitmq-server[18966]: ERROR: epmd error for host tryopenstack: address (cannot connect to host/port)
Jun 17 19:34:11 <my_domain_name> systemd[1]: rabbitmq-server.service: main process exited, code=exited, status=1/FAILURE
Jun 17 19:34:12 <my_domain_name> rabbitmqctl[19062]: Stopping and halting node rabbit@tryopenstack ...
Jun 17 19:34:12 <my_domain_name> rabbitmqctl[19062]: Error: unable to connect to node rabbit@tryopenstack: nodedown
Jun 17 19:34:12 <my_domain_name> rabbitmqctl[19062]: DIAGNOSTICS
Jun 17 19:34:12 <my_domain_name> rabbitmqctl[19062]: ===========
Jun 17 19:34:12 <my_domain_name> systemd[1]: Failed to start RabbitMQ broker.
Jun 17 19:34:12 <my_domain_name> systemd[1]: Unit rabbitmq-server.service entered failed state.
Jun 17 19:34:12 <my_domain_name> systemd[1]: rabbitmq-server.service failed.

Error: /Stage[main]/Rabbitmq::Service/Service[rabbitmq-server]/ensure: change from stopped to running failed: Systemd start for rabbitmq-server failed!
journalctl log for rabbitmq-server:
-- Logs begin at Sat 2017-06-17 19:00:56 EDT, end at Sat 2017-06-17 19:34:12 EDT. --
Jun 17 19:34:10 <my_domain_name> systemd[1]: Starting RabbitMQ broker...
Jun 17 19:34:11 <my_domain_name> rabbitmq-server[18966]: ERROR: epmd error for host tryopenstack: address (cannot connect to host/port)
Jun 17 19:34:11 <my_domain_name> systemd[1]: rabbitmq-server.service: main process exited, code=exited, status=1/FAILURE
Jun 17 ...