Message queuing services facilitate inter-process communication in OpenStack. OpenStack supports these message queuing service back ends: RabbitMQ Qpid ZeroMQ or 0MQ Both RabbitMQ and Qpid are Advanced Message Queuing Protocol (AMQP) frameworks, which provide message queues for peer-to-peer communication. Queue implementations are typically deployed as a centralized or decentralized pool of queue servers. ZeroMQ provides direct peer-to-peer communication through TCP sockets. Message queues effectively facilitate command and control functions across OpenStack deployments. Once access to the queue is permitted no further authorization checks are performed. Services accessible through the queue do validate the contexts and tokens within the actual message payload. However, you must note the expiration date of the token because tokens are potentially re-playable and can authorize other services in the infrastructure. OpenStack does not support message-level confidence, such as message signing. Consequently, you must secure and authenticate the message transport itself. For high-availability (HA) configurations, you must perform queue-to-queue authentication and encryption. With ZeroMQ messaging, IPC sockets are used on individual machines. Because these sockets are vulnerable to attack, ensure that the cloud operator has secured them.