OpenStack is an open source Apache 2.0 licensed framework used to build cloud platforms. It is primarily an IaaS and has been in the developer community since 2010. The OpenStack Foundation manages the software and has support from more than 500 companies, including Intel, IBM, Red Hat, and Ericsson. We will use OpenStack as a reference architecture for other cloud providers as much of the components and terminology are reused in commercial clouds. 

OpenStack started as a joint project between NASA and Rackspace around 2010. The architecture has all the major components of other cloud systems, including compute and load balancing; storage components, including backup and recovery; networking components, dashboards, security and identity, data and analytics packages, deployment tools, monitors and meters, and application services. These are the components that an architect would look for when choosing a cloud service. 

Architecturally, OpenStack is an interwoven layer of components. The basic form of an OpenStack cloud is shown in the following figure. Each service has a particular function and a unique name (such as Nova). The system acts as a whole, providing a scalable enterprise-class cloud functionality:

All communication within the OpenStack components is done through Advanced Message Queueing Protocol (AMQP) message queues, specifically the RabbitMQ or Qpid. Messages can either be non-blocking or blocking depending on how the message was sent. A message would be sent as a JSON object into RabbitMQ and receivers would find and fetch their messages from the same service. This is a loosely-coupled remote procedure call (RPC) method of communication between the major subsystems. The benefit in a cloud environment is that client and server vices are completely decoupled, and this allows the servers to dynamically scale up or down. Messages are not broadcast but directed, which keeps traffic to a minimum. You may also recall that AMQP is a common messaging protocol used in the IoT space.