I am sorry for proprietary tag - I hope it helps to narrow down the scope of this mail. Tags in order generic to more specific. Hello, If I only understand the term "cloud controller" properly these are those OpenStack services which collectively control whole cloud, inclusively those services exposed to cloud user. Cloud control can run on single hosting node, or can be distributed to a group of nodes. Please correct me if I am wrong. My role is on cloud operative side (a learner to become OS user). Architecture Guide, chapter as in this mail subject states following "It’s also possible to use virtual machines for all or some of the services that the cloud controller manages, such as the message queuing. In this guide, we assume that all services are running directly on the cloud controller." It is hard to continue the lecture of this Guide due to unclear description at following points. 1. reg. "all services are running directly on the cloud controller" Can't actually understand this statement. The "on" suggests cloud controller be hosting services in mind. Furthermore, cloud controller includes only those services acting under the goal of cloud control. Service whose major purpose is to provide functionality to cloud user won't, I suppose, be part of cloud controller. Hence, this statement might be more generic as it should be. 2. reg. "use virtual machines for all or some of the services that the cloud controller manages, such as the message queuing" Will cloud controller really mange message queuing instead of include comprise it? Which use of virtual machine exactly is meant here * placing services to virtual machine during O.S. deployment to hosting IT * the IT hosting OpenStack-based cloud? Should the former bullet apply, wasn't is said in some other Guide, abstraction level rather high, that use of virtual machines as cloud host is recommended only for test and evaluation purposes?