OpenStack Terminology

Cloud Controller: -The Coordinating manager. All the machines in the OpenStacks cloud, communicate with the cloud controller using the Advanced Message Queuing Protocol(AMQP).

In Red hat OpenStack there are two option-the Apache Qpid messaging daemon(qpidd) and RabbitMQ.

Tenant or Project: - It is a group of items - users, instances, image, volume, network etc.

The term tenant is used interchangeably with project.

The term tenant is used in keystone and project is used in Horizon.

Compute node: - Machine running the Nova compute service.

Volume: -The persistent disk  attached to a instance. Volumes can be attached and detached from running instances as needed.

Ephemeral disk:- A temporary disk used by an instance .When an instance is created the ephemeral disk is created as a QCOW2 image on compute node. When instance is terminated this disk is removed.it normally appears as a /dev/vdb within the instance.

Instance :- A virtual machine. Also sometimes referred to as a VM or a guest.

Flavor:- A virtual hardware profile applied to instances at creation time.  Flavors control the number of vCPUs, memory, root disk size and ephemeral storage size of an instance.

Stack: - A group of instances built from a template.

Hypervisor: - Servers which run the instances created in your environment.

Dashboard: -The web based GUI for interacting with your cloud. The Dashboard represents a subset of the functionality available via the API and CLI.

API: - The API used for interacting with cloud/OpenStack component .  Both the Dashboard and CLI provide interfaces into the API, which is where all functionality appears first.

Floating IP: - An IP address (usually public) which is mapped to a specific instance to allow external connectivity into that instance.  

Security Group: - A collection of firewall rules applied to an instance