Nova’s Cloud Fabric is composed of the following major components:
At the heart of the cloud framework is an API Server. This API Server makes command and control of the hypervisor, storage, and networking programmatically available to users in realization of the definition of cloud computing.
The API endpoints are basic http web services which handle authentication, authorization, and basic command and control functions using various API interfaces under the Amazon, Rackspace, and related models. This enables API compatibility with multiple existing tool sets created for interaction with offerings from other vendors. This broad compatibility prevents vendor lock-in.
A messaging queue brokers the interaction between compute nodes (processing), volumes (block storage), the networking controllers (software which controls network infrastructure), API endpoints, the scheduler (determines which physical hardware to allocate to a virtual resource), and similar components. Communication to and from the cloud controller is by HTTP requests through multiple API endpoints.
A typical message passing event begins with the API server receiving a request from a user. The API server authenticates the user and ensures that the user is permitted to issue the subject command. Availability of objects implicated in the request is evaluated and, if available, the request is routed to the queuing engine for the relevant workers. Workers continually listen to the queue based on their role, and occasionally their type hostname. When such listening produces a work request, the worker takes assignment of the task and begins its execution. Upon completion, a response is dispatched to the queue which is received by the API server and relayed to the originating user. Database entries are queried, added, or removed as necessary throughout the process.
Compute workers manage computing instances on host machines. Through the API, commands are dispatched to compute workers to:
The Network Controller manages the networking resources on host machines. The API server dispatches commands through the message queue, which are subsequently processed by Network Controllers. Specific operations include:
Volume Workers interact with iSCSI storage to manage LVM-based instance volumes. Specific functions include:
Volumes may easily be transferred between instances, but may be attached to only a single instance at a time.
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