65 lines
2.9 KiB
ReStructuredText
65 lines
2.9 KiB
ReStructuredText
..
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Copyright 2010-2011 United States Government as represented by the
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Administrator of the National Aeronautics and Space Administration.
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All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License"); you may
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not use this file except in compliance with the License. You may obtain
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a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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License for the specific language governing permissions and limitations
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under the License.
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Nova System Architecture
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========================
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Nova is comprised of multiple server processes, each performing different
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functions. The user-facing interface is a REST API, while internally Nova
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components communicate via an RPC message passing mechanism.
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The API servers process REST requests, which typically involve database
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reads/writes, optionally sending RPC messages to other Nova services,
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and generating responses to the REST calls.
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RPC messaging is done via the **oslo.messaging** library,
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an abstraction on top of message queues.
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Most of the major nova components can be run on multiple servers, and have
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a `manager` that is listening for `RPC` messages.
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The one major exception is nova-compute, where a single process runs on the
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hypervisor it is managing (except when using the VMware or Ironic drivers).
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The manager also, optionally, has periodic tasks.
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For more details on our `RPC` system, please see: :doc:`rpc`
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Nova also uses a central database that is (logically) shared between all
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components. However, to aid upgrade, the DB is accessed through an object
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layer that ensures an upgraded control plane can still communicate with
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a nova-compute running the previous release.
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To make this possible nova-compute proxies DB requests over `RPC` to a
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central manager called `nova-conductor`
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To horizontally expand Nova deployments, we have a deployment sharding
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concept called cells. For more information please see: :doc:`cells`
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Components
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----------
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Below you will find a helpful explanation of the key components
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of a typical (non-cells v1) Nova deployment.
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.. image:: ./images/architecture.svg
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:width: 100%
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* DB: sql database for data storage.
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* API: component that receives HTTP requests, converts commands and communicates with other components via the **oslo.messaging** queue or HTTP
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* Scheduler: decides which host gets each instance
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* Network: manages ip forwarding, bridges, and vlans
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* Compute: manages communication with hypervisor and virtual machines.
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* Conductor: handles requests that need coordination(build/resize), acts as a
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database proxy, or handles object conversions.
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While all services are designed to be horizontally scalable, you should have significantly more computes then anything else.
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