This document provides an overview of OpenStack Nova's architecture and code structure. It begins with an introduction to Nova's mission to provide scalable on-demand access to compute resources. It then covers Nova's core components, data flows, and code organization. Key aspects summarized include Nova's use of Cells to partition compute nodes, its facade design pattern for APIs, and its reliance on common OpenStack libraries like Oslo and Stevedore for configuration, logging, and extensibility.

1. OpenStack Nova ‘Reverse Engineer’
2016 May 07
Hieu LE
Vietnam OpenStack Community Organizer
Fujitsu Vietnam - PODC
Copyright 2016 Fujitsu Vietnam Limited

2. Starting Point (1)
1 Copyright 2016 Fujitsu Vietnam Limited
Video Tutorial: how to setup remote debugging environment for OpenStack Nova,
request from some community members.
Ref: https://youtu.be/Z0PmKyeZjjA

3. Starting Point (2)
 @NamNH (Fujitsu) contribute to documentation: “Debugging
OpenStack Neutron”
Ref: https://vietstack.wordpress.com/2016/04/12/how-to-remote-debugging-openstack-neutron/
Hope that he will present at next
technical meetup about Neutron ;)
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4. Agenda
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1. Architecture overview
2. Data Flows
3. Nova Code Structure Components
4. Conclusion
3

5. “to provide massively scalable, on demand,
self service access to compute resources”
OpenStack Nova mission
http://docs.openstack.org/developer/nova/project_scope.html
4 Copyright 2016 Fujitsu Vietnam Limited

6. “to provide massively scalable, on demand,
self service access to compute resources”
OpenStack Nova mission
http://docs.openstack.org/developer/nova/project_scope.html
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Virtual Servers Containers Bare Metal Servers Driver Parity

7. Agenda
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1. Architecture overview
2. Data Flows
3. Nova Code Structure Components
4. Conclusion
6

8. Architecture overview
 Model:
 Nova Network
 Neutron
 Cells (v1, 2)
 Core components
 DB: sql database for data storage.
 API: receive HTTP requests, converts commands and communicates with other
components via the oslo.messaging queue or HTTP
 Scheduler: decides which host gets each instance
 Compute: manages communication with hypervisor and virtual machines.
 Conductor: handles requests that need coordination(build/resize), acts as a
database proxy, or handles object conversions.
 Cells: used by some large deployments to partition compute nodes into smaller
groups, coupled with a database and queue. DEFAULT FROM MITAKA WITH
CELLS V2
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9. Architecture overview
 Other nova components
 Network: manages ip forwarding, bridges, and vlans
 Metadata: serves metadata for instances
 Cert: serves X509 certificates, using for euca-bundle-image and only needed for
EC2 API
 Console auth and proxies: noVNC, SPICE, XVP, RDP.. for remote console
purpose toward instances
 EC2: *DEPRECATED AND MOVE TO NEW EC2-API PROJECT FROM
MITAKA* using EC2 API with nova services.
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10. Architecture overview (1)
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1
2 3 45
7
6
Ref:
http://docs.openstack.org/developer/nova/architecture.html

11. Architecture overview (2)
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1
2 3 45
7
6
Ref:
http://docs.openstack.org/developer/nova/architecture.html

12. Architecture overview (2)
 Normal Workflow
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 MQ and DB is under heavy-load.
 Cells
There are Austin summit video about Nova scheduler performance.
https://www.openstack.org/videos/video/dive-into-nova-scheduler-performance-where-is-the-bottleneck
https://docs.google.com/presentation/d/1UG1HkEWyxPVMXseLwJ44ZDm-
ek_MPc4M65H8EiwZnWs/edit?ts=571fcdd5#slide=id.g12d2cf15cd_2_84

13. Architecture overview (3)
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Ref: OpenStack Japan User Group

14. Architecture overview (3)
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API DB
Compute DB

15. Architecture overview (3)
 Cells: aim for easily scaling and providing fault tolerance by
partition compute nodes into smaller groups with separate
database and queue, instead of legacy deployment model with
single logical database and message queue.
 Cells v1:
 Optional
 Not all features supported
 Sync instance between DBs
 Cells v2:
 Default deployment model is one v2 cell
 New API database
 Tools to migrate from cells v1 **NOT IMPLEMENTED IN MITAKA,
PLAN IS IN NEWTON**
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16. Agenda
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1. Architecture overview
2. Data Flows
3. Nova code structure
4. Conclusion
15

17. Façade
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WSGIService
oslo_service lib
Paste filters
Paste/Paste.Deploy lib via api-paste.ini
WebOb lib for WSGI req/res wrapper
1. RESTful req 2. WSGI Req
APIRouter
RoutesMiddleware
3. Filtered req
Routes lib
Extension
Controller:
index/show/delete/
create..
Extension
Controller:
index/show/delete/
create..
Extension
Controller:
index/show/delete/
create..
4. Req dispatching
stevedore lib for managing ext, ctrl
Expose via pbr entrypoint
oslo_conf
Façade/Decorator pattern
oslo_message
RPC

18. Façade design pattern
 Nova-compute API (nova/nova/compute/api.py): API, HostAPI,
InstanceActionAPI, KeypairAPI…
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Ref: Wikipedia/façade_pattern

19. OpenStack Oslo common lib
 oslo.cache: a library for caching based on dogpile
 oslo.concurrency: a project with helpers managing external
processes and task synchronization. E.g: check host
resources.
 oslo.config: an extensive library for parsing configuration files
and command line arguments.
 oslo.log: a logging configuration library.
 oslo.service: helper library that provides functionality for
running OpenStack services.  nova-api service
 oslo.messaging: a library that provides a messaging API which
supports RPC and notifications over a number of different
messaging transports.
 oslo.serialization
Ref: https://wiki.openstack.org/wiki/Oslo
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20. pbr
 Python Build Reasonableness: using setuptools to deploy your
code and expose via entry points.
 setup.cfg
 policy.json: will be checked each time an API is called
 Can be modified for reasonable purpose
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21. WSGI – PEP 0333
nova/wsgi.py
 WSGI Application
 Python callable passed two arg (WebOb)
• Env
• Start_response function  callback function
 WSGI Server
 Call the application
 WSGI Middleware (Paste)
 Both a server and application
 Use to wrap request
Paste Deploy will automatically find and config WSGI
applications and servers
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Ref: WSGI – Aseries of Tubes by Ian Bickings (The
Open Planning Project)

22. 21 Copyright 2016 Fujitsu Vietnam Limited

23. Paste
 http://pythonpaste.org/
 Check api-paste.ini file below and see DEMO
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Middleware filter Apps
Filter flow

24. Stevedore (1)
 Extension manager library
 https://github.com/openstack/stevedore
 http://docs.openstack.org/developer/stevedore/
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25. Stevedore (2)
 Check nova/api/openstack/compute/disk_config.py
 Easier to write new API
 Easier to write new plugin
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26. Stevedore (3)
 Where is extension manager ?
nova/api/openstack/__init__.py – ApiRouterv21 class
nova/compute/monitors/__init.py__
and more …
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27. Routes
 Mapping URLs to controllers+actions. URLs are mapped to
‘action’ methods on ‘controller’ classes in
nova/api/openstack/__init__.py, class ApiRouter._init_ and
ApiRouterv21.__init__
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Stevedore ext mgr
Map URL from alias
/v2.1/​{tenant_id}​/os-aggregates
Ref: api-ref site OpenStack

28. Agenda
Copyright 2016 Fujitsu Vietnam Limited
1. Architecture overview
2. Data Flows
3. Nova Code Structure Components
4. Conclusion
27

29. Nova code structure
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documentation
For packaging, deploying and testing (using tox)
Source Codes
For setup with devstack
Configuration files
XenServer plugin for using with nova

30. Nova code structure
 Configuration files
29 Copyright 2016 Fujitsu Vietnam Limited
Rootwrap.d conf: allow a service-specific
unprivileged user to run a number of actions as
the root user, in the safest manner possible.
https://wiki.openstack.org/wiki/Rootwrap
Nova API config (paste + policy)
Nova Cells config sample
http://docs.openstack.org/mitaka/config-reference/compute/cells.html
Docs
Logging sample config file
Nova config generator file. Using oslo-config-generator
tool or tox –egenconfig for a sample of nova.conf file.
Nova.conf sample file will list all nova config options
and default value of each option.

31. Nova code structure
 Configuration files
30 Copyright 2016 Fujitsu Vietnam Limited
Rootwrap.d conf: allow a service-specific
unprivileged user to run a number of actions as
the root user, in the safest manner possible.
https://wiki.openstack.org/wiki/Rootwrap
Nova API config (paste + policy)
Nova Cells config sample
http://docs.openstack.org/mitaka/config-reference/compute/cells.html
Docs
Logging sample config file
Nova config generator file. Using oslo-config-generator
tool or tox –egenconfig for a sample of nova.conf file.
Nova.conf sample file will list all nova config options
and default value of each option. (~810 option)

32. Nova source code
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Executable system script, bundle and expose via pbr.
e.g.: nova-api, nova-compute..
Centralize configuration options for all nova subcomponents
(WIP  Newton version)
Nova compute virt (virtualization) driver  driver parity approach

33. Nova source code
32 Copyright 2016 Fujitsu Vietnam Limited
Executable system script, bundle and expose via pbr.
e.g.: nova-api, nova-compute..
Centralize configuration options for all nova subcomponents
(WIP  Newton version)
Nova compute virt (virtualization) driver  driver parity approach
HANDS-ON DEMO

34. Agenda
Copyright 2016 Fujitsu Vietnam Limited
1. Architecture overview
2. Nova Code Structure Components
3. Data Flows
4. Conclusion
33

35. Conclusion
34 Copyright 2016 Fujitsu Vietnam Limited
WSGIService
oslo_service lib
Paste filters
Paste/Paste.Deploy lib via api-paste.ini
WebOb lib for WSGI req/res wrapper
1. RESTful req 2. WSGI Req
APIRouter
RoutesMiddleware
3. Filtered req
Routes lib
Extension
Controller:
index/show/delete/
create..
Extension
Controller:
index/show/delete/
create..
Extension
Controller:
index/show/delete/
create..
4. Req dispatching
stevedore lib for managing ext, ctrl
Expose via pbr entrypoint
oslo_conf
Façade/Decorator pattern
oslo_message
RPC

36. THANK YOU!
Copyright 2016 Fujitsu Vietnam Limited35