1. Dashboard or CLI gets the user credential and does the REST call to Keystone for authentication.
   

2. Keystone authenticate the credentials and generate & send back auth-token which will be used for sending request to other Components through REST-call.

3. Dashboard or CLI convert the new instance request specified in  ‘launch instance’ or ‘nova-boot’ form to REST API request and send it to nova-api.

4. nova-api receive the request and sends the request for validation auth-token and access permission to keystone.

5. Keystone validates the token and sends updated auth headers with roles and permissions.

6. nova-api interacts with nova-database.

7. Creates initial db entry for new instance.

8.  nova-api sends the rpc.call request to nova-scheduler excepting to get  updated instance entry with host ID specified.

9. nova-scheduler picks the request from the queue.

10. nova-scheduler interacts with nova-database to find an appropriate host via filtering and weighing.

11. Returns the updated instance entry with appropriate host ID after filtering and weighing.

12. nova-scheduler sends the rpc.cast request to nova-compute for ‘launching instance’ on appropriate host .

13. nova-compute picks the request from the queue.

14. nova-compute send the rpc.call request to nova-conductor to fetch the instance information such as host ID and flavor( Ram , CPU ,Disk).

15. nova-conductor picks the request from the queue.

16. nova-conductor interacts with nova-database.

17. Return the instance information.

18. nova-compute picks the instance information from the queue.

19. nova-compute does the REST call by passing auth-token to glance-api  to get the Image URI by Image ID from glance and upload image from image storage.

20. glance-api validates the auth-token with keystone. 

21. nova-compute get the image metadata.

22. nova-compute does the REST-call by passing auth-token to Network API to allocate and configure the network such that instance gets the IP address. 

23. quantum-server validates the auth-token with keystone.

24. nova-compute get the network info.

25. nova-compute does the REST call by passing auth-token to Volume API to attach volumes to instance.

26. cinder-api validates the auth-token with keystone.

27. nova-compute gets the block storage info.

28. nova-compute generates data for hypervisor driver and executes request on Hypervisor( via libvirt or api).

     本文转自 wzlinux 51CTO博客，原文链接：http://blog.51cto.com/wzlinux/1964195，如需转载请自行联系原作者