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How the OpenStack instance process to launch in OVN integrated enviroment?

Updated 2020-02-03T04:30:21+00:00

Issue

  • In OVN integrated environment how the OpenStack instance has schedule and launch?

Environment

  • Red Hat OpenStack Director v.13
  • Red Hat OpenStack Director v.14

Resolution

  • The launch process uses a combination of REST API calls to OpenStack services, and message broker RPC calls for coordination between service components.

Instance Process Flow

Instance Launch Process

  1. Using the dashboard or the command-line client, the user's account credentials are sent as a REST API call to the identity service endpoint. After successful authentication, the identity service generates and returns an authentication token (auth token) to the user. The auth token is included with subsequent REST calls to other services, to permit those services to perform actions on behalf of this user.

  2. The instance launch request and the auth token are sent as a REST API call to the compute service endpoint. nova_api relays the request to the identity service, which validates the auth token and returns allowed roles and permissions in the updated token header.

  3. nova_api creates a persistent database entry for the new instance, including the launch parameters in the original request. Other processes can obtain data from this entry, and update the current state to this persistent entry.

  4. nova_api publishes a rpc.call to a named message queue, requesting nova_scheduler to locate an acceptable compute node to host the new instance.

  5. nova_scheduler subscribes to the new instance request, reads filtering and weighing parameters from the instance database entry, reads cluster compute node data from the database, and updates the instance record with the selected compute host ID. nova_scheduler submits a rpc.call to a message queue, requesting that nova_compute initiate an instance launch.

  6. nova_compute subscribes to the new instance request, then publishes a rpc.call for nova_conductor to prepare for an instance launch.

  7. nova_conductor subscribes to the new instance request, reads the database entry to obtain the compute host ID and instance flavor with requested RAM, vCPUs, and disk configuration, and then publishes the new instance state to the message queue.

  8. nova_compute subscribes to the new instance request to retrieve the instance information. Using the image ID from the instance request, nova_compute sends a REST API call to the image service to obtain the requested image's URL. The glance_api service forwards the request to the identity service, which again validates the auth token and returns allowed roles and permissions in the updated token header.

  9. Using the image ID, glance_api retrieves image metadata from the image service database and returns the image URL to nova_compute. nova_compute loads the image from the image store using the URL.

  10. nova_compute sends a REST API call to the networking service, requesting allocation and configuration of network resources for the new instance. neutron_server forwards the request to the identity service, which again validates the auth token and returns allowed roles and permissions in the updated token header.

  11. neutron_server, as a cloud management system plug-in, reads and writes logical network resource definitions to the ovn-nb database. neutron_server checks for the existing network and creates new resources for needed ports, connections, and network parameters.

  12. The ovn-northd daemon reads from ovn-nb and translates the logical network configuration into logical data-path flows in the ovn-sb database. The additional physical network and port bindings are populated by the ovn-controller on the selected compute host.

  13. The ovn-controller reads the configuration from ovn-sb and updates the compute host's status in the physical network and the binding tables. ovn-controller connects to ovs-vswitchd as an OpenFlow controller to dynamically configure control over network traffic through OpenFlow rules on OVS bridges. neutron_server returns the L2 configuration obtained from the compute host libvirt driver, and the requested DHCP address, to the message queue. nova_compute writes this instance network state to the instance database entry.

  14. nova_compute sends a REST API call to the block storage service, requesting volume data for the new instance disks. cinder_api forwards the request to the identity service, which again validates the auth token and returns allowed roles and permissions in the updated token header.

  15. cinder_api publishes a rpc.call to a named message queue, requesting that cinder_scheduler create a volume of the requested size, or to locate the volume metadata for a volume that already exists.

  16. cinder_scheduler subscribes to the new instance request, creates or locates the volume, and then returns the requested metadata to nova_scheduler.

  17. nova_compute generates data for the compute node driver and executes the request using libvirt to create a VM on the compute host. The VM appears in the dashboard and in commands that list servers. nova_compute passes the volume information to libvirt.

  18. cinder_volume subscribes to the new instance request and retrieves the cluster map. libvirt then mounts the volume on the new instance.