The request flow for provisioning an instance goes like this: The dashboard or CLI gets the user credentials and authenticates with the Identity Service via REST API. The Identity Service authenticates the user with the user credentials, and then generates and sends back an auth-token which will be used for sending the request to other components through REST-call. The dashboard or CLI converts the new instance request specified in launch instance or nova-boot form to a REST API request and sends it to nova-api. nova-api receives the request and sends a request to the Identity Service for validation of the auth-token and access permission. The Identity Service validates the token and sends updated authentication headers with roles and permissions. nova-api checks for conflicts with nova-database. nova-api creates initial database entry for a new instance. nova-api sends the rpc.call request to nova-scheduler expecting to get updated instance entry with host ID specified. nova-scheduler picks up the request from the queue. nova-scheduler interacts with nova-database to find an appropriate host via filtering and weighing. nova-scheduler returns the updated instance entry with the appropriate host ID after filtering and weighing. nova-scheduler sends the rpc.cast request to nova-compute for launching an instance on the appropriate host. nova-compute picks up the request from the queue. nova-compute sends the rpc.call request to nova-conductor to fetch the instance information such as host ID and flavor (RAM, CPU, Disk). nova-conductor picks up the request from the queue. nova-conductor interacts with nova-database. nova-conductor returns the instance information. nova-compute picks up the instance information from the queue. nova-compute performs the REST call by passing the auth-token to glance-api. Then, nova-compute uses the Image ID to retrieve the Image URI from the Image Service, and loads the image from the image storage. glance-api validates the auth-token with keystone. nova-compute gets the image metadata. nova-compute performs the REST-call by passing the auth-token to Network API to allocate and configure the network so that the instance gets the IP address. neutron-server validates the auth-token with keystone. nova-compute retrieves the network info. nova-compute performs the REST call by passing the auth-token to Volume API to attach volumes to the instance. cinder-api validates the auth-token with keystone. nova-compute retrieves the block storage info. nova-compute generates data for the hypervisor driver and executes the request on the hypervisor (via libvirt or API).