More Content To be Added ... The request flow for provisioning an Instance goes like this: Dashboard or CLI gets the user credentials authenticates with Keystone via REST api. Keystone authenticate the credentials and generate & send back auth-token which will be used for sending request to other Components through REST-call. 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. nova-api receive the request and sends the request for validation auth-token and access permission to keystone. Keystone validates the token and sends updated auth headers with roles and permissions. nova-api interacts with nova-database. Creates initial db entry for new instance. nova-api sends the rpc.call request to nova-scheduler excepting to get updated instance entry with host ID specified. nova-scheduler picks the request from the queue. nova-scheduler interacts with nova-database to find an appropriate host via filtering and weighing. Returns the updated instance entry with appropriate host ID after filtering and weighing. nova-scheduler sends the rpc.cast request to nova-compute for ‘launching instance’ on appropriate host . nova-compute picks the request from the queue. nova-compute send the rpc.call request to nova-conductor to fetch the instance information such as host ID and flavor( Ram , CPU ,Disk). nova-conductor picks the request from the queue. nova-conductor interacts with nova-database. Return the instance information. nova-compute picks the instance information from the queue. 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. glance-api validates the auth-token with keystone. nova-compute get the image metadata. 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. quantum-server validates the auth-token with keystone. nova-compute get the network info. nova-compute does the REST call by passing auth-token to Volume API to attach volumes to instance. cinder-api validates the auth-token with keystone. nova-compute gets the block storage info. nova-compute generates data for hypervisor driver and executes request on Hypervisor( via libvirt or api).