Nova-Compute service

As you may already know, Nova is the original core component of OpenStack. From an architectural level, it is considered one of the most complicated components of OpenStack. Nova provides the compute service in OpenStack and manages virtual machines in response to service requests made by OpenStack users.

What makes Nova complex is its interaction with a large number of other OpenStack services and internal components, which it must collaborate with to respond to user requests for running a VM.

Let's break down the Nova service itself and look at its architecture as a distributed application that needs orchestration between different components to carry out tasks.

nova-api

The nova-api component accepts and responds to the end user and computes API calls. The end users or other components communicate with the OpenStack nova-api interface to create instances via the OpenStack API or EC2 API.

The nova-api initiates most orchestrating activities such as the running of an instance or the enforcement of some particular policies.

nova-compute

The nova-compute component is primarily a worker daemon that creates and terminates VM instances via the hypervisor's APIs (XenAPI for XenServer, Libvirt KVM, and the VMware API for VMware).

nova-network

The nova-network component accepts networking tasks from the queue and then performs these tasks to manipulate the network (such as setting up bridging interfaces or changing IP table rules).

Neutron is a replacement for the nova-network service.

nova-scheduler

The nova-scheduler component takes a VM instance's request from the queue and determines where it should run (specifically which compute host it should run on). At an application architecture level, the term scheduling or scheduler invokes a systematic search for the best outfit for a given infrastructure to improve its performance.

nova-conductor

The nova-conductor service provides database access to compute nodes. The idea behind this service is to prevent direct database access from the compute nodes, thus enhancing database security in case one of the compute nodes gets compromised.

By zooming out of the general components of OpenStack, we find that Nova interacts with several services such as Keystone for authentication, Glance for images, and Horizon for the web interface. For example, the Glance interaction is central; the API process can upload any query to Glance, while nova-compute will download images to launch instances.

Nova also provides console services that allow end users to access the console of the virtual instance through a proxy such as nova-console, nova-novncproxy, and nova-consoleauth.