By understanding how the different installed nodes interact with each other you can administer the OpenStack Compute installation. OpenStack Compute offers many ways to install using multiple servers but the general idea is that you can have multiple compute nodes that control the virtual servers and a cloud controller node that contains the remaining Nova services.
The OpenStack Compute cloud works via the interaction of a series of daemon processes named nova-* that reside persistently on the host machine or machines. These binaries can all run on the same machine or be spread out on multiple boxes in a large deployment. The responsibilities of Services, Managers, and Drivers, can be a bit confusing at first. Here is an outline the division of responsibilities to make understanding the system a little bit easier.
Currently, Services are nova-api, nova-objectstore (which can be replaced with Glance, the OpenStack Image Service), nova-compute, and nova-network. Managers and Drivers are specified by configuration options and loaded using utils.load_object(). Managers are responsible for a certain aspect of the system. It is a logical grouping of code relating to a portion of the system. In general other components should be using the manager to make changes to the components that it is responsible for.
nova-api - The nova-api service receives xml requests and sends them to the rest of the system. It is a wsgi app that routes and authenticate requests. It supports the EC2 and OpenStack APIs. There is a nova-api.conf file created when you install Compute.
nova-objectstore - The nova-objectstore service is an ultra simple file-based storage system for images that replicates most of the S3 API. It can be replaced with OpenStack Image Service and a simple image manager or use OpenStack Object Storage as the virtual machine image storage facility. It must reside on the same node as nova-compute.
nova-compute - The nova-compute service is responsible for managing virtual machines. It loads a Service object which exposes the public methods on ComputeManager via Remote Procedure Call (RPC).
nova-network - The nova-network service is responsible for managing floating and fixed IPs, DHCP, bridging and VLANs. It loads a Service object which exposes the public methods on one of the subclasses of NetworkManager. Different networking strategies are available to the service by changing the network_manager configuration option to FlatManager, FlatDHCPManager, or VlanManager (default is VLAN if no other is specified).
