Most OpenStack clouds are made up of physical infrastructure nodes that fit into one of the following four categories:
Controller nodes: These usually run the application programming interface (API) services for all of the OpenStack components, including Glance, Nova, Keystone, and Neutron. In addition, controller nodes run the database and messaging servers and are often the point of management of the cloud via the Horizon dashboard. Most OpenStack API services can be installed on multiple controller nodes and can be load balanced to scale the OpenStack control plane.
Network nodes: These usually run DHCP and metadata services and can host virtual routers when the Neutron L3 agent is installed. In smaller environments, it is not uncommon to see controller and network node services collapsed onto the same server or set of servers. As the cloud grows in size, most network services can be broken out among other servers or installed on their own server for optimal performance.
Compute nodes: These usually run a hypervisor, such as KVM, Hyper-V, or Xen, or container software, such as LXC or Docker. In some cases, a compute node may also host virtual routers, especially when Distributed Virtual Routing (DVR) is configured. In proof-of-concept or test environments, it is not uncommon to see controller, network, and compute node services collapsed onto the same machine. This is especially common when using DevStack, a software package designed for developing and testing OpenStack code. All-in-one installations are not recommended for production use.
Storage nodes: These are usually limited to running software related to storage, such as Cinder, Ceph, or Swift. Storage nodes do not usually host any type of Neutron Networking service or agent and will not be discussed in this book.
When Neutron services are broken out among many hosts, the layout of services will often resemble the following diagram, though it can vary from environment to environment:
In this book, we will build a test environment on a single node that demonstrates basic OpenStack network functionality. This distribution of services will look like this:
