The Overcloud is the resulting Red Hat OpenStack Platform environment created using the Undercloud. This includes one or more of the following node types:
Controller - Nodes that provide administration, networking, and high availability for the OpenStack environment. An ideal OpenStack environment recommends three of these nodes together in a high availability cluster.
A default Controller node contains the following components: horizon, keystone, nova API, neutron server, Open vSwitch, glance, cinder volume, cinder API, swift storage, swift proxy, heat engine, heat API, ceilometer, MariaDB, RabbitMQ. The Controller also uses Pacemaker and Galera for high availability services.
Compute - These nodes provide computing resources for the OpenStack environment. You can add more Compute nodes to scale out your environment over time.
A default Compute node contains the following components: nova Compute, nova KVM, ceilometer agent, Open vSwitch
Storage - Nodes that provide storage for the OpenStack environment. This includes nodes for:
Ceph Storage nodes - Used to form storage clusters. Each node contains a Ceph Object Storage Daemon (OSD). In addition, the director installs Ceph Monitor onto the Controller nodes in situations where it deploys Ceph Storage nodes.
Block storage (cinder) - Used as external block storage for HA Controller nodes. This node contains the following components: cinder volume, ceilometer agent, Open vSwitch.
Object storage (swift) - These nodes provide a external storage layer for Openstack Swift. The Controller nodes access these nodes through the Swift proxy. This node contains the following components: swift storage, ceilometer agent, Open vSwitch.