The minimum supported cloud architecture is a high availability configuration that comprises three cloud servers running on three separate computers.
Two of the cloud servers, the cloud partners, are identical and oversee all activity between hosts and servers in the cloud. If one partner goes offline, the other partner takes over to keep the cloud running until the first partner is restored, or until another cloud partner is configured. The cloud partners must always be running and available to other cloud servers.
The third computer hosts the cloud arbiter, whose job it is to monitor availability of the cloud partners and ensure that the other cloud partner takes over in the event that one of the cloud partners goes offline.
All other servers in the cloud are referred to simply as cloud servers. Cloud servers are used to run the tenant databases. Although you can run cloud servers on the cloud partners, for improved performance, especially in clouds with a high volume of activity, consider running tenant databases on separate computers.