2.5 Servers and Server Pools

An Oracle VM environment is built up out of an extensible set of Oracle VM Servers, which are controlled by a single Oracle VM Manager. The Oracle VM Manager runs the database that contains all information about both the physical and the virtual infrastructure. In addition, it hosts the web browser interface that is used to configure and manage the entire environment. Communication between the Oracle VM Manager and the Oracle VM Servers, in order to execute operations on and through the servers, is relayed via the Oracle VM Agent, which is present on all the servers in the environment.

Oracle VM Servers are discovered based on their IP address or host name through Oracle VM Manager. Additional servers can be installed and discovered at any time as the need for capacity grows. The Oracle VM Servers provide computing capacity to the virtual machines they host: CPU and RAM. They also host the storage plug-ins that are used to connect with shared, attached file-based and block-based storage offered by other hardware in the data center. For more details, see Section 2.6, “Storage” in this chapter, and Chapter 4, Managing Storage.

Oracle VM Servers are members of a server pool. Server pools use a virtual IP address and elect one master server that handles interactions with the Oracle VM Manager. If the master server goes down, another server in the pool immediately takes over the master function and the server pool remains reachable at the virtual IP address. Virtual machines running on a failing server can be restored on another server in the pool. This is possible because all members of the server pool have access to the same shared storage, where virtual machine configuration, disks, templates etc. are stored.

In a clustered server pool, which is the typical configuration, high availability is enabled for the virtual machines they host. In the case that a server in a clustered server pool becomes unavailable, the virtual machines that it was hosting are made available using one of the other servers within the pool. Clustered server pools use a shared ocfs2 pool file system for the cluster heartbeating function, configuration and other clustering information. Clustering and ocfs2 enable important advanced functionality such as shared block-based storage access, policies for fail over, load balancing and power management, etc. For details about server pools, clustering and ocfs2, see Chapter 6, Managing Server Pools and Oracle VM Servers.

An Oracle VM environment can consist of several server pools. This is a design decision: like in any data center it may be preferred to subdivide resources into groups, isolate these from each other, and assign them to different users (departments, teams, administrators, customers and so on).