The figure shows two nodes in a hardware cluster. Node 1 is active, and node 2 is passive. Both nodes share a shared storage that contains the Oracle home for Oracle HTTP Server and OC4J. Node 1 (the active node) runs Oracle HTTP Server and OC4J. Node 2 runs them only on failover. Node 2 also accesses the shared storage only on failover.
Node 1 is associated with a virtual hostname and IP address. This virtual hostname an IP address are associated with node 2 on failover.
Both nodes also run vendor clusterware. On Windows, you need Microsoft Cluster Server and Oracle Fail Safe.
As a variation, you can run Oracle Identity Management from Release 2 (10.1.2) with this topology.