DNS and Network Fail Over

Understanding Oracle Virtual Directory Fault Tolerance 7-3

7.4 Proxied Sources Fail Over

Oracle Virtual Directory’s LDAP Adapter provides sophisticated fail over and load balancing management for all LDAP-compliant data repositories. For any proxied source or adapter you can define multiple remote host replicas and specify the following characteristics: ■ ReadWrite or Read Only Master versus Replica node ■ Percentage load distribution or switch only on failure Figure 7–1 shows an example of how Oracle Virtual Directory’s LDAP Adapter performs transaction load-balancing: Figure 7–1 Oracle Virtual Directory LDAP Adapter and Transaction Load-Balancing Oracle Virtual Directory includes configurable connection handling settings that allow you to specify the following: ■ Heartbeat Interval : How often Oracle Virtual Directory verifies online status of a proxy. The heartbeat interval continually verifies availability of a server. If a proxy goes offline, Oracle Virtual Directory automatically removes it from its list of active servers and distributes load to other defined replicas. When the heartbeat interval verifies a server is available again, the server is put back on the available list. ■ Time-out Interval : How long in milliseconds Oracle Virtual Directory waits before determining a connection has failed. When a connection fails, Oracle Virtual Directory automatically tries the next server on its replica list. If no proxied servers are responding, the LDAP client receives the DSA unavailable error. ■ Criticality : How Oracle Virtual Directory determines when the proxy’s results are critical to an overall query. If a query requires responses from multiple adapters, Oracle Virtual Directory responds with an error if any sources are unavailable because all adapters could not be queried and have been designated critical. In some situations you may want to have Oracle Virtual Directory return results even if only some servers could be queried. To allow Oracle Virtual Directory to return Application User Oracle Oracle Virtual Directory with LDAP Adapter Directory Replicas Primary Directory Write Traffic 20 40 40 Load Balanced Read Traffic