Net8 supports two important advanced features: failover and load balancing. These options are actually related, and they are usually used in Oracle Parallel Server (OPS) environments. Failover allows you to configure Net8 such that failure to connect to one instance results in a connection attempt to a backup instance. Failover is used in high-availability environments to ensure that clients are always able to connect to a database. Load balancing allows you to distribute client connections among the various nodes accessing an OPS database.
Where Net8 is concerned, failover refers to the ability to switch to another database instance when the connection to the primary instance fails. Consider the situation shown in Figure 8.1 where a client connects to an instance named PROD01 in a Parallel Server environment. Under some circumstances, if the PROD01 instance fails, Net8 can automatically connect the client to the backup instance named PROD02.
Figure 8-1. Failover to a backup instance in an OPS environment
Connection failures can be broadly categorized as follows:
Those that occur while attempting to connect for the first time
Those that occur after a connection has been established
The first category is the easiest one to deal with. If you attempt to connect to an instance and for some reason that attempt fails, you can simply try again, ...