Load Balancing Oracle Fusion Middleware Online Documentation Library

High Availability for WebLogic Server 3-15 There are a variety of ways to invoke the services of the Administration Server to accomplish configuration tasks. Whichever method is used, the Administration Server for a cluster must be running when you modify the configuration.

3.11.1 Administration Server Failure

The failure of an Administration Server for a domain does not affect the operation of managed servers in the domain. If an Administration Server for a domain becomes unavailable while the server instances it manages—clustered or otherwise—are up and running, those managed servers continue to run. If the domain contains clustered server instances, the load balancing and failover capabilities supported by the domain configuration remain available, even if the Administration Server fails. For instructions on re-starting an Administration Server, see the Oracle Fusion Middleware Using Clusters for Oracle Server.

3.11.2 Node Manager Failure

If Node Manager fails or is explicitly shut down, upon restart, it determines the server instances that were under its control when it exited. Node Manager can restart any failed server instances as needed.

3.12 Load Balancing

Load balancing configuration consists of three pieces of information: the load-balancing algorithm to be used, an indicator of whether local affinity should be applied, and weights that are assigned to each member of the topology to influence any routing algorithms that use weights. The load-balancing algorithm specifies how requests are load balanced across components. Oracle Fusion Middleware uses the following three load-balancing methods: ■ Round Robin - Requests are balanced across a list of available servers by selecting from the list sequentially. ■ Random - Requests are balanced across a list of available servers by selecting a random server on each request. Note: It is recommended particularly for systems with multiple Middleware homes or Oracle homes that the Administration Server listen address be explicitly set to the hostname on which it needs to be accessed by its clients. Note: If an Administration Server fails because of a hardware or software failure on its host machine, other server instances on the same machine may be similarly affected. However, the failure of an Administration Server itself does not interrupt the operation of managed servers in the domain. Note: It is advisable to run Node Manager as an operating system service, so that it restarts automatically if its host machine is restarted. 3-16 Oracle Fusion Middleware High Availability Guide ■ Weighted - Requests are balanced across a list of available servers using weights assigned to each server to determine the percentage of requests sent to each Local affinity determines whether clients show a preference to servers that run on the same machine to avoid network latency. If the flag is set to true, then requests are routed across the list of servers on the local machine using the load-balancing algorithm if any local servers are available. If no local servers are available, requests are routed to all available remote servers according to the load-balancing algorithm. If local affinity is set to false, requests are routed across all available servers local and remote based on the load-balancing algorithm. You configure weights as single integer values that are associated with component instances. You can assign weights to components that are not currently in a group, however, the weight is not used unless you later configure the component as a member of a group and select the weighted load-balancing algorithm. The weight is a unitless number. The percentage of requests to be sent to each member is calculated by summing the weights of all available members and dividing the weight for each member by the sum of the weights.

3.13 Multi Data Sources