How Servers Exchange Load Balancing Information
There is one load balancing service in each Netscape Application Server. Each load balancing service calculates the Server Load and AppLogic Performance values for the server that hosts the load balancing service. The load balancer then broadcasts, at the broadcast interval, its calculated values to the load balancing services of the other Netscape Application Servers in the enterprise.
You can set the broadcast time intervals for each load balancing service. For more information about setting those times, see "Adjusting Update and Broadcast Intervals."
Each load balancing service compares the values received with the values of its host and calculates which Netscape Application Server is currently best suited to process new requests. This decision is made for each distributed AppLogic object and a list of available servers for each object is maintained by the load balancing service.
The Netscape Application Server best suited to process requests for an object is ranked first in the list, followed by, in order, the other servers that are able to process requests for that object. The load balancer service updates this order each time it receives a broadcast from another Netscape Application Server or re-calculates its own server's values. The other server are backups to the first server and the first server can forward a request to one of the other servers at any time.
Netscape Application Servers can pass requests to better suited servers up to a maximum number of hops. When an AppLogic object reaches that maximum number, it must be processed by the server to which the object was last passed. For information about setting the maximum number of times an AppLogic object can be passed from one server to another, see "Adjusting Update and Broadcast Intervals."
Network Traffic Created by Load Balancing
Load balancing information is exchanged with only those Netscape Application Servers for which load balancing is enabled. Each server sends about 128 bytes of information when it broadcasts its calculated values. This value does not include network packet overhead. If a request is routed to another Netscape Application Server, the hop size is at least 16 bytes, but could be more depending on the number of ValList variables.
The exchange of the Server Load values occurs between all Netscape Application Servers in the enterprise configured for load balancing. In contrast, the AppLogic Performance values are exchanged with only the Netscape Application Servers that host the same AppLogic objects and distribute requests for those objects.
How Load Balancing Servers Communicate
Netscape Application Servers transfer load balancing information using a multicast server. For more information about multicast servers, see "About Multicast Communication."
For information about changing the multicast address for load balancing, see "Changing the Multicast Host Address for Load Balancing."
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