Dynamic Load Balancing

In an environment with multiple NAS installations, incoming requests first pass through the Load Balancing system. The Load Balancing system enables the NAS plug-in in the Web server to direct each request to the server best suited to process it.

Response-Time Load Balancing

The Web server plug-in considers response time data as requests enter and leave the plug-in, then uses this data to load balance future requests. Because there is no interprocess communication involved and per-request resource usage is not factored into the load-balancing decisions, this is a simpler method than server-based load balancing.

User-Defined Load Balancing

Alternatively, each application server can use a combination of hardware resource profiles (including CPU load and disk I/O) and Request Execution profiles (including result caching and servlet execution rate) to load balance individual requests. Server and request statistics are communicated from one NAS machine to another in a cluster via multicasting. Multicasting gives more control to the administrator and is suitable for sophisticated scenarios.

Load Monitor

The Load Monitor takes a snapshot of server load based on administrator-configured interval settings. The Load Monitor then tabulates resource availability and system performance.

Load Balancer

The Load Balancer uses the load and performance statistics retrieved by the Load Monitor to determine the server with the most available resources to handle an incoming request. Each instance of NAS has its own load-balancing module that makes routing decisions based on load-balancing properties.

Fine Grained

There are many load-balancing configuration parameters. Administrators can tune these parameters using NAS Administrator.

Sticky Load Balancing

This option is enabled per application component. When a session requests one of its sticky components, that first request is load balanced normally. But for the remaining life of that session, any further requests to sticky components will be directed to the same server. This option is useful for certain applications components that cannot distribute session and state information, or when an application component can use cached results that are stored on a single server.