You can use dynamic cluster custom properties
You can use the HttpSessionRebalanceOff custom property to disable HTTP session rebalancing.
With WebSphere® Extended Deployment Version 6.0 or later, HTTP session rebalancing is automatically enabled. You can use HTTP session rebalancing to reassign existing session affinities to new servers that become available for processing the given Web application. See HTTP session rebalancing for more information.
Use the HttpSessionRebalanceOff custom property if you want to return your configuration to the old HTTP session behavior, where session affinities are established with a particular application server and are not reassigned to any new servers that become available.
Session rebalancing is disabled by default on any dynamic clusters that consist of servers that are not running WebSphere Application Server, such as PHP or Tomcat servers, because you might have another session clustering mechanism deployed for those servers.
You might consider disabling HTTP session rebalancing if your session sizes are large. If your sessions are large, the cost of moving the sessions to a new server might be more than the benefit of taking the workload off of the original server. You can use Performance Monitoring Infrastructure (PMI) data to make the decision to turn off session rebalancing. You might see in your PMI data that response time, memory utilization, and processor utilization increases on specific servers to transfer the session information. See the WebSphere Application Server Network Deployment Information Center for more information about analyzing PMI data and best practices for using HTTP sessions.
If you leave session rebalancing on, as sessions become more evenly distributed, and memory and processor utilization also become more evenly distributed across the servers in the cluster. If a cluster is more balanced, it is easier for WebSphere Virtual Enterprise to make autonomic decisions.
Perform the following steps to disable HTTP session rebalancing:
To turn session rebalancing back onfor dynamic clusters that consist of WebSphere Application Server application servers, delete the custom property.
Use this custom property to define the number of dynamic cluster instances on a node.
Use this custom property only if the nodes in your dynamic cluster are heterogeneous and vary in power. If the nodes in your dynamic cluster are homogenous, you can define the number of dynamic cluster instances one time in the administrative console.
See Configuring vertical stacking for more information.
You can use the proactiveIdleStop custom property to stop dynamic cluster instances during periods of inactivity.
This custom property adds function to the If other dynamic clusters need resources, stop all instances of this cluster during periods of inactivity setting in the administrative console. With the administrative console setting, instances stop only if other clusters in the cell need the resources that are being used by the inactive instances. You also specify an amount of time to wait before stopping instances for the cluster. By setting this custom property, inactive instances stop even if the resources are not required elsewhere in the environment. The cluster instance goes idle in the amount of time that you specified in the administrative console setting.
You can set this custom property on all dynamic clusters by creating the custom property on the cell level. You can also create the custom property on a single dynamic cluster. If the property is set on both the cell and the dynamic cluster, the dynamic cluster setting is used.
For z/OS platforms, the serverSpecificShortNames custom property is specified on the dynamic cluster to indicate the specific short names of cluster members in a comma-separated list format, for example: SSN1,SSN2. Use commas to separate multiple short names. If you do not provide enough short names to be used for all of the cluster members, then the remaining cluster members are assigned generated generic short names, such as BBOS001, BBOS002, and so on.