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Sun Cluster Data Services Developer's Guide for Solaris OS

Implementing a Scalable Resource

A scalable resource can be online on more than one node simultaneously. You can configure a scalable resource (which uses network load-balancing) to run on a global-cluster non-voting node as well. However, you can run such a scalable resource in only one node per Solaris host. Scalable resources include data services such as Sun Cluster HA for Sun Java System Web Server (formerly Sun Cluster HA for Sun ONE Web Server) and Sun Cluster HA for Apache.

The RGM provides a number of properties that support the implementation of a scalable resource.

Set the Boolean Failover resource type property to FALSE, to allow the resource to be configured in a resource group that can be online on more than one node at a time.

The Scalable resource property determines if the resource uses the cluster shared address facility. Set this property to TRUE because a scalable service uses a shared address resource to make the multiple instances of the scalable service appear as a single service to the client.

The RG_mode property enables the cluster administrator to identify a resource group as failover or scalable. If RG_mode is SCALABLE, the RGM allows Maximum_primaries to be assigned a value greater than 1. The resource group can be mastered by multiple nodes simultaneously. The RGM allows a resource whose Failover property is FALSE to be instantiated in a resource group whose RG_mode is SCALABLE.

The cluster administrator creates a scalable resource group to contain scalable service resources and a separate failover resource group to contain the shared address resources upon which the scalable resource depends.

The cluster administrator uses the RG_dependencies resource group property to specify the order in which resource groups are brought online and offline on a node. This ordering is important for a scalable service because the scalable resources and the shared address resources upon which they depend are located in different resource groups. A scalable data service requires that its network address (shared address) resources be configured to go up before the scalable data service is started. Therefore, the cluster administrator must set the RG_dependencies property (of the resource group that contains the scalable service) to include the resource group that contains the shared address resources.

When you declare the Scalable property in the RTR file for a resource, the RGM automatically creates the following set of scalable properties for the resource.

Network_resources_used

Identifies the shared-address resources on which this resource has a dependency. This list contains all network-address resources that appear in the properties Resource_dependencies, Resource_dependencies_weak, Resource_dependencies_restart, or Resource_dependencies_offline_restart.

The RGM automatically creates this property if the Scalable property is declared in the RTR file. If the Scalable property is not declared in the RTR file, Network_resources_used is unavailable unless it is explicitly declared in the RTR file.

If you do not assign a value to the Network_resources_used property, its value is updated automatically by the RGM, based on the setting of the resource-dependencies properties. You do not need to set this property directly. Instead, set the Resource_dependencies, Resource_dependencies_offline_restart, Resource_dependencies_restart, or Resource_dependencies_weak property.

Load_balancing_policy

Specifies the load-balancing policy for the resource. You can explicitly set the policy in the RTR file (or allow the default LB_WEIGHTED). In either case, the cluster administrator can change the value when he or she creates the resource (unless you set Tunable for Load_balancing_policy to NONE or FALSE in the RTR file). These are the legal values that you can use:

LB_WEIGHTED

The load is distributed among various nodes according to the weights that are set in the Load_balancing_weights property.

LB_STICKY

A given client (identified by the client IP address) of the scalable service is always sent to the same node of the cluster.

LB_STICKY_WILD

A given client (identified by the client's IP address) that connects to an IP address of a wildcard sticky service is always sent to the same cluster node regardless of the port number to which it is coming.

For a scalable service with a Load_balancing_policy of LB_STICKY or LB_STICKY_WILD, changing Load_balancing_weights while the service is online can cause existing client affinities to be reset. In this case, a different node might service a subsequent client request, even if the client had been previously serviced by another node in the cluster.

Similarly, starting a new instance of the service on a cluster might reset existing client affinities.

Load_balancing_weights

Specifies the load to be sent to each node. The format is weight@node,weight@node. weight is an integer that reflects the relative portion of load that is distributed to the specified node. The fraction of load that is distributed to a node is the weight for this node divided by the sum of all weights of active instances. For example, 1@1,3@2 specifies that node 1 receives ¼ of the load and node 2 receives ¾ of the load.

Port_list

Identifies the ports on which the application is listening. This property defaults to the empty string. You can provide a list of ports in the RTR file. Otherwise, the cluster administrator must provide the actual list of ports when creating the resource.

You can create a data service that the cluster administrator can configure to be either scalable or failover. To do so, declare both the Failover resource type property and the Scalable resource property as FALSE in the data service's RTR file. Specify the Scalable property to be tunable at creation.

The Failover property value FALSE allows the resource to be configured in a scalable resource group. The cluster administrator can enable shared addresses by changing the value of Scalable to TRUE when he or she creates the resource, to create a scalable service.

On the other hand, even though Failover is set to FALSE, the cluster administrator can configure the resource in a failover resource group to implement a failover service. The cluster administrator does not change the value of Scalable, which is FALSE. To support this scenario, you should provide a check in the Validate method on the Scalable property. If Scalable is FALSE, verify that the resource is configured into a failover resource group.

The Sun Cluster Concepts Guide for Solaris OS contains additional information about scalable resources.

Validation Checks for Scalable Services

Whenever you create or update a resource with the scalable property set to TRUE, the RGM validates various resource properties. If you do not configure the properties correctly, the RGM rejects the attempted update or creation.

The RGM performs the following checks: