SHOP TALK : USING CLUSTERING FOR MAXIMUM AVAILABILITY Most applications today require multiple servers to handle the load for better performance and a fail-over feature to enable around-the-clock access to the application. This can be achieved by using clustering technology. A cluster is a group of servers started in a coordinated manner. Servers in a cluster keep track of one another's state. It is transparent to the client which server in the cluster processes a request. For an application to have the load balancing and fail-over features, you must target the application to a cluster instead of to a single server. To start servers in a cluster, first you need to create a cluster via the Administration Console. Click the cluster folder in the pane on the left, and then click the Configure a New Cluster link on the right. On the General tab, specify a logical name for the cluster and the cluster address (the <IP address>:<port> of all the servers you want to include in this cluster), with as the delimiter . On the Multicast tab, specify the multicast address and the multicast port. These two values are unique for a cluster. On the Servers tab, select the servers you want to move from the Available list to the Chosen list. This list should match the server list specified in the cluster address. After the cluster is created, restart the servers. You'll notice a line stating "Starting Cluster Service" in each server log file. After the servers are started in a cluster, you must deploy the application to the cluster through the Administration Console. Click the application name under Deployments in the pane on the left. On the right, click the Targets tab. The clusters that have been created are listed under the Clusters section. Select the cluster, and then click Apply to deploy the application to a cluster. You have the option to deploy to all servers in the cluster or to a selected set of servers. Depending on the type of application, you should specify certain elements in the application's deployment descriptor. |