4-6 Using Clusters for Oracle WebLogic Server
Cluster membership should not change during the deployment process. After initiating deployment, do not:
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add or remove Managed Servers to the target cluster
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shut down Managed Servers in the target cluster
4.4.3.1 WebLogic Server Supports Relaxed Deployment Rules
Previous versions of WebLogic Server imposed these restrictions on deployment to clusters:
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No partial deployment—If one or more of the Managed Servers in the cluster are unavailable, the deployment process is terminated, and an error message is
generated, indicating that unreachable Managed Servers should be either restarted or removed from the cluster before attempting deployment.
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Pinned services cannot be deployed to multiple Managed Servers in a cluster—If an application is not deployed to the cluster, you can deploy it to one and only one
Managed Server in the cluster.
4.4.3.1.1 Deployment to a Partial Cluster is Allowed By default, WebLogic Server allows
deployment to a partial cluster. If one or more of the Managed Servers in the cluster are unavailable, the following message may be displayed:
Unable to contact servername. Deployment is deferred until servername becomes available.
When the unreachable Managed Server becomes available, deployment to that server instance will be initiated. Until the deployment process is completed, the Managed
Server may experience failures related to missing or out-of-date classes.
4.4.3.1.2 Deploying to Complete Clusters in WebLogic Server You can ensure that
deployment is only performed if all Managed Servers in the cluster are reachable by setting ClusterConstraintsEnabled. When ClusterConstraintsEnabled is
set to true, a deployment to a cluster succeeds only if all members of the cluster are reachable and all can deploy the specified files. See Enforcing Consistent Deployment
to All Configured Cluster Members in Deploying Applications to Oracle WebLogic Server.
4.4.3.1.3 Pinned Services can be Deployed to Multiple Managed Servers. It is possible to
target a pinned service to multiple Managed Servers in a cluster. This practice is not recommended. The load-balancing capabilities and scalability of your cluster can be
negatively affected by deploying a pinned service to multiple Managed Servers in a cluster. If you target a pinned service to multiple Managed Servers, the following
message is printed to the server logs:
Note: If you deploy an application to a Managed Server that is
partitioned at the time of deployment—running but not reachable by the Administration Server—problems accessing the Managed Server
can occur when that Managed Server rejoins the cluster. During the synchronization period, while other clustered Managed Servers
re-establish communications with the previously partitioned server instance, user requests to the deployed applications and attempts to
create secondary sessions on that server instance will fail. The risk of this circumstance occurring can be reduced by setting
ClusterConstraintsEnabled, as described in Enforcing Consistent Deployment to All Configured Cluster Members in
Deploying Applications to Oracle WebLogic Server.
Understanding Cluster Configuration 4-7
Adding server servername of cluster clustername as a target for module modulename. This module also includes server servername that
belongs to this cluster as one of its other targets. Having multiple individual servers in a cluster as targets instead of having the entire
cluster as the target can result in non-optimal load balancing and scalability. Hence this is not usually recommended.
4.5 Methods of Configuring Clusters
There are several methods for configuring a clusters:
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Configuration Wizard The Configuration Wizard is the recommended tool for creating a new domain or
cluster. See Introduction in Creating Domains Using the Configuration Wizard. See Select Optional Configuration for information about creating and configuring a
cluster.
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WebLogic Server Administration Console The Administration Console is a graphical user interface GUI to the
Administration Service. It allows you to perform a variety of domain configuration and monitoring functions.
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WebLogic Server Application Programming Interface API You can write a program to modify the configuration attributes, based on the
configuration application programming interface API provided with WebLogic Server. This method is not recommended for initial cluster implementation.
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WebLogic Scripting Tool WLST The WebLogic Scripting Tool WLST is a command-line scripting interface that
system administrators and operators use to monitor and manage WebLogic Server instances and domains. For more information, see Oracle WebLogic Scripting Tool.
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Java Management Extensions JMX JMX is the Java EE solution for monitoring and managing resources on a network.
WebLogic Server provides a set of MBeans that you can use to configure, monitor, and manage WebLogic Server resources through JMX.
