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Chapter 5 Using Application Server Clusters
This chapter describes how to use Application Server clusters. It contains the
following sections:
Overview of Clusters
A cluster is a named collection of server instances that
share the same applications, resources, and configuration information. You can group
server instances on different machines into one logical cluster and administer them
as one unit. You can easily control the lifecycle of a multi-machine cluster with
the DAS.
Clusters enable horizontal scalability, load balancing, and failover protection.
By definition, all the instances in a cluster have the same resource and application
configuration. When a server instance or a machine in a cluster fails, the load balancer
detects the failure, redirects traffic from the failed instance to other instances
in the cluster, and recovers the user session state. Since the same applications and
resources are on all instances in the cluster, an instance can failover to any other
instance in the cluster.
Working with Clusters
 To Create a Cluster
-
In the tree component, select the Clusters node.
-
On the Clusters page, click New.
The Create Cluster page
appears.
-
In the Name field, type a name for the cluster.
The name
must:
-
Consist only of uppercase and lowercase letters, numbers, underscores,
hyphens, and periods (.)
-
Be unique across all node agent names, server instance names, cluster
names, and configuration names
-
Not be domain
-
In the Configuration field, choose a configuration from the drop-down
list.
-
To create a cluster that does not use a shared configuration, choose default-config.
Leave the radio button labeled “Make a
copy of the selected Configuration” selected. The copy of the default configuration
will have the name cluster_name-config.
-
To create a cluster that uses a shared configuration, choose the configuration
from the drop-down list.
Select the radio button labeled “Reference
the selected Configuration” to create a cluster that uses the specified existing
shared configuration.
-
Optionally, add server instances.
You can also add server
instances after the cluster is created.
Before you create server instances
for the cluster, first create one or more node agents or node agent placeholders.
See To Create a Node Agent Placeholder
To create server instances:
-
In the Server Instances To Be Created area, click Add.
-
Type a name for the instance in the Instance Name field
-
Choose a node agent from the Node Agent drop-down list.
-
Click OK.
-
Click OK on the Cluster Created Successfully page that appears.
Equivalent asadmin command
create-cluster
See Also
For more details on how to administer clusters, server instances, and node agents,
see Deploying Node Agents.
To Create Server Instances for a Cluster
Before You Begin
Before you can create server instances for a cluster, you must first create
a node agent or node agent placeholder. See To Create a Node Agent Placeholder
-
In the tree component, expand the Clusters node.
-
Select the node for the cluster.
-
Click the Instances tab to bring up the Clustered Server Instances page.
-
Click New to bring up the Create Clustered Server Instance page.
-
In the Name field, type a name for the server instance.
-
Choose a node agent from the Node Agents drop-down list.
-
Click OK.
Equivalent asadmin command
create-instance
See Also
To Configure a Cluster
-
In the tree component, expand the Clusters node.
-
Select the node for the cluster.
On the General Information
page, you can perform these tasks:
-
Click Start Instances to start the clustered server instances.
-
Click Stop Instances to stop the clustered server instances.
-
Click Migrate EJB Timers to migrate the EJB timers from a stopped
server instance to another server instance in the cluster.
Equivalent asadmin command
start-cluster, stop-cluster, migrate-timers
See Also
To Start, Stop, and Delete Clustered Instances
-
In the tree component, expand the Clusters node.
-
Expand the node for the cluster that contains the server instance.
-
Click the Instances tab to display the Clustered Server Instances page.
On this page you can:
-
Select the checkbox for an instance and click Delete, Start, or Stop
to perform the selected action on all the specified server instances.
-
Click the name of the instance to bring up the General Information
page.
To Configure Server Instances in a Cluster
-
In the tree component, expand the Clusters node.
-
Expand the node for the cluster that contains the server instance.
-
Select the server instance node.
-
On the General Information page, you can:
-
Click Start Instance to start the instance.
-
Click Stop Instance to stop a running instance.
-
Click JNDI Browsing to browse the JNDI tree for a running instance.
-
Click View Log Files to open the server log viewer.
-
Click Rotate Log File to rotate the log file for the instance. This
action schedules the log file for rotation. The actual rotation takes place the next
time an entry is written to the log file.
-
Click Recover Transactions to recover incomplete transactions.
-
Click the Properties tab to modify the port numbers for the instance.
-
Click the Monitor tab to change monitoring properties.
See Also
To Configure Applications for a Cluster
-
In the tree component, expand the Clusters node.
-
Select the node for the cluster.
-
Click the Applications tab to bring up the Applications page.
On this page, you can:
-
From the Deploy drop-down list, select a type of application to deploy.
On the Deployment page that appears, specify the application.
-
From the Filter drop-down list, select a type of application to display
in the list.
-
To edit an application, click the application name.
-
Select the checkbox next to an application and choose Enable or Disable
to enable or disable the application for the cluster.
See Also
To Configure Resources for a Cluster
-
In the tree component, expand the Clusters node.
-
Select the node for the cluster.
-
Click the Resources tab to bring up the Resources page.
On this page, you can:
-
Create a new resource for the cluster: from the New drop-down list,
select a type of resource to create. Make sure to specify the cluster as a target
when you create the resource.
-
Enable or Disable a resource globally: select the checkbox next to
a resource and click Enable or Disalbe. This action does not remove the resource.
-
Display only resources of a particular type: from the Filter drop-down
list, select a type of resource to display in the list.
-
Edit a resource: click the resource name.
See Also
To Delete a Cluster
-
In the tree component, select the Clusters node.
-
On the Clusters page, select the checkbox next to the name of the cluster.
-
Click Delete.
Equivalent asadmin command
delete-cluster
See Also
To Migrate EJB Timers
If a server instance stops running abnormally or unexpectedly, it can be necessary
to move the EJB timers installed on that server instance to a running server instance
in the cluster. To do so, perform these steps:
-
In the tree component, expand the Clusters node.
-
Select the node for the cluster.
-
On the General Information page, click Migrate EJB Timers.
-
On the Migrate EJB Timers page:
-
From the Source drop-down list, choose the stopped server instance from
which to migrate the timers.
-
(Optional) From the Destination drop-down list, choose the
running server instance to which to migrate the timers.
If you leave
this field empty, a running server instance will be randomly chosen.
-
Click OK.
-
Stop and restart the Destination server instance.
If the source
server instance is running or if the destination server instance is not running, Admin
Console displays an error message.
Equivalent asadmin command
migrate-timers
See Also
To Upgrade Components Without Loss of Service
You can use the load balancer and multiple clusters to upgrade components within
the Application Server without any loss of service. A component can, for example, be a
JVM, the Application Server, or a web application.
This approach is not possible if:
 Caution – Upgrade all server instances in a cluster together. Otherwise, there
is a risk of version mismatch caused by a session failing over from one instance to
another where the instances have different versions of components running.
-
Stop one of the clusters using the Stop Cluster button on the General
Information page for the cluster.
-
Upgrade the component in that cluster.
-
Start the cluster using the Start Cluster button on the General Information
page for the cluster.
-
Repeat the process with the other clusters, one by one.
Because
sessions in one cluster will never fail over to sessions in another cluster, there
is no risk of version mismatch caused by a session’s failing over from a server
instance that is running one version of the component to another server instance (in
a different cluster) that is running a different version of the component. A cluster
in this way acts as a safe boundary for session failover for the server instances
within it.
See Also
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