Sun Java System Application Server Enterprise Edition 8.1 2005Q2 High Availability Administration Guide

- Previous: Chapter 4 Configuring Load Balancing and Failover
- Next: Chapter 6 Managing Named Configurations

# Chapter 5 Using Application Server Clusters

This chapter describes how to use Application Server clusters. It contains the following sections:

- Overview of Clusters

- Working with Clusters

# 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

- To Create Server Instances for a Cluster

- To Configure a Cluster

- To Delete a Cluster

- To Configure Server Instances in a Cluster

- To Configure Applications for a Cluster

- To Configure Resources for a Cluster

- To Migrate EJB Timers

- To Upgrade Components Without Loss of Service

## To Create a Cluster

1. In the tree component, select the Clusters node.

2. On the Clusters page, click New.

   The Create Cluster page appears.

3. 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`

4. 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.

5. 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:

   1. In the Server Instances To Be Created area, click Add.

   2. Type a name for the instance in the Instance Name field

   3. Choose a node agent from the Node Agent drop-down list.

6. Click OK.

7. Click OK on the Cluster Created Successfully page that appears.

##### Equivalent asadmin command

`create-cluster`

##### See Also

- To Configure a Cluster

- To Create Server Instances for a Cluster

- To Configure Applications for a Cluster

- To Configure Resources for a Cluster

- To Delete a Cluster

- To Upgrade Components Without Loss of Service

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

1. In the tree component, expand the Clusters node.

2. Select the node for the cluster.

3. Click the Instances tab to bring up the Clustered Server Instances page.

4. Click New to bring up the Create Clustered Server Instance page.

5. In the Name field, type a name for the server instance.

6. Choose a node agent from the Node Agents drop-down list.

7. Click OK.

##### Equivalent asadmin command

`create-instance`

##### See Also

- What Is a Node Agent?

- To Create a Cluster

- To Configure a Cluster

- To Configure Applications for a Cluster

- To Configure Resources for a Cluster

- To Delete a Cluster

- To Upgrade Components Without Loss of Service

- To Configure Server Instances in a Cluster

## To Configure a Cluster

1. In the tree component, expand the Clusters node.

2. 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 Create a Cluster

- To Create Server Instances for a Cluster

- To Configure Applications for a Cluster

- To Configure Resources for a Cluster

- To Delete a Cluster

- To Upgrade Components Without Loss of Service

- To Migrate EJB Timers

## To Start, Stop, and Delete Clustered Instances

1. In the tree component, expand the Clusters node.

2. Expand the node for the cluster that contains the server instance.

3. 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

1. In the tree component, expand the Clusters node.

2. Expand the node for the cluster that contains the server instance.

3. Select the server instance node.

4. 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 Create a Cluster

- To Configure a Cluster

- To Create Server Instances for a Cluster

- To Configure Applications for a Cluster

- To Configure Resources for a Cluster

- To Delete a Cluster

- To Upgrade Components Without Loss of Service

- Recovering Transactions in Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Administration Guide

## To Configure Applications for a Cluster

1. In the tree component, expand the Clusters node.

2. Select the node for the cluster.

3. 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 Create a Cluster

- To Configure a Cluster

- To Create Server Instances for a Cluster

- To Configure Resources for a Cluster

- To Delete a Cluster

- To Upgrade Components Without Loss of Service

## To Configure Resources for a Cluster

1. In the tree component, expand the Clusters node.

2. Select the node for the cluster.

3. 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 Create a Cluster

- To Configure a Cluster

- To Create Server Instances for a Cluster

- To Configure Applications for a Cluster

- To Delete a Cluster

## To Delete a Cluster

1. In the tree component, select the Clusters node.

2. On the Clusters page, select the checkbox next to the name of the cluster.

3. Click Delete.

##### Equivalent asadmin command

`delete-cluster`

##### See Also

- To Create a Cluster

- To Configure a Cluster

- To Create Server Instances for a Cluster

- To Configure Applications for a Cluster

- To Configure Resources for a Cluster

- To Upgrade Components Without Loss of Service

## 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:

1. In the tree component, expand the Clusters node.

2. Select the node for the cluster.

3. On the General Information page, click Migrate EJB Timers.

4. On the Migrate EJB Timers page:

   1. From the Source drop-down list, choose the stopped server instance from which to migrate the timers.

   2. (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.

   3. Click OK.

5. 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 Configure a Cluster

- Configuring the EJB Timer Service Settings in Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Administration Guide

## 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:

- You change the schema of the high-availability database (HADB). For more information, see Chapter 3, Administering High Availability Database

- You perform an application upgrade that involves a change to the application database schema.

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.

1. Stop one of the clusters using the Stop Cluster button on the General Information page for the cluster.

2. Upgrade the component in that cluster.

3. Start the cluster using the Start Cluster button on the General Information page for the cluster.

4. 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

- To Create a Cluster

- To Configure a Cluster

- To Create Server Instances for a Cluster

- To Configure Applications for a Cluster

- To Configure Resources for a Cluster

- To Delete a Cluster

- Previous: Chapter 4 Configuring Load Balancing and Failover
- Next: Chapter 6 Managing Named Configurations

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