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Configuring the Task Scheduling Component - Administration Guide 4.4.x - WSO2 Documentation
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The Task Scheduling component in a WSO2 product allows you to define specific tasks and to invoke them periodiclly. This functionality is used by WSO2 products such as WSO2 Enterprise Integrator (WSO2 EI), WSO2 Enterprise Service Bus (WSO2 ESB), and WSO2 Data Services Server (WSO2 DSS).

Follow the instructions given on this page to configure and set up this componentThen, see the respective product's documentation for details on how to use task scheduling.

The task scheduling component is configured in the tasks-config.xml file (stored in the <PRODUCT_HOME>/conf/etc/ directory for WSO2 EI, and in the <PRODUCT_HOME>/repository/conf/etc/ directory for other products).

Given below are the settings that you can configure in the tasks-config.xml file.

Step 1: Setting the task server mode

Select one of the following values for the <taskServerMode> element in the tasks-config.xml file:

  • AUTO: This is the default task handling mode. This setting detects if clustering is enabled in the server and automatically switches to CLUSTERED mode.
  • STANDALONE: This setting is used when a single instance of the product server is installed. That is, tasks will be managed locally within the server.
  • CLUSTERED: This setting is used when a cluster of product servers are put together. This requires Axis2 clustering to work. With this setting, if one of the servers in the cluster fail, the tasks will be rescheduled in one of the remaining server nodes. 

    Find out more about clustering WSO2 products.

Step 2: Configuring a cluster of task servers

If you have enabled the CLUSTERED task server mode in step 1, the following configuration elements in the tasks-config.xml file will be effective:

Setting the task server count

Use the parameter shown below to specify the number of servers (in the cluster) that can handle tasks. The task server count is set to "1" by default, which indicates that at least one node in the cluster is required for task handling.

<taskServerCount>1</taskServerCount>

Note that a product cluster begins the process of scheduling tasks only after the given number of servers are activated. For example, consider a situation where ten tasks are saved and scheduled in your product and there are five task-handling servers. As the individual servers become active, we do not want the first active server to schedule all the tasks. Instead, all five servers should become active and share the ten tasks between them.

Setting the default location resolver

The default location resolver controls how the scheduled tasks are shared by multiple sever nodes of a cluster. Note that the task server count should be a value larger than '1' for this location resolver setting to be effective. For example, if there are 5 task-handling servers in the cluster, the location resolver determines how the tasks get shared among the 5 servers.

Handling task failover

The location resolver parameter also controls how task failover is handled in a clustered environment. A scheduled task will only run in one of the nodes (at a given time) in a clustered environment. The task will failover to another node only if the first node fails. This parameter determines how nodes are selected for task failover.

One of the following options can be used for the location resolver.

  • RoundRobinTaskLocationResolver: Cluster nodes are selected on a round-robin basis and the tasks are allocated. This location resolver is enabled in the tasks-config.xml file by default as shown below.

    <defaultLocationResolver>
            <locationResolverClass>org.wso2.carbon.ntask.core.impl.RoundRobinTaskLocationResolver</locationResolverClass>
    </defaultLocationResolver>
  • RandomTaskLocationResolver: Cluster nodes are randomly selected and the tasks are allocated. If you want to enable this location resolver, you need to change the default configuration (shown above) in the tasks-config.xml file as shown below.

    <defaultLocationResolver>
            <locationResolverClass>org.wso2.carbon.ntask.core.impl.RandomTaskLocationResolver</locationResolverClass>
    </defaultLocationResolver>
  • RuleBasedLocationResolver: This allows you to set the criteria for selecting the cluster nodes to which the tasks should be allocated. The [task-type-pattern],[task-name-pattern], and [address-pattern of the server node] can be used as criteria. For example, with this setting, a scheduled task that matches a particular [task-type-pattern], and [task-name-pattern] will be allocated to the server node with a particular [address-pattern]. If multiple server nodes in the cluster match the [address-pattern], the nodes are selected on a round robin basis. This criteria is specified in the configuration using the <property> element. Therefore, you can define multiple properties containing different criteria. 
    Before you enable this location resolver, you need to first comment out the default location resolver that is already enabled in the task-config.xml file. You can then uncomment the following code block, and update the property values as required.

    <defaultLocationResolver>
            <locationResolverClass>org.wso2.carbon.ntask.core.impl.RuleBasedLocationResolver</locationResolverClass>
            <properties>
                <property name="rule-1">HIVE_TASK,HTTP_SCRIPT.*,192.168.1.*</property>
                <property name="rule-2">HIVE_TASK,.*,192.168.2.*</property>
                <property name="rule-5">.*,.*,.*</property>
            </properties>
    </defaultLocationResolver>

    As shown above, the property names (rule-1, rule-2 and rule-5) define a sequence for the list of properties in the configuration. Therefore, scheduled tasks will evaluate the criteria specified in each property according to the sequence. That is, rule-1 is checked before rule-2. In other words, the scheduled task will first check if it matches the criteria in rule-1, and if it does not, it will check rule-2.

    The RuleBasedLocationResolver allows you to address scenarios where tasks are required to be executed in specific server nodes first. Then, it can fail-over to another set of server nodes if the first (preferred) one is not available.

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