Network Deployment (Distributed operating systems), v8.0 > Reference > Developer best practices
Scheduler configuration or topology
The scheduler uses a database to persist information concerning which tasks to run and when. Errors might occur when changing the application server topology or when changing the application or server configuration. When you change the configuration or topology, carefully consider how this action affects the scheduler.
Restricting security
If you created tasks with an application server while security is disabled, and you later decide to enable security, then the scheduler might have difficulty running tasks. When you create a task, the security context of the application thread is automatically stored with the task. If security is not stored with the task (see Scheduler task user authorization), and you later enable security on the server or application where the task is to run, then the following errors might be logged:
SECJ0053E: Authorization failed for /UNAUTHENTICATED while invoking (Home)com/ibm/websphere/scheduler /TaskHandler create:2 securityName: /UNAUTHENTICATED;accessID: UNAUTHENTICATED is not granted any of the required roles: MySecurityRoleBefore you enable security on the server or application, determine if any tasks might be adversely affected. If so, use the Scheduler API or WASScheduler MBean to cancel the tasks and recreate them after you configure security.
Application server topology changes
The scheduler stores javax.ejb.HomeHandle objects for TaskHandler, NotificationSink and UserCalendar homes when the task is created. When you run the task later, these home handles are reinflated and used to access the EJB component home. When the home handle references an EJB on a single-server environment, the home handles have affinity to that server. When the home handle references an EJB component on a cluster, then the home handles have affinity to the cluster.
If the application server or the Workload Managed (WLM) cluster that a home handle is referencing is not available, then the scheduler fails to run the task, and the following error is logged:
SCHD0063E: A task with ID 123 failed to run on Scheduler MyScheduler (sched/MyScheduler) because of an exception: {cause of failure}If you upgrade the application server to a cluster, or if the ORB (ORB) ORB_LISTENER_ADDRESS is not set to a fixed port number (see Configuring Inbound Transports), then the task might also fail, since the information stored within the home handle does not have the appropriate information to find the desired server.
Upgrade to a scheduler cluster
A scheduler cluster (not to be confused with a WLM cluster) is a collection of scheduler configurations on different application servers that share the same JNDI name, JDBC data source and table prefix. If you upgrade a stand-alone scheduler to a clustered scheduler, then the application and any associated resources that the application requires must be available. If this is not the case, the scheduled task fails to run and error messages might be logged:
SCHD0103W: The Scheduler MyScheduler (sched/MyScheduler) was unable to run task 123 because the application or module is unavailable: MyTaskHandlerEJBTo avoid issues with application availability and achieve optimal results, use the same servers in a scheduler cluster as those used in a WLM cluster.
Reuse scheduler tables
When changing any topology, moving from development to production environments, or making any configuration changes that make the environment more restrictive, you might get optimal results if you use a different set of scheduler tables. Reusing scheduler tables that have scheduled tasks from previous releases without careful planning might cause problems:
- EJB components running on unexpected application servers.
- Tasks failing to run due to invalid or missing security credentials.
- Tasks failing to run due to invalid or missing Java EE context information.
Diagnosing such problems is challenging and requires analyzing logs on all servers that have a scheduler installed and configured. When the problem tasks are located, the tasks can be cancelled using the Scheduler APIs, or the tables can be dropped and recreated.
Task management methods using a scheduler
Configure inbound transports
Create the database for schedulers
Manage schedulers
Related
Schedulers collection