Scheduler

Schedule background tasks in NSO.

NSO includes a native time-based job scheduler suitable for scheduling background work. Tasks can be scheduled to run at particular times or periodically at fixed times, dates, or intervals. It can typically be used to automate system maintenance or administrative tasks.

Scheduling Periodic Work

A standard Vixie Cron expression is used to represent the periodicity in which the task should run. When the task is triggered, the configured action is invoked on the configured action node instance. The action is run as the user that configured the task.

Example: To schedule a task to run sync-from at 2 AM on the 1st of every month, we do:

admin(config)# scheduler task sync schedule "0 2 1 * *" \
action-name sync-from action-node /devices

If the task was added through an XML init file, the task will run with the system user, which implies that AAA rules will not be applied at all. Thus, the task action will not be able to initiate device communication.

If the action node instance is given as an XPath 1.0 expression, the expression is evaluated with the root as the context node, and the expression must return a node-set. The action is then invoked on each node in this node-set.

Optionally, action parameters can be configured in XML format to be passed to the action during invocation.

admin(config-task-sync)# action-params "<device>ce0</device><device>ce1</device>"
admin(config)# commit

Once the task has been configured, you can view the next run times of the task:

admin(config)# scheduler task sync get-next-run-times display 3
next-run-time [ 2017-11-01 02:00:00+00:00 2017-12-01 02:00:00+00:00 2018-01-01 02:00:00+00:00 ]

You could also see if the task is running or not:

admin# show scheduler task sync is-running
is-running false

Schedule Expression

A standard Vixie Cron expression is a string comprising five fields separated by white space that represents a set of times. The following rules can be used to create an expression.

The table below shows expression rules.

Field	Allowed values	Allowed special characters
Minutes	0-59	* , - /
Hours	0-23	* , - /
Day of month	1-31	* , - /
Month	1-12 or JAN-DEC	* , - /
Day of week	0-6 or SUN-SAT	* , - /

The following list describes the legal special characters and how you can use them in a Cron expression.

• Star (*). Selects all values within a field. For example, * in the minute field selects every minute.

• Comma (,). Commas are used to specify additional values. For example, using MON,WED,FRI in the day of week field.

• Hyphen (-). Hyphens define ranges. For example 1-5 in the day of week field indicates every day between Monday and Friday, inclusive.

• Forward slash (/). Slashes can be combined with ranges to specify increments. For example, */5 in the minutes field indicates every 5 minutes.

Scheduling Periodic Compaction

Compaction in NSO can take a considerable amount of time, during which transactions could be blocked. To avoid disruption, it might be advantageous to schedule compaction during times of low NSO utilization. This can be done using the NSO scheduler and a service. See examples.ncs/development-guide/periodic-compaction for an example that demonstrates how to create a periodic compaction service that can be scheduled using the NSO scheduler.

Scheduling Non-recurring Work

The scheduler can also be used to configure non-recurring tasks that will run at a particular time.

admin(config)# scheduler task my-compliance-report time 2017-11-01T02:00:00+01:00 \
action-name check-compliance action-node /reports

A non-recurring task will by default be removed when it has finished executing. It will be up to the action to raise an alarm if an error occurs. The task can also be kept in the task list by setting the keep leaf.

Scheduling in a HA Cluster

In a HA cluster, a scheduled task will by default be run on the primary HA node. By configuring the ha-mode leaf a task can be scheduled to run on nodes with a particular HA mode, for example scheduling a read-only action on the secondary nodes. More specifically, a task can be configured with the ha-node-id to only run on a certain node. These settings will not have any effect on a standalone node.

admin(config)# scheduler task my-compliance-report schedule "0 2 1 * *" \
ha-mode secondary ha-node-id secondary-node1 \
action-name check-compliance action-node /reports

The scheduler is disabled when HA is enabled and when HA mode is NONE. See Mode of Operation in HA for more details.

Troubleshooting

Troubleshooting information is covered below.

History Log

To find out whether a scheduled task has run successfully or not, the easiest way is to view the history log of the scheduler. It will display the latest runs of the scheduled task.

admin# show scheduler task sync history | notab
history history-entry 2017-11-01T02:00:00.55003+00:00 0
 duration  0.15
 succeeded true
history history-entry 2017-12-01T02:00:00.549939+00:00 0
 duration  0.09
 succeeded true
history history-entry 2017-01-01T02:00:00.550128+00:00 0
 duration  0.01
 succeeded false
 info      "Resource device ce0 doesn't exist"

XPath Log

Detailed information from the XPath evaluator can be enabled and made available in the xpath log. Add the following snippet to ncs.conf.

<xpathTraceLog>
  <enabled>true</enabled>
  <filename>./xpath.trace</filename>
</xpathTraceLog>

Devel Log

Error information is written to the development log. The development log is meant to be used as support while developing the application. It is enabled in ncs.conf:

<developer-log>
  <enabled>true</enabled>
  <file>
    <name>./logs/devel.log</name>
     <enabled>true</enabled>
  </file>
</developer-log>
<developer-log-level>trace</developer-log-level>

Suspending the Scheduler

While investigating a failure with a scheduled task or performing maintenance on the system, like upgrading, it might be useful to suspend the scheduler temporarily.

admin# scheduler suspend

When ready the scheduler can be resumed.

admin# scheduler resume