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Scope

  • JobScheduler Agents support PowerShell for implementation of jobs, see  JS-1595 - Getting issue details... STATUS
  • The support for PowerShell fills the gap between Shell jobs and API jobs:.
    • PowerShell jobs can use any Windows commands or PowerShell cmdlets and functions.
    • PowerShell jobs can use the objects and methods of the JobScheduler API for PowerShell.
  • Some minor differences exist between classic Shell jobs and PowerShell jobs, see Compatibility between PowerShell and Shell.
  • PowerShell jobs are executed with Agents, not with a JobScheduler Master.

Background

  • From the early days of JobScheduler the distinction between Shell jobs and API jobs was introduced:
    • Shell jobs include whatever can be executed from the command line of the respective shell (Unix or Windows)
    • API jobs are coded in a programming/scripting language. JobScheduler exposes its API to supported languages.
  • With PowerShell jobs such differences are leveled in a way that PowerShell jobs can include 
    • commands such as
      • any calls to Windows commands and programs
      • any PowerShell cmdlets
      • any calls to .NET classes
    • callback functions such as spooler_init(), spooler_open(), spooler_process(), spooler_close(), spooler_exit() as known from API jobs:
      • without a callback function being specified script code is automatically executed within the scope of a spooler_process() callback function.
  • At the time of writing performance penalties are obseved for PowerShell jobs due to loading the .NET Framework for the PowerShell run-tme: 
    • the delay for PowerShell jobs starting compared to Shell job is about 1-2s. The effective delay depends on the users system performance.
    • this delay corresponds more or less to the time required to execute PowerShell.exe from the command line.

Feature Availability

FEATURE AVAILABILITY STARTING FROM RELEASE 1.10.5

Examples

For use of the following examples create a process class configuration that points to an Agent running on the same or on a different server. The configuration for a process class my_Agent.process_class.xml could look like this:

Simple process class configuration
<?xml version="1.0" encoding="ISO-8859-1"?>
<process_class  max_processes="10" remote_scheduler="http://localhost:4445"/>

Example: PowerShell Job

Example: A simple PowerShell job with some scripting similar to shell jobs might look like this:

Simple PowerShell Job
<?xml version="1.0" encoding="ISO-8859-1"?>
<job process_class="my_Agent">
    <script language="powershell">
        <![CDATA[
echo "job is starting"

# pause the job for 10 seconds
Start-Sleep -Seconds 10

# list files in a directory
$files = dir *
echo $files
 
# execute some Windows command script
/tmp/some_batch_script.cmd
echo "job is finishing"
        ]]>
    </script>
    <run_time />
</job>


Example: A basic PowerShell job including the call to a function might look like this:

PowerShell Job with user defined function
<?xml version="1.0" encoding="ISO-8859-1"?>
<job  process_class="my_Agent">
    <script  language="powershell">
        <![CDATA[
# PowerShell function used in main job
function Get-Files( $directory )
{
	echo "entering function get_files"
	return Get-ChildItem $directory
}
	
echo "job is starting"
Start-Sleep -Seconds 10
 
$files = Get-Files "c:\tmp\my_directory"
echo $files
echo "job is finishing"	
        ]]>
    </script>
    <run_time />
</job>

Example: PowerShell API Job

A basic API job might look like this:

PowerShell Job with API methods
<?xml version="1.0" encoding="ISO-8859-1"?>
<job  process_class="/tests/Agent" stop_on_error="no">
    <script  language="powershell">
        <![CDATA[
function spooler_process()
{		
	# set variables to store the information about job and task 	
	$jobName = $spooler_job.name()
	$jobTitle = $spooler_job.title()
	$taskId = $spooler_task.id()
	
	# display the information about job and task
	echo "job $jobName with title $jobTitle is starting"
	echo "task ID is $taskId"
		
	echo "job is finishing"
		
	# for standalone jobs set return code to false / for order jobs set to true in case of successful execution
	return $false
}
        ]]>
    </script>
    <run_time />
</job>

Example: Combine both PowerShell Job and Monitor

This PowerShell sample job implements a  pre-processing Monitor script that is executed before the job script is executed:

PowerShell Job with pre-processing Monitor
<?xml version="1.0" encoding="ISO-8859-1"?>
<job  process_class="my_Agent">
    <script  language="powershell">
        <![CDATA[
echo "job is starting"
Start-Sleep -Seconds 10
echo "job is finishing"
        ]]>
    </script>

    <monitor  name="process_powershell" ordering="0">
        <script  language="powershell">
            <![CDATA[
function spooler_process_before()
{
	# check for a "go" file that is required to start the job
	$rc = ( Test-Path -Path "/tmp/go.txt" -PathType Leaf )
	echo ".. looking up go file: $rc"
	return $rc
}
            ]]>
        </script>
    </monitor>

    <run_time />
</job>

Explanations

  • The monitor script is executed before a task is started for this job.
  • Its purpose is to decide if the task should be started or not. This decision is taken from the existence of the file /tmp/go.txt.
  • The return code reflects the decision to start or not to start a task for the job.

Example: PowerShell Job with different output channels

The following sample job explains how to use output channels for PowerShell such as:

 

PowerShell Job with different output channels
<?xml version="1.0" encoding="ISO-8859-1"?>
<job  process_class="my_Agent" stop_on_error="no">
    <settings >
        <log_level ><![CDATA[debug1]]></log_level>
    </settings>

    <script  language="powershell">
        <![CDATA[
# Use Write-Host, Write-Output or Echo cmdlets to write to the JobScheduler log
Write-Host "job: this is some output"
Write-Output "job: this is some output"
echo "job: this is some output"

# Standard PowerShell verbose setting is considered for log output
$VerbosePreference = "Continue"
# In addition the current log level of the job has to be set, i.e. log level "debug1" or higher logs verbose output
Write-Verbose "job: this is some verbose output"

# Standard PowerShell debug setting is considered for log output
$DebugPreference = "Continue"
# In addition the current log level of the job has to be set, i.e. log level "debug3" or higher logs debug messages
Write-Debug "job: this is some debug output"

# creates a warning for the job
Write-Warning "job: this is a warning"

# can be used to throw an error
Write-Error "job: this is an error"
        ]]>
    </script>

    <run_time />
</job>

Explanations

  1. Using PowerShell standard output
    • Use of the Write-HostWrite-Output and Echo cmdlets is applicable.
  2. Using PowerShell verbose output
    • The standard PowerShell verbosity setting is considered for log output if the job is configured for a log level debug1 or higher.
    • Use $VerbosePreference = "Continue" 
    • Subsequently use the Write-Verbose cmdlet.
  3. Using PowerShell debug messages
    • The PowerShell debug setting is considered for log output in jobs if the job is configured for a log level debug3 or higher.
    • Use $DebugPreference = "Continue"
    • Subsequently use the Write-Debug cmdlet.
  4. Using PowerShell Warnings
    • Warnings are created by use of the Write-Warning cmdlet. Such warnings cause corresponding warnings in the JobScheduler Master that are visible from the log and that might trigger a notification by e-mail.
  5. Using PowerShell Error Messages
    • Use of the Write-Error cmdlet will raise a job error that is visible from the log and that triggers subsequent actions as e.g. notification by e-mail, stopping the job, suspending an order etc. 

JobScheduler PowerShell CLI for Jobs

  • The feature is only available in case your Agent is running on a machine with PowerShell available
  • For more information about how to install and to use the JobScheduler PowerShell CLI module for an Agent see PowerShell Command Line Interface - Introduction

 

The JobScheduler PowerShell CLI module is available for PowerShell jobs. A basic job using the PowerShell CLI might look like this:

PowerShell Job with CLI cmdlets
<?xml version="1.0" encoding="ISO-8859-1"?>
<job process_class="my_Agent">
	<script language="powershell">
		<![CDATA[
Import-Module JobScheduler
 
# display summary information
Show-Status
 
# retrieve the number of available job chains
( Get-JobChain ).count

# get the number of current tasks
( Get-Task ).count
		]]>
	</script>
	<run_time />
</job>

Explanations

  • The PowerShell CLI is activated by the Import-Module JobScheduler command.
  • For a complete list of cmdlets available from the PowerShell CLI see PowerShell CLI - Cmdlets

Additional examples are available from the PowerShell CLI - Use Cases article.

Parameter Handling

Reading Order parameters or Job parameters

PowerShell jobs offer additional methods for reading parameters:

PowerShell samples for parameter handling
# Example PowerShell solution 1: environment variable for task/order parameter
$env:SCHEDULER_PARAM_NAME1
 
# Example PowerShell solution 2: shorthand notation for task/order parameter
$spooler_params.get( "name1" )
$spooler_params.value( "name1" )

# Example PowerShell solution 3 - read all task/order parameters as Variable_set
$variableSet = $spooler_params.getAll()

# Example PowerShell solution 4 - read all task/order parameters as object
$parameters = $spooler_params.items
$parameters.name1 
 
# Example PowerShell solution 5: access task parameter
$spooler_task.params().value( "name1" )

# Example PowerShell solution 6: access order parameter
$spooler_task.order().params().value( "name1" )

Explanations

  • Parameter passing by environment variables is only available for PowerShell jobs that do not implement any of the API functions spooler_init(), spooler_exit(), spooler_process() etc.
    • Solution 1
      • $env:SCHEDULER_PARAM_NAME1 returns the respective parameter
  • A new object $spooler_params has been introduced 
    • The objects includes parameters from both job and order. For parameters with the same name an order parameter beats a job parameter.
    • The object includes the following methods:
      • Solution 2
        • $spooler_params.get( "name1" ) reads a parameter value
        • $spooler_params.value( "name1" ) is an alias for $spooler_params.get()
      • Solution 3
        • $spooler_params.getAll() returns a Variable_set with all job and order parameters.
      • Solution 4
        • $parameters = $spooler_params.items returns a PSObject that allows to access individual parameters as PowerShell properties
        • $parameters.name1 returns the parameter "name1" as property
  • The  usual API methods for parameters access are available:
    • Solution 5
      • $spooler_task.params().value( "name1" ) reads a job parameter

    • Solution 6
      • $spooler_task.order().params().value( "name1" ) reads an order parameter

Returning a parameter and its value to an Order or Job

Additionals methods are available for returning parameter values:

PowerShell sample for returning parameter values
# Example PowerShell solution 1: set task/order parameter 
$spooler_params.set( "name1", "value2" )
 
# Example PowerShell solution 2: setting a task parameter 
$spooler_task.params().set_value( "name1", "value2" )

# Example PowerShell solution 3: setting an order parameter
$spooler_task.order().params().set_value( "name1", "value2" )

Explanations

  • Parameters are return
    • Solution 1
      • $spooler_params.set( "name1", "value2" ) 
        • sets a job parameter if the current job is configured as a standalone job
        • sets an order parameter if the current job is configured for a job chain.
    • Solution 2
      • $spooler_task.params().set_value( "name1", "value2" ) sets a parameter for a job (for instance parameter name1 with the initial value value1) and modifies the value to value2
    • Solution 3
      • $spooler_task.order().params().set_value( "name1", "value2" ) sets a parameter for an order (for instance parameter name1 with the initial value value1) and modifies the value to value2

Compatibility between PowerShell and Shell

PowerShell jobs can be considered as a migration path for shell jobs. This suggests that any shell job can possibly be converted (with a few changes) to a PowerShell job. 

Please consider compatibility issues as explained below.

Reading Order parameters or Job parameters

Reading parameters works slightly different for PowerShell jobs than for shell jobs, using $env:VARIABLE for PowerShell instead of %VARIABLE% as for shell:

# Example Shell: environment variable for task/order parameter
myscript.cmd %SCHEDULER_PARAM_NAME1%

# Example PowerShell solution 1: environment variable for task/order parameter
myscript.cmd $env:SCHEDULER_PARAM_NAME1
 
# Example PowerShell solution 2: shorthand notation for task/order parameter
myscript.cmd $spooler_params.get( "name1" )
myscript.cmd $spooler_params.value( "name1" )

Returning a parameter and its value to an Order

Setting a parameter for an order (for instance parameter name1 with the initial value value1) and modifying the value to value2 and returning the parameter to the order so that the next job chain node uses the new value. For PowerShell this works using the API method available from $spooler_task.order():

# Example Shell: 
echo name1 = value2 >> %SCHEDULER_RETURN_VALUES%

# Example PowerShell solution 1: 
$spooler_task.order().params().set_value( "name1", "value2" )
# Example PowerShell solution 2: shorthand notation for task/order parameter 
$spooler_params.set( "name1", "value2" )

Execution Policies

By default PowerShell ships with the execution policy Restricted that does not allow to run scripts from files.

Should jobs be able to run external PowerShell script files then the execution policy has to be modified. This can be performed

  • at machine level, e.g. if an administrator executes Set-ExecutionPolicy RemoteSigned
  • at user level if the the user executes Set-ExecutionPolicy bypass -scope CurrentUser
  • at process level if the the user executes Set-ExecutionPolicy bypass -scope process

Should execution policies not be explicitely ruled for a scheduling environment then we recommend to add Set-ExecutionPolicy bypass -scope process to the profile.

Profile Handling

FEATURE AVAILABILITY STARTING FROM RELEASE 1.11.5

Profile Locations

JobScheduler handles PowerShell profiles in a similar way to the PowerShell host. 

  • The $PROFILE variable returns a collection of locations that a profile is looked up for. By default PowerShell would use four variables as stated below that are mapped by JobScheduler to two possible profile locations.
  • If a profile is found in a number of locations then all profiles are processed in the sequence as stated below. 

Profile locations (<agent_data> points to the data directory that is configured for an Agent, usually by use of the SCHEDULER_DATA environment variable with the Agent instance script):

  • $PROFILE.AllUsersAllHosts, $PROFILE.AllUsersCurrentHost
    • <agent_data>\config\powershell\JobScheduler.PowerShell_profile.ps1
  • $PROFILE.CurrentUserAllHosts, $PROFILE.CurrentUserCurrentHost
    • Agent/Job runs as system account: the same profile as stated above is processed
      • <agent_data>\config\powershell\JobScheduler.PowerShell_profile.ps1
    • Agent/Job runs as user account: the profile is looked up in the Users sub-directory for the current user (indicated by <user_name>).
      • <agent_data>\config\Users\<user_name>\powershell\JobScheduler.PowerShell_profile.ps1

For details check  JS-1746 - Getting issue details... STATUS

Use of Profiles

Profiles can be used

  • to specify alias names for cmdlets,
  • to specify global variables, e.g. paths, that can be used by all jobs,
  • to import PowerShell modules, e.g. to specify Import-Module JobScheduler for use of the PowerShell CLI
  • to specify the behavior in case of errors by use of the $ErrorActionPreference variable
    • A value $ErrorActionPreference = "Continue" (Default) allows a PowerShell script to continue after an error occurred. It is up to the script developer to check for errors, e.g. by use of exceptions.
    • A value $ErrorActionPreference = "Stop" is the recommended setting as it immediately stops execution of the script after an error occurred.

Error Handling

PowerShell jobs offer a number of options to detect run-time errors.

Error handling by JobScheduler

Checking the exit code of PowerShell script

  • PowerShell scripts can use the exit() function to stop execution and to signal the execution result by specifying
    • exit(0) for successful execution
    • exit(1) or any non-zero numeric value
  • JobScheduler will report the value of the exit() function as the job execution result.

Checking the last exit code of a Windows program or script

  • If a native Windows program or script (.bat, .cmd) causes an error then this will assign the exit code to the $LastExitCode global variable. 
    • If a number of programs/scripts are executed from a PowerShell job then the result of the last program/script will decide about the exit code stored with $LastExitCode.
    • This behavior does not apply to cmdlets causing errors.
    • The behavior to stop script execution in case of an error by use of the $ErrorActionPreference does not apply to errors caused by programs/scripts but to PowerShell commands and cmdlets only.
  • JobScheduler checks this variable and will set the job exit code accordingly. For exit codes != 0 an error is raised.
  • This behavior is superior compared to shell jobs as errors from any line in the job script are detected. For shell scripts only the last line of a job script determines the execution result (Unix: $?, Windows: %ERRORLEVEL%).

Checking error output

  • Native Windows programs or scripts and cmdlets can cause errors that create some error output (stderr). 
  • PowerShell jobs can be configured to handle any output found in stderr to indicate an error. Not all output to stderr may indicate an error as a number of Windows native programs is reported to write to stderr instead of stdout. Therefore users can choose from the following configuration:
    • <job stderr_log_level="error"/>
      • Indicates that any output found in stderr will result in a job error.
    • <job stderr_log_level="info"/>
      • Indicates that output to stderr is logged but will not result in a job error (default).
  • Users should consider that output checking is performed after the job has completed. It can therefore not be used to stop execution of a script in case of error, however, we recommend to use output checking that would set the execution result of jobs in case of errors that are not handled by the script.
  • For details check  JS-1329 - Getting issue details... STATUS  and  JS-1393 - Getting issue details... STATUS

Error handling by job scripts

Checking cmdlet errors

  • By default PowerShell most cmdlets write errors to the stderr output channel that is captured by JobScheduler.
    • This does not include that a processing error is raised as in this situation the next line of the PowerShell job script would be executed.
  • Users can force PowerShell to throw an exeception in case of cmdlet errors
    • by setting the global variable $ErrorActionPreference = "Stop". This would stop processing immediately and prevent subsequent lines of the PowerShell job script from being executed. The value of this variable will be considered in case of cmdlet errors and in case of syntax errors, e.g. when using wrong parameterization for cmdlets. JobScheduler will detect this type of error. It is recommended to set this variable in the PowerShell Profile, see chapter Profile Handling.
    • by setting the -ErrorAction stop parameter provided that the cmdlet supports common parameters. The -ErrorAction parameter is not considered for syntax errors when using cmdlets, e.g. in case of wrong parameterization.

Suppressing Exit Codes

  • Users who wish to suppress exit codes of failed executions of native Windows programs or scripts can use
    • $Global:LastExitCode = $null
  • This will disable the above mentioned check of the last exit code.

Catching errors

  • Users can use try/catch blocks to implement individual error handling
    • This simple example prevents errors from being raised for non-accessible network shares:

      try {
      	$found = Test-Path \\some_share\some_directory\some_file -PathType Leaf
      } catch {
      	$found = $false
      }
    • From the above example an exception is raised and handled that does not result in a job error. In addition no output to stderr is created that would be detected by the above mentioned error output checking.

References

Reference Documentation

  • For further information about how to write API Jobs in PowerShell please check the Reference Documentation. You will find the available objects and methods as well as some useful examples for API jobs

Change Management References

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