How do Powershell scheduled job InstanceIds work?

Question

I am trying to manage instances of scheduled jobs using the Job cmdlets such as Get-Job and Wait-Job. I am having problems and have the feeling that I am missing something fundamental.

I have found that I should be importing the PSScheduledJob module if I want to work with scheduled job instances using the Job cmdlets.

NOTE: To use the Job cmdlets on instances of scheduled jobs, the PSScheduledJob module must be imported into the session. To import the PSScheduledJob module, type "Import-Module PSScheduledJob" (without quotation marks) or use any Scheduled Job cmdlet, such as Get-ScheduledJob.

https://technet.microsoft.com/en-us/library/hh850536.aspx

I also found that despite what I expected, the Id property on a job instance does not identify it globally - but rather within a single Powershell session.

The ID is an integer that uniquely identifies the job within the current session. It is easier to remember and to type than the instance ID, but it is unique only within the current session.

https://technet.microsoft.com/en-us/library/hh849693.aspx

The InstanceId is supposed to be globally unique which sounds good...

An instance ID is a GUID that uniquely identifies the job on the computer.

https://technet.microsoft.com/en-us/library/hh849693.aspx

...but I seem to be getting the same job instance returning different InstanceIds. The following script gets the InstanceIds for jobs both directly and via remoting.

Import-Module PSScheduledJob;
$localInstanceIds = ( get-job -Name $jobName).InstanceId.Guid

$remoteInstanceIds = (invoke-command -ComputerName . -ArgumentList $jobName -ScriptBlock {
    param([string]$jobName)

    Import-Module PSScheduledJob;
    (get-job -Name Midwinter.AdviceOS.Reports.SsfsTestA).InstanceId.Guid
})

Compare-Object $localInstanceIds $remoteInstanceIds

Note in the output that there are two jobs returned from each method but that none of the InstanceIds match up.

InputObject                                                      SideIndicator                                                   
-----------                                                      -------------                                                   
780df0f3-bfc1-4fef-80f5-730e8cbcc548                             =>                                                              
44109202-cb9b-43cb-8447-7e48905f10a7                             =>                                                              
4fe8efaa-3107-43cd-a55e-b457b3be5993                             <=                                                              
ad3bac3f-9f80-4ccd-b8d9-60c1b49fcf6a                             <=                                                              

I also found that the scheduled job instances are saved on the file system within the profile of the user that created them.

When you create a scheduled job, Windows Powershell creates a directory for the scheduled job in the $home\AppData\Local\Microsoft\Windows\PowerShell\ScheduledJobs directory on the local computer. The directory name is the same as the job name.

https://technet.microsoft.com/en-us/library/hh849673.aspx

The following script retrieves all of the InstanceIds from the Status.xml files for a given job from within that path and compares them with the InstanceIds returned using the Get-Job cmdlet.

Import-Module PSScheduledJob;
$paths = "C:\Users\$userName\AppData\Local\Microsoft\Windows\PowerShell\ScheduledJobs\$jobName\Output\*\Status.xml";

$namespace = @{ns = 'http://schemas.datacontract.org/2004/07/Microsoft.PowerShell.ScheduledJob'};

$instanceIdsFromFileSystem = (Select-Xml -Path $paths -XPath '/ns:StatusInfo/Status_InstanceId/text()' -Namespace $namespace).Node.Value

$instanceIdsFromCmdlet = (Get-Job -Name $jobName).InstanceId

compare-object $instanceIdsFromFileSystem $instanceIdsFromCmdlet -IncludeEqual

The output again shows no matches.

InputObject                                                      SideIndicator                                                   
-----------                                                      -------------                                                   
4fe8efaa-3107-43cd-a55e-b457b3be5993                             =>                                                              
ad3bac3f-9f80-4ccd-b8d9-60c1b49fcf6a                             =>                                                              
e81731dd-4159-476d-937e-7a066d082eb6                             <=                                                              
5ea34723-ab39-4949-b302-c4be1b1588bb                             <=                                                              

Can somebody please shed some light on this for me?

Answer 1

InstanceId is a GUID that is generated at runtime - it does identify the Job ("globally" on the host, but not universally), but does not identify the Job's contents.

Any Job you execute will have a random GUID assigned, they are not designed to identify any Job persistently across sessions, hosts, or even individual executions. If you execute the same Job twice, they will both have different InstanceId properties. This is by design.

If you want to make a permanent identifier for a Job, you can use the Name property.