xDFSReplicationGroup - Error while comparing array containing $null

[solbirn]

In xDFSReplicationGroup Test-TargetResource the following code can set $ExistingFolders to a @($null) array when the replication group does not yet contain folders. This results in a ParameterBindingValidation exception while subsequently evaluating the Compare-Object just below it.

# Compare the Folders
$ExistingFolders = @((Get-DfsReplicatedFolder @Splat -ErrorAction Stop).FolderName)
if ((Compare-Object `
    -ReferenceObject $Folders `
    -DifferenceObject $ExistingFolders).Count -ne 0)

Error message;

Compare-Object : Cannot bind argument to parameter 'ReferenceObject' because it is null.
    + CategoryInfo          : InvalidData: (:) [Compare-Object], ParameterBindingValidation
   Exception
    + FullyQualifiedErrorId : ParameterArgumentValidationErrorNullNotAllowed,Microsoft.Powe
   rShell.Commands.CompareObjectCommand

Can be resolved with:
$ExistingFolders = @((Get-DfsReplicatedFolder @Splat -ErrorAction Stop).FolderName) | where { $_ -ne $null }

[PlagueHO]

Thanks @solbirn - I'll get this sorted this weekend. Thanks muchly for submitting this.

[PlagueHO]

Hi @solbirn - I'll work on this once this PR is merged (should be over the next few days).

[PlagueHO]

Hi @solbirn - I've been looking into this error and I'm not sure it is caused by this problem. Looking at the error message it is reporting that the ReferenceObject is null - this is the folders you should be passing into the Resource itself - rather than the existing Folders. Are you able to post your config so I can take a look?

[solbirn]

Hi @PlagueHO,

Below is the config. I know this is the issue as I resolved in our environment by using a modified version of xDFS with $nulls removed from $ExisitingFolders, but I try to get you the full error as well.

Configuration DFSRConfig
{
    Param 
    ( 
        [String[]]
        $NodeName = "localhost",
        [Parameter(Mandatory=$true)]
        [ValidateNotNullOrEmpty()]
        [String]
        $GroupName,
        [Parameter(Mandatory=$true)]
        [ValidateNotNullOrEmpty()]
        [String[]]
        $DFSMembers,
        [Parameter(Mandatory=$true)]
        [ValidateNotNullOrEmpty()]
        [PSCredential]
        $Credential,
        [String]
        $DomainName = $env:USERDNSDOMAIN
    )

    Import-DscResource -ModuleName PSDesiredStateConfiguration, xDFS

    Node $NodeName 
    {
        if($DFSMembers.Length -eq 2){
            WaitForAll DomainJoin 
            {
                ResourceName = "[xComputer]JoinDomain"
                NodeName = $NodeName
                RetryIntervalSec = 30
                RetryCount = 0
            }

            WaitForAll WaitDCPromo
            {
                ResourceName = "[xADDomainController]NewDC"
                NodeName = $NodeName
                RetryIntervalSec = 30
                RetryCount = 0
            }
        
            WindowsFeature InstallDFSR
            {
                Name = "FS-DFS-Replication"
                Ensure = "Present"
            }

            WindowsFeature InstallDFSRTools
            {
                Name = "RSAT-DFS-Mgmt-Con"
                Ensure = "Present"
            }

            xDFSReplicationGroup DFSRBackupReplicationGroup
            {
                GroupName = $GroupName
                Description = "$GroupName "
                Ensure = 'Present'
                Members = $DFSMembers
                Folders = 'SharedData','UserData'
                DomainName = $DomainName
                DependsOn = @("[WindowsFeature]InstallDFSR","[WindowsFeature]InstallDFSRTools","[WaitForAll]WaitDCPromo")
            }

            xDFSReplicationGroupConnection DFSRBackupReplicationConnectionSource
            {
                GroupName = $GroupName
                Ensure = 'Present'
                EnsureEnabled = 'Enabled'
                SourceComputerName = $DFSMembers[0]
                DestinationComputerName = $DFSMembers[1]
                DependsOn = '[xDFSReplicationGroup]DFSRBackupReplicationGroup'
            }

            xDFSReplicationGroupConnection DFSRBackupReplicationConnectionDestination
            {
                GroupName = $GroupName
                Ensure = 'Present'
                EnsureEnabled = 'Enabled'
                SourceComputerName = $DFSMembers[1]
                DestinationComputerName = $DFSMembers[0]
                DependsOn = '[xDFSReplicationGroup]DFSRBackupReplicationGroup'
            }

            xDFSReplicationGroupFolder DFSRBackupReplicationFolderSharedData
            {
                GroupName = $GroupName
                FolderName = "SharedData"
                Description = "Site specific shared data"
                DependsOn = '[xDFSReplicationGroup]DFSRBackupReplicationGroup'
            }

            xDFSReplicationGroupFolder DFSRBackupReplicationFolderUserData
            {
                GroupName = $GroupName
                FolderName = "UserData"
                Description = "Site specific user data"
                DependsOn = '[xDFSReplicationGroup]DFSRBackupReplicationGroup'
            }

            xDFSReplicationGroupMembership DFSRBackupReplicationMembershipSharedDataPrimary
            {
                GroupName = $GroupName
                FolderName = 'SharedData'
                ComputerName = $DFSMembers[0]
                ContentPath = 'D:\SharedData'
                PrimaryMember = $true
                DependsOn = '[xDFSReplicationGroupFolder]DFSRBackupReplicationFolderSharedData'
            }

            xDFSReplicationGroupMembership DFSRBackupReplicationMembershipSharedDataSecondary
            {
                GroupName = $GroupName
                FolderName = 'SharedData'
                ComputerName = $DFSMembers[1]
                ContentPath = "D:\$GroupName\SharedData"
                PsDscRunAsCredential = $Credential
                DependsOn = '[xDFSReplicationGroupMembership]DFSRBackupReplicationMembershipSharedDataPrimary'
            }

            xDFSReplicationGroupMembership DFSRBackupReplicationMembershipUserDataPrimary
            {
                GroupName = $GroupName
                FolderName = 'UserData'
                ComputerName = $DFSMembers[0]
                ContentPath = 'D:\UserData'
                PrimaryMember = $true
                DependsOn = '[xDFSReplicationGroupFolder]DFSRBackupReplicationFolderUserData'
            }

            xDFSReplicationGroupMembership DFSRBackupReplicationMembershipUserDataSecondary
            {
                GroupName = $GroupName
                FolderName = 'UserData'
                ComputerName = $DFSMembers[1]
                ContentPath = "D:\$GroupName\UserData"
                PsDscRunAsCredential = $Credential
                DependsOn = '[xDFSReplicationGroupMembership]DFSRBackupReplicationMembershipUserDataPrimary'
            }
        }
    }
}

[PlagueHO]

Oh cool! Thank you @solbirn - that is much appreciated. I'll take a look into this this weekend!

[PlagueHO]

Hi @solbirn - I'm having trouble writing any unit/regression tests that replicate this issue. I'm also having trouble replicating this issue on any WS 2016 DFS servers. I'm a bit worried about making the change above because I'm not actually sure why it would actually work (I might be being dumb though). I've checked through this every way and I do think the error you're seeing might be being caused by something else.

Could you answer the following questions for me to help me solve this:
Are you able to output the verbose logs of applying the above config at all?
What is the array $DFSRMembers being passed in as?
Which version of xDFS you are testing with?
What OS are you applying this on (WS 2012 R2, WS 2016 etc)?

Sorry I haven't managed to figure this out yet.

[murrahjm]

Just ran into this error, though I think I'm hitting the issue around line 630 where it checks for differences in membership. I have a dfs replication group with no existing members, and using DFSReplicationGroup resource to specify two members. The line $existingMembers = @((Get-DfsrMember @replicationGroupParameters -ErrorAction Stop).DnsName) is returning a null value, and rightly so. But the line Compare-Object -ReferenceObject $fqdnMembers -DifferenceObject $existingMembers is throwing the error Cannot bind argument to parameter 'DifferenceObject' because it is null.

My first thought would be to check if either $existingmembers or $fqdnMembers is null before trying to compare them. If either are null then there is a difference and no further comparison is needed.

I suppose if they're both null then it could be the same but not sure there's a use case for ensuring that a replication group has no members.

[PlagueHO]

Hi @murrahjm - do you know the version of Windows Server you are running? I was never able to replicate the issue so wasn't able to confirm if the fix would resolve it or not (e.g. I couldn't write tests to confirm this).

[murrahjm]

I ran into the error against 2012r2 and 2016. Full disclosure, I'm actually calling the resource from an ansible playbook, but it should amount to the same thing since the error comes from compare-object. When I saw it I had just created a new replication group from Powershell with no members or folders or anything, then tried to configure it with the dsc resource vs. creating it all from the resource. On May 18, 2018 6:31 PM, "Daniel Scott-Raynsford" <[email protected]> wrote: Hi @murrahjm <https://github.com/murrahjm> - do you know the version of Windows Server you are running? I was never able to replicate the issue so wasn't able to confirm if the fix would resolve it or not (e.g. I couldn't write tests to confirm this). — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#27 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AQ-wt2NQjpl0sxbPenCnDxv_RDJFuRmfks5tz1nbgaJpZM4NJLSF> .

[PlagueHO]

Hi @murrahjm - it should work being used in an Ansible playbook OK (or at least I'd want it to).

So to confirm, you actually created the replication group as an empty group first with no members or anything manually and then ran the playbook? That is a scenario I didn't actually test so it may indeed cause an error. I'm just in the process of spinning up a DFS environment to do some other testing, so I'll check this scenario.

[murrahjm]

Correct. Completely new group created via Powershell before running the playbook. I forget the exact command but I think it was new-dfsrreplicationgroup or something like that with just a name parameter.

…

On Fri, May 18, 2018, 7:07 PM Daniel Scott-Raynsford < ***@***.***> wrote: Hi @murrahjm <https://github.com/murrahjm> - it should work being used in an Ansible playbook OK (or at least I'd want it to). So to confirm, you actually created the replication group as an empty group first with no members or anything manually and then ran the playbook? That is a scenario I didn't actually test so it may indeed cause an error. I'm just in the process of spinning up a DFS environment to do some other testing, so I'll check this scenario. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#27 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AQ-wt7lUZNcwygekvwQW2UUWLLfUeJghks5tz2IxgaJpZM4NJLSF> .

[murrahjm]

Also I have an update that fixes the null comparison issue if you'd like a pull request. Not sure how it fares against all the other scenarios but it should be relatively benign.

[PlagueHO]

Hi @murrahjm - sure - would be delighted to accept a PR (see https://github.com/PowerShell/DscResources/blob/master/CONTRIBUTING.md). But with a change like this it would be good to validate against the integration tests (https://github.com/PowerShell/DFSDsc/blob/dev/Tests/Integration/MSFT_DFSReplicationGroup.Integration.Tests.ps1). The integration tests do need to be run outside of AppVeyor CI because it needs two DFS server nodes to check against. I'm spinning up a test environment at the moment, so if you can submit your PR I can run some checks against the a real environment.

[PlagueHO]

I can confirm that I can replicate this now by taking a deployed Replication Group and removing all the members from it and then reapplying the config. I'm now going to make @murrahjm changes to my copy and check it resolves the issue without any regression of other functions.