Building More PowerCLI Custom Functions for SRM, Step by Step Walkthrough

One of my colleagues Ken Werneburg recently wrote a great blog post about executing an SRM failover via PowerCLI. Ken does a great job of explaining some of the caveats around this feature and how you would actually make the call using PowerCLI. Looking at the code provided I thought it would be a good candidate for encapsulating in a custom function. I wrote recently about using custom functions to simplify using the SRM API from PowerCLI and I think this use case would be a great example.

In Ken’s example he is coding against the raw API from PowerCLI and you have to deal with code like this:

$RPmoref = … # Set the recovery plan we want to use

# define the recovery plan mode we want to use ('1' is a test)
$RPmode = New-Object VMware.VimAutomation.Srm.Views.SrmRecoveryPlanRecoveryMode
$RPmode.Value__ = 1

# start the test
$RPmoref.Start($RPmode)

While this is not too hard to follow it does require that the user to create recovery mode objects using “magic” numbers in the code. Using custom functions we can hide that away and deliver something much nicer. What I would like us to get to is something like:

Start-RecoveryPlan -RecoveryPlan $Plan -RecoveryMode Test

Or even:

Get-RecoveryPlan -Name 'Failover Site A' | Start-RecoveryPlan

So, how do we get there?

First let’s determine how we want to be able to call the functions and specify the parameters we will accept. Here’s my first crack at this:

<#
.SYNOPSIS
Start a Recovery Plan action like test, recovery, cleanup, etc.

.PARAMETER RecoveryPlan
The recovery plan to start

.PARAMETER RecoveryMode
The recovery mode to invoke on the plan. May be one of "test" (the default), "recovery", "cleanup", and "reprotect"
#>
Function Start-RecoveryPlan () {
    Param(
        [Parameter (Mandatory=$true, ValueFromPipeline=$true)] $RecoveryPlan,
        [VMware.VimAutomation.Srm.Views.SrmRecoveryPlanRecoveryMode] $RecoveryMode = 'Test'
    )

    #TODO
}

<#
.SYNOPSIS
Stop a running Recovery Plan action.

.PARAMETER RecoveryPlan
The recovery plan to stop
#>
Function Stop-RecoveryPlan () {
    Param(
        [Parameter (Mandatory=$true, ValueFromPipeline=$true)] $RecoveryPlan
    )

    #TODO
}

A couple of things to note here. First we can directly use the SrmRecoveryPlanRecoveryMode type when defining the parameter. The PowerCLI team have made this an enum type so we get some nice behavior out of the box in terms of type casting. The second thing to note is that we are going to default to a ‘Test’ operation. I am doing this as I don’t want to get into the scenario where we default to a recovery and someone initiates a disruptive failover instead of a test or cleanup, simply because of a scripting error.

Now we have the outline of the functions let’s try and fill them in a little. First we’ll look at the Start-RecoveryPlan function. For this we want to be able to take in the recovery plan and mode parameters and call the SRM API with that information, maybe with a bit of error checking in there as well. If we take the example from Ken’s blog and put it into our function we should get something like:

Function Start-RecoveryPlan () {
    Param(
        [Parameter (Mandatory=$true, ValueFromPipeline=$true)] $RecoveryPlan,
        [VMware.VimAutomation.Srm.Views.SrmRecoveryPlanRecoveryMode] $RecoveryMode = 'Test'
    )

    # Validate with informative error messages
    $rpinfo = $RecoveryPlan.GetInfo()

    if ($rpinfo.State -eq 'Protecting') {
        throw "This recovery plan action needs to be initiated from the other SRM instance"
    }

    $RecoveryPlan.Start($RecoveryMode)
}

The only real change we have made is to avoid tripping ourselves up by running the recovery plan from the protected site. The API expects the plan to be run from the recovery site so we add a check to ensure the recovery plan state is not in the 'Protecting' state which is the default state a plan is in when seen from the protected site API.

Given that executing a recovery plan could be a disruptive event it makes sense to prompt the user for confirmation before executing the failover. We can do this by annotating our cmdlet with SupportsShouldProcess=$True and checking the value of $pscmdlet.ShouldProcess in our function.

So for one final time let’s put it together for our Start-RecoveryPlan function:

Function Start-RecoveryPlan () {
    [cmdletbinding(SupportsShouldProcess=$True,ConfirmImpact="High")]
    Param(
        [Parameter (Mandatory=$true, ValueFromPipeline=$true)] $RecoveryPlan,
        [VMware.VimAutomation.Srm.Views.SrmRecoveryPlanRecoveryMode] $RecoveryMode = 'Test'
    )

    # Validate with informative error messages
    $rpinfo = $RecoveryPlan.GetInfo()

    # Prompt the user to confirm they want to execute the action
    if ($pscmdlet.ShouldProcess($rpinfo.Name, $RecoveryMode)) {
        if ($rpinfo.State -eq 'Protecting') {
            throw "This recovery plan action needs to be initiated from the other SRM instance"
        }

        $RecoveryPlan.Start($RecoveryMode)
    }
}

We can do similar updates for the corresponding Stop-RecoveryPlan function as well. When we put them together with some of the custom functions we have defined earlier it makes it fairly easy to put together very concise scripts like this:

# First let's connect to VC and both SRM servers
$localvc = …
$un = …
$pw = …
Connect-VIServer -Server $localvc -User $un -Password $pw
Connect-SrmServer -User $un -Password $pw -RemoteUser $un -RemotePassword $pw

#Then let's find a recovery plan and execute a failover

Get-RecoveryPlan -Name '_Manchester Site Failover' | Start-RecoveryPlan -RecoveryMode Failover

As always a picture (or in this case a video) can say a thousand words…

I’ve also shared these functions in my SRM Cmdlets github repository to make it easier to illustrate how you can develop this. As always I’ll reiterate that I am pretty new to PowerShell so if you have any feedback, especially on the scripting style say, please let me know!