Friday, 12 November 2010

Remote connection monitoring with PowerShell and IPMonitor

Recently I've been trying to find a way to use a combination of PowerShell and our monitoring system IPMonitor to check connections between two sites.

Picture the scene, three different sites, A, B and C. At site A we have a monitoring system to check various aspects of the services we look after, sites B and C contain various servers, with VPN links joining A to B, A to C and B to C. From A I can check that the VPN links to B and C are up, but what about the link between B and C? That's where I figured PowerShell could come in handy.

After a bit of searching I found the test-command cmdlet which not only allows you to test a connection like you would with ping, but also to specify the source server to test from. After a little tinkering I came up with the following :

$username = ""
$password = ConvertTo-SecureString "" -AsPlainText -Force
$myCred = New-Object System.Management.Automation.PSCredential $username, $password
if (test-connection -computername -source -Credential $myCred -Quiet)
else {"2"}

As you can see, running the script outputs either 1 or 2 depending on the result of the test. Within IPMonitor I then used an External Process Monitor to call the script, compare the script output with the test value (1 obviously), and then display if the connection is up.

The final piece to the puzzle was making the whole thing at least a bit more secure. For the terminally paranoid, having a script sat there containing a server password doesn't really fill you with joy, so I managed to encrypt the password and use that instead. As it turned out though, doing that in conjunction with IPMonitor turned out to be harder than expected, but I'll go into details on that later.

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