The IT ecosystem is rich with network monitoring systems (NMS). Each NMS has different capabilities, costs, and purposes in life. It is commonplace for me to come into a business that has invested in an NMS that doesn’t fit all their needs. You might ask, “What does this have to do with creating a Windows service?” Here is the scenario that brought this up.
A client has a monitoring solution for their Windows servers and some basic network up/down stats. Their internet connection had been flaky for a month or two. As we worked with their ISP, their connection continued to stay up but latency would spike and often drop packets. The monitoring never sees the link as down but the level of service is degraded and mostly unusable. The ISP can quickly reset the ports and fix the issue, but we want to know right when this happens to minimize downtime.
I setup a powershell script with the help of the team at ComputerPerformance. This script is pretty straight forward. It uses the Test-Connection cmdlet and averages the latency to a remote host.
# Gets the average latency between you and $Server
# Using IP Addresses is recommended
$Server = "8.8.8.8"
$PingServer = Test-Connection -count 20 $Server
$Avg = ($PingServer | Measure-Object ResponseTime -average)
$Calc = [System.Math]::Round($Avg.average)
If ($Calc -gt 100 -Or $Calc -eq 0) {stop-service MyService} Else {start-service MyService}Now, for the tricky part. How do I create a service that I can start and stop without actually impacting the underlying OS? I won’t go into the code too much but I have included the example C# source files in a zip at the bottom. I got this code from a MSDN social forum post.
To implement this, first make sure you read the forum post. You will need Visual Studio 2010 C# Express. Create a Windows Form Application and include references (Project –> Add References –> .NET) to System.Configuration.Install and System.ServiceProcess. You will need three files in your project: MyService.cs, MyServiceInstaller.cs and Program.cs. These are included in a zip at the end of this article (I also included the executable from the code if you want to test it out). You really only need to edit the MyService.cs and MyServiceInstaller.cs to match the Service’s purpose in life (and write useful event log entries). Once that is done, build the program. You will get an error on build about a “Windows Service Start Failure” as shown below. (Any developers out there know how to make this build w/o throwing the obvious error?) Just ignore the error and grab the executable from the Debug folder of the project. Place the executable somewhere safe (I use %windir%SysWOW64 in my example below).
Next, we need to install the service. You can install the service using the SC command in Windows. In this example, I used the name “lattest” as the service name and defined the display name as well. You can find more information on the SC.exe command here. Note: those spaces after the equals (=) sign are required when using the SC command. Here is the code I used to install this service on Server 2008 R2:
sc create lattest binpath= "C:\Windows\SysWOW64\MyService.exe" displayname= "Latency Test" start= auto
At this point, your script can be setup to run as a scheduled task to start or stop the service depending on the conditions you set. You can point your NMS to monitor the service and you can sleep peacefully at night knowing you are proactively monitoring the issue.
If this is temporary in nature and you want to remove the service, just remove it from your NMS, delete the service and executable and remove your scheduled task. The service can be removed by running:
sc delete lattest