Developing a windows service watchdog

2020-07

In a distant past (circa 2011), I had a situation where it was necessary to watchdog a Windows service.
So, I created a VB.NET project of the type console that could be executed on .NET 4.0.

At the time, we decided the watchdog would need to send an email in case the service (usually a Tomcat instance) was found down and that it would try to restart Tomcat in such cases.
So, the following fields were used:

• smtp.server - mail.domain.com
• smtp.port - in general 25
• smtp.useTLS - true or false depending on your SMTP server configuration
• smtp.user - user name
• smtp.password - user password
• email.from - user@domain.com
• email.to - user1@domain.com, user2@domain.com
• email.title - service XYZ is down
• email.content - service XYZ is down since n minuets
• service.Name - tomcat
• sleepTime - time in milliseconds to sleep between checks

Imports System
Imports System.Net
Imports System.Net.Mail
Imports System.ServiceProcess

Module Main

  Sub Main()
    While (True)
      Call CheckService()
      System.Threading.Thread.Sleep(My.Settings.sleeptime)
    End While
  End Sub

  Public Sub SendEmail()
    Dim Message As New Net.Mail.MailMessage()
    Dim FromEmail As New Net.Mail.MailAddress(My.Settings.email.from)
    Message.From = FromEmail
    Message.To.Add(My.Settings.email.to)
    Message.Subject = My.Settings.email.title
    Message.Body = My.Settings.email.content
    Message.Priority = Net.Mail.MailPriority.High

    '587 for gmail, 25 for most...
    Dim SmtpClient As New Net.Mail.SmtpClient(My.Settings.smtp.server,
                                              My.Settings.smtp.port)
    SmtpClient.Send(Message)
  End Sub

  Private Sub CheckService()
    Dim Service As ServiceController
    Dim Services As ServiceController() = ServiceController.GetServices()

    Try
      For Each Service In Services
        'service statuses: ContinuePending, Paused, PausePending, Running, StartPending, Stopped, StopPending
        'Console.WriteLine("service: " + Service.ServiceName.ToString + " status: " + Service.Status.ToString)
        If Service.ServiceName.StartsWith(My.Settings.service.Name)
           And (Service.Status.ToString.StartsWith("Stopped")
                Or Service.Status.ToString.StartsWith("Paused")
                Or Service.Status.ToString.StartsWith("StopPending")
                Or Service.Status.ToString.StartsWith("PausePending")) Then
          SendEmail()
          Service.Start()
          Exit Try
        End If
      Next Service

    Catch ex As Exception
      Console.WriteLine(ex.Message)
    End Try
  End Sub

End Module