We have a number of sites in a number of environments. Many of the environments are load balanced with two web servers (and in some cases two app servers). Twice in the past two months we've run into a situation in which a server was inadvertently taken out of the load balancer. This bit us a few days later when the second server was taken out and the site went down completely. In both cases the problem was discovered and corrected quickly, but it leads me to believe that we need an alert when a server is out of the load balancer. Our normal alerts don't work here because in both cases the website on the server was up and responding, it just wasn't in the LB.
It might be possible to set up alerts on the load balancer itself, but they are managed by our hosting provider and dealing with them can be a pain.
My thought is to have an app that scans the server logs every 15 minutes and sends an email when the number of unique visitors per hour drops below a certain threshold. Doesn't sound terribly difficult to write, but seems like there may already be a standard 3rd party tool that already does something along these lines.
We use Windows, ASP.NET, IIS, if that matters.
Recommendation for a tool that alerts when a website is not getting hits?