What is the GTMProbe user agent?

I was investigating why a cloud service that was supposed to be unused was receiving traffic, and upon looking at the IIS logs I noticed the majority of the requests were coming from a web client using the following user agent:

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; GTMProbe 1.0)

A quick Google search for ‘gtmprobe’ found an MSDN forum post referring to Azure Traffic Manager. This rang a bell as we had recently set up a Traffic Manager profile for this cloud service to make it the failover for another cloud service.

It seems obvious in retrospect, but after setting up a Traffic Manager profile to your cloud services, start to expect web requests from Traffic Manager to the cloud service every 5 to 10 seconds.

Traffic Manager probes cloud service endpoints and will adjust DNS records to direct traffic to the appropriate cloud service. See the About Traffic Manager Monitoring documentation for information about the probing behavior.