I found the Boundary tool to be fascinating. Watching the flow of data move around the network is a bit counterintuitive because our instincts lead us to ask for as much data as possible. But the sizes of data moving around any significant network is so large that we almost need to start thinking at such a high level.
The Boundary service is priced by the hour. However, the company isn't sharing the rates publicly yet.
Boundary's input and output graphs show which protocols are used to carry the data in the cloud.
Circonus: Monitoring from the ground upWhereas Boundary paints the big picture with one brush, Circonus has a different brush for every color in the rainbow. The core of the system is your collection of "checks"-- that is, a query executed to test the system. The simplest may be loading a URL and tracking how long it takes for the data to arrive. The most complex may be elaborate queries on the database to track back-end performance.
There are a surprisingly large number of checks -- more than several dozen. Some dig into remote processes like databases, and others gather information from third-party sources like Google Analytics. There are even some generic ones that fetch JSON blobs from URLs. The tools typically provide a wizardlike progression of forms that culminate in testing the check before saving it.
Circonus takes the data from these checks and turns them into metrics. My request for a URL, for instance, generated six values ranging from the time it takes for the first byte to arrive to the total number of bytes delivered. The price of your Circonus package will depend upon the number of metrics you store. Some checks deliver more metrics, and you can configure how they store the data.