It is generally desirable to group all the hosts for a specific service into a single dashboard view. For example, all the web servers are in single view while all the database servers are in another view.
This is usually not an issue when you are sending custom metrics using Riemann client. However, there are cases where you are using something that you do not control how the metrics are being sent. i.e., Riemann-tools.
Since Riemann-tools scripts are application agnostic, in order for the dashboard view to group hosts, we must inject some application specific information into the tags field. Tags is a collection of arbitrary strings. In the case of Riemann-tools scripts you can pass in arbitrary strings on the command line.
riemann-health --host 127.0.0.1 --tag "prod" --tag "webserver"