Specifying Meta Data for a Measurement

Add the ability to optionally add name/value pairs to a measurement when it is created in Monasca. The name/value pairs can be read from the API when the measurement is read. The value of the measurement will still be required so statistics such as Average, Max, etc. for the metric can be computed. The name/value pairs will be ignored when statistics are requested. At least at first, Alarms won’t be able to be generated on the name/value pairs as that will require a change to the Alarm Definition syntax.

Example:
http_status{url: http://localhost:8080/healthcheck, hostname=devstack, service=object-storage}

Today this returns a single value of either 1 or 0 depending if the status check succeeded. If it fails, it would be helpful to have the actual http status code and error message if possible. So instead of just a value, the measurement would be something like:
{Timestamp=now(), value=0, value_meta{http_rc=500, error_msg=“Error accessing MySQL”}}

When to use them:
   1. Add extra information to a measurement

When not to use them:
    1. When the extra information would be something that should be alarmed on or graphed. For example, we could add response time to http_status, but that would be better as its own metric so it can be graphed and alarmed on

In the future, it may be possible to alarm on the value of one name/value pairs