How do I write a Prometheus query that returns the value of a label?
I'm making a Grafana dashboard and want a panel that reports the latest version of our app. The version is reported as a label in the app_version (say) metric like so:
app_version_updated{instance="eu99",version="1.5.0-abcdefg"}
I've tried a number of Prometheus queries to extract the version label as a string from the latest member of this time series, to no effect.
For example, the query
count(app_version_updated) by (version)
returns a {version="1.5.0-abcdefg"} element with a value of 1. When put in a Grafana dashboard in a single value panel, this doesn't display the version string but instead the count value (1).
How can I construct a Prometheus query that returns the version string?
Answer
We recently added support for displaying the serie name as a value in the single stat panel (https://github.com/grafana/grafana/issues/4740). So you have to run our nightly build until we release 4.0.
Just make sure the query returns one serie and you can use the "name" value in the dropdown under Options -> big value.Then you can format the string using the legend formater. Ex {{job}} would return "node" as a serie name.
I hope this answers your question.