[Feature]: Output Formatting

[FelixRTU]

Describe the feature request

Hi. Our checks use Prometheus queries that return a floating point number. This works, but especially percentages and time values are hard to interpret, see the given examples.

A format flag for the return values would be great to solve this. It does not have to be as complex as in Grafana, but some basics would be nice.

Formats that would be currently useful to us:

• number (default)
• percent (0-1)
• time (seconds)
• data (bytes [1000 bits])

Examples:
io-usage in percent

certificate expiration in seconds

[martialblog]

Hi, might be a bit tricky since we would have to somehow map these "formats" to the query output via the CLI, if we don't want to introduce a config file, which I would prefer not to do.

@RincewindsHat Do know other plugins that might do something similar?

[RincewindsHat]

In a way yes. Output formatting flags are quite common. Ideally we could deduct the units from the data source, but Prometheus does not store units for the numbers, or am I mislead here?

A simple improvement could be achived by using different number formatting and reduce the significant digits aber the decimal separator to two in the assumption that everything else is probably irrelevant.

From the top of my mind we could change the query syntax in a way which allows specifying a unit, either via an additional option or the possibility to add a unit to a query (I am not firm enough with Prometheus to say whether we can use a symbol as a proper separator)

[martialblog]

Ideally we could deduct the units from the data source, but Prometheus does not store units for the numbers, or am I mislead here

Correct, units are only in the metric name by convention.

Now that I look at it, since the query subcheck is designed to only run a single query, we could just have a CLI flag for it.
When there are multiple series returned, they all have the same unit.

[FelixRTU]

In my case, a CLI flag to set the unit for all returned series would do the job

[martialblog]

I was wondering, isn't that also something that could be solved with PromQL?

Percent: round(node_memory_MemAvailable_bytes / node_memory_MemTotal_bytes * 100)

Seconds into hours: round(node_time_seconds / 60 / 60)

[FelixRTU]

I was wondering, isn't that also something that could be solved with PromQL?

Percent: round(node_memory_MemAvailable_bytes / node_memory_MemTotal_bytes * 100)

Seconds into hours: round(node_time_seconds / 60 / 60)

You're absolutely right about percentages. But it adds some clarification if my check name does not contain the data type.

With time and data values, the issue is that I have to stick to a single unit, like seconds or years. But return values in a query can span across different magnitudes. So if I base a check on seconds but get values ranging from a few seconds to something like 5443200 (9 weeks), I end up needing a calculator to make sense of the bigger ones.

[RincewindsHat]

Conceptually I would go for adding the base unit (Bytes, Time interval, Percent) via parameters, the right scale and order of magnitude could and should be in the code of the plugin side to usefully display stuff without a lot of fiddeling by the operator.

I guess getting the right time scale on the input side could be delegated to the query (meaning if you select "time interval" as a unit, you have to provide the value in seconds).