expvar

func NewCollector ¶

func NewCollector(exports map[string]*prometheus.Desc) prometheus.Collector

NewExpvarCollector returns a newly allocated expvar Collector.

An expvar Collector collects metrics from the expvar interface. It provides a quick way to expose numeric values that are already exported via expvar as Prometheus metrics. Note that the data models of expvar and Prometheus are fundamentally different, and that the expvar Collector is inherently slower than native Prometheus metrics. Thus, the expvar Collector is probably great for experiments and prototying, but you should seriously consider a more direct implementation of Prometheus metrics for monitoring production systems.

The exports map has the following meaning:

The keys in the map correspond to expvar keys, i.e. for every expvar key you want to export as Prometheus metric, you need an entry in the exports map. The descriptor mapped to each key describes how to export the expvar value. It defines the name and the help string of the Prometheus metric proxying the expvar value. The type will always be Untyped.

For descriptors without variable labels, the expvar value must be a number or a bool. The number is then directly exported as the Prometheus sample value. (For a bool, 'false' translates to 0 and 'true' to 1). Expvar values that are not numbers or bools are silently ignored.

If the descriptor has one variable label, the expvar value must be an expvar map. The keys in the expvar map become the various values of the one Prometheus label. The values in the expvar map must be numbers or bools again as above.

For descriptors with more than one variable label, the expvar must be a nested expvar map, i.e. where the values of the topmost map are maps again etc. until a depth is reached that corresponds to the number of labels. The leaves of that structure must be numbers or bools as above to serve as the sample values.

Anything that does not fit into the scheme above is silently ignored.