// 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 prototyping, 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. func NewExpvarCollector(exports map[string]*prometheus.Desc) prometheus.Collector { … }