Prometheus counters: How to get current value with golang client?

Question

I am using counters to count the number of requests. Is there any way to get current value of a prometheus counter?

My aim is to reuse existing counter without allocating another variable.

Golang prometheus client version is 1.1.0.

Answer 1

It's easy, have a function to fetch Prometheus counter value

import (
    "github.com/prometheus/client_golang/prometheus"
    dto "github.com/prometheus/client_model/go"
    "github.com/prometheus/common/log"
)

func GetCounterValue(metric *prometheus.CounterVec) float64 {
    var m = &dto.Metric{}
    if err := metric.WithLabelValues("label1", "label2").Write(m); err != nil {
        log.Error(err)
        return 0
    }
    return m.Counter.GetValue()
}

Answer 2

Currently there is no way to get the value of a counter in the official Golang implementation.

You can also avoid double counting by incrementing your own counter and use an CounterFunc to collect it.

Note: use integral type and atomic to avoid concurrent access issues

// declare the counter as unsigned int
var requestsCounter uint64 = 0

// register counter in Prometheus collector
prometheus.MustRegister(prometheus.NewCounterFunc(
    prometheus.CounterOpts{
        Name: "requests_total",
        Help: "Counts number of requests",
    },
    func() float64 {
        return float64(atomic.LoadUint64(&requestsCounter))
    }))

// somewhere in your code
atomic.AddUint64(&requestsCounter, 1)