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// Copyright 2014 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package prometheus_test
import (
"bytes"
"errors"
"fmt"
"math"
"net/http"
"runtime"
"strings"
"time"
dto "github.com/prometheus/client_model/go"
"github.com/prometheus/common/expfmt"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promhttp"
)
func ExampleGauge() {
opsQueued := prometheus.NewGauge(prometheus.GaugeOpts{
Namespace: "our_company",
Subsystem: "blob_storage",
Name: "ops_queued",
Help: "Number of blob storage operations waiting to be processed.",
})
prometheus.MustRegister(opsQueued)
// 10 operations queued by the goroutine managing incoming requests.
opsQueued.Add(10)
// A worker goroutine has picked up a waiting operation.
opsQueued.Dec()
// And once more...
opsQueued.Dec()
}
func ExampleGaugeVec() {
opsQueued := prometheus.NewGaugeVec(
prometheus.GaugeOpts{
Namespace: "our_company",
Subsystem: "blob_storage",
Name: "ops_queued",
Help: "Number of blob storage operations waiting to be processed, partitioned by user and type.",
},
[]string{
// Which user has requested the operation?
"user",
// Of what type is the operation?
"type",
},
)
prometheus.MustRegister(opsQueued)
// Increase a value using compact (but order-sensitive!) WithLabelValues().
opsQueued.WithLabelValues("bob", "put").Add(4)
// Increase a value with a map using WithLabels. More verbose, but order
// doesn't matter anymore.
opsQueued.With(prometheus.Labels{"type": "delete", "user": "alice"}).Inc()
}
func ExampleGaugeFunc_simple() {
if err := prometheus.Register(prometheus.NewGaugeFunc(
prometheus.GaugeOpts{
Subsystem: "runtime",
Name: "goroutines_count",
Help: "Number of goroutines that currently exist.",
},
func() float64 { return float64(runtime.NumGoroutine()) },
)); err == nil {
fmt.Println("GaugeFunc 'goroutines_count' registered.")
}
// Note that the count of goroutines is a gauge (and not a counter) as
// it can go up and down.
// Output:
// GaugeFunc 'goroutines_count' registered.
}
func ExampleGaugeFunc_constLabels() {
// primaryDB and secondaryDB represent two example *sql.DB connections we want to instrument.
var primaryDB, secondaryDB interface {
Stats() struct{ OpenConnections int }
}
if err := prometheus.Register(prometheus.NewGaugeFunc(
prometheus.GaugeOpts{
Namespace: "mysql",
Name: "connections_open",
Help: "Number of mysql connections open.",
ConstLabels: prometheus.Labels{"destination": "primary"},
},
func() float64 { return float64(primaryDB.Stats().OpenConnections) },
)); err == nil {
fmt.Println(`GaugeFunc 'connections_open' for primary DB connection registered with labels {destination="primary"}`)
}
if err := prometheus.Register(prometheus.NewGaugeFunc(
prometheus.GaugeOpts{
Namespace: "mysql",
Name: "connections_open",
Help: "Number of mysql connections open.",
ConstLabels: prometheus.Labels{"destination": "secondary"},
},
func() float64 { return float64(secondaryDB.Stats().OpenConnections) },
)); err == nil {
fmt.Println(`GaugeFunc 'connections_open' for secondary DB connection registered with labels {destination="secondary"}`)
}
// Note that we can register more than once GaugeFunc with same metric name
// as long as their const labels are consistent.
// Output:
// GaugeFunc 'connections_open' for primary DB connection registered with labels {destination="primary"}
// GaugeFunc 'connections_open' for secondary DB connection registered with labels {destination="secondary"}
}
func ExampleCounterVec() {
httpReqs := prometheus.NewCounterVec(
prometheus.CounterOpts{
Name: "http_requests_total",
Help: "How many HTTP requests processed, partitioned by status code and HTTP method.",
},
[]string{"code", "method"},
)
prometheus.MustRegister(httpReqs)
httpReqs.WithLabelValues("404", "POST").Add(42)
// If you have to access the same set of labels very frequently, it
// might be good to retrieve the metric only once and keep a handle to
// it. But beware of deletion of that metric, see below!
m := httpReqs.WithLabelValues("200", "GET")
for i := 0; i < 1000000; i++ {
m.Inc()
}
// Delete a metric from the vector. If you have previously kept a handle
// to that metric (as above), future updates via that handle will go
// unseen (even if you re-create a metric with the same label set
// later).
httpReqs.DeleteLabelValues("200", "GET")
// Same thing with the more verbose Labels syntax.
httpReqs.Delete(prometheus.Labels{"method": "GET", "code": "200"})
// Just for demonstration, let's check the state of the counter vector
// by registering it with a custom registry and then let it collect the
// metrics.
reg := prometheus.NewRegistry()
reg.MustRegister(httpReqs)
metricFamilies, err := reg.Gather()
if err != nil || len(metricFamilies) != 1 {
panic("unexpected behavior of custom test registry")
}
fmt.Println(toNormalizedJSON(sanitizeMetricFamily(metricFamilies[0])))
// Output:
// {"name":"http_requests_total","help":"How many HTTP requests processed, partitioned by status code and HTTP method.","type":"COUNTER","metric":[{"label":[{"name":"code","value":"404"},{"name":"method","value":"POST"}],"counter":{"value":42,"createdTimestamp":"1970-01-01T00:00:10Z"}}]}
}
func ExampleRegister() {
// Imagine you have a worker pool and want to count the tasks completed.
taskCounter := prometheus.NewCounter(prometheus.CounterOpts{
Subsystem: "worker_pool",
Name: "completed_tasks_total",
Help: "Total number of tasks completed.",
})
// This will register fine.
if err := prometheus.Register(taskCounter); err != nil {
fmt.Println(err)
} else {
fmt.Println("taskCounter registered.")
}
// Don't forget to tell the HTTP server about the Prometheus handler.
// (In a real program, you still need to start the HTTP server...)
http.Handle("/metrics", promhttp.Handler())
// Now you can start workers and give every one of them a pointer to
// taskCounter and let it increment it whenever it completes a task.
taskCounter.Inc() // This has to happen somewhere in the worker code.
// But wait, you want to see how individual workers perform. So you need
// a vector of counters, with one element for each worker.
taskCounterVec := prometheus.NewCounterVec(
prometheus.CounterOpts{
Subsystem: "worker_pool",
Name: "completed_tasks_total",
Help: "Total number of tasks completed.",
},
[]string{"worker_id"},
)
// Registering will fail because we already have a metric of that name.
if err := prometheus.Register(taskCounterVec); err != nil {
fmt.Println("taskCounterVec not registered:", err)
} else {
fmt.Println("taskCounterVec registered.")
}
// To fix, first unregister the old taskCounter.
if prometheus.Unregister(taskCounter) {
fmt.Println("taskCounter unregistered.")
}
// Try registering taskCounterVec again.
if err := prometheus.Register(taskCounterVec); err != nil {
fmt.Println("taskCounterVec not registered:", err)
} else {
fmt.Println("taskCounterVec registered.")
}
// Bummer! Still doesn't work.
// Prometheus will not allow you to ever export metrics with
// inconsistent help strings or label names. After unregistering, the
// unregistered metrics will cease to show up in the /metrics HTTP
// response, but the registry still remembers that those metrics had
// been exported before. For this example, we will now choose a
// different name. (In a real program, you would obviously not export
// the obsolete metric in the first place.)
taskCounterVec = prometheus.NewCounterVec(
prometheus.CounterOpts{
Subsystem: "worker_pool",
Name: "completed_tasks_by_id",
Help: "Total number of tasks completed.",
},
[]string{"worker_id"},
)
if err := prometheus.Register(taskCounterVec); err != nil {
fmt.Println("taskCounterVec not registered:", err)
} else {
fmt.Println("taskCounterVec registered.")
}
// Finally it worked!
// The workers have to tell taskCounterVec their id to increment the
// right element in the metric vector.
taskCounterVec.WithLabelValues("42").Inc() // Code from worker 42.
// Each worker could also keep a reference to their own counter element
// around. Pick the counter at initialization time of the worker.
myCounter := taskCounterVec.WithLabelValues("42") // From worker 42 initialization code.
myCounter.Inc() // Somewhere in the code of that worker.
// Note that something like WithLabelValues("42", "spurious arg") would
// panic (because you have provided too many label values). If you want
// to get an error instead, use GetMetricWithLabelValues(...) instead.
notMyCounter, err := taskCounterVec.GetMetricWithLabelValues("42", "spurious arg")
if err != nil {
fmt.Println("Worker initialization failed:", err)
}
if notMyCounter == nil {
fmt.Println("notMyCounter is nil.")
}
// A different (and somewhat tricky) approach is to use
// ConstLabels. ConstLabels are pairs of label names and label values
// that never change. Each worker creates and registers an own Counter
// instance where the only difference is in the value of the
// ConstLabels. Those Counters can all be registered because the
// different ConstLabel values guarantee that each worker will increment
// a different Counter metric.
counterOpts := prometheus.CounterOpts{
Subsystem: "worker_pool",
Name: "completed_tasks",
Help: "Total number of tasks completed.",
ConstLabels: prometheus.Labels{"worker_id": "42"},
}
taskCounterForWorker42 := prometheus.NewCounter(counterOpts)
if err := prometheus.Register(taskCounterForWorker42); err != nil {
fmt.Println("taskCounterVForWorker42 not registered:", err)
} else {
fmt.Println("taskCounterForWorker42 registered.")
}
// Obviously, in real code, taskCounterForWorker42 would be a member
// variable of a worker struct, and the "42" would be retrieved with a
// GetId() method or something. The Counter would be created and
// registered in the initialization code of the worker.
// For the creation of the next Counter, we can recycle
// counterOpts. Just change the ConstLabels.
counterOpts.ConstLabels = prometheus.Labels{"worker_id": "2001"}
taskCounterForWorker2001 := prometheus.NewCounter(counterOpts)
if err := prometheus.Register(taskCounterForWorker2001); err != nil {
fmt.Println("taskCounterVForWorker2001 not registered:", err)
} else {
fmt.Println("taskCounterForWorker2001 registered.")
}
taskCounterForWorker2001.Inc()
taskCounterForWorker42.Inc()
taskCounterForWorker2001.Inc()
// Yet another approach would be to turn the workers themselves into
// Collectors and register them. See the Collector example for details.
// Output:
// taskCounter registered.
// taskCounterVec not registered: a previously registered descriptor with the same fully-qualified name as Desc{fqName: "worker_pool_completed_tasks_total", help: "Total number of tasks completed.", constLabels: {}, variableLabels: {worker_id}} has different label names or a different help string
// taskCounter unregistered.
// taskCounterVec not registered: a previously registered descriptor with the same fully-qualified name as Desc{fqName: "worker_pool_completed_tasks_total", help: "Total number of tasks completed.", constLabels: {}, variableLabels: {worker_id}} has different label names or a different help string
// taskCounterVec registered.
// Worker initialization failed: inconsistent label cardinality: expected 1 label values but got 2 in []string{"42", "spurious arg"}
// notMyCounter is nil.
// taskCounterForWorker42 registered.
// taskCounterForWorker2001 registered.
}
func ExampleSummary() {
temps := prometheus.NewSummary(prometheus.SummaryOpts{
Name: "pond_temperature_celsius",
Help: "The temperature of the frog pond.",
Objectives: map[float64]float64{0.5: 0.05, 0.9: 0.01, 0.99: 0.001},
})
// Simulate some observations.
for i := 0; i < 1000; i++ {
temps.Observe(30 + math.Floor(120*math.Sin(float64(i)*0.1))/10)
}
// Just for demonstration, let's check the state of the summary by
// (ab)using its Write method (which is usually only used by Prometheus
// internally).
metric := &dto.Metric{}
temps.Write(metric)
fmt.Println(toNormalizedJSON(sanitizeMetric(metric)))
// Output:
// {"summary":{"sampleCount":"1000","sampleSum":29969.50000000001,"quantile":[{"quantile":0.5,"value":31.1},{"quantile":0.9,"value":41.3},{"quantile":0.99,"value":41.9}],"createdTimestamp":"1970-01-01T00:00:10Z"}}
}
func ExampleSummaryVec() {
temps := prometheus.NewSummaryVec(
prometheus.SummaryOpts{
Name: "pond_temperature_celsius",
Help: "The temperature of the frog pond.",
Objectives: map[float64]float64{0.5: 0.05, 0.9: 0.01, 0.99: 0.001},
},
[]string{"species"},
)
// Simulate some observations.
for i := 0; i < 1000; i++ {
temps.WithLabelValues("litoria-caerulea").Observe(30 + math.Floor(120*math.Sin(float64(i)*0.1))/10)
temps.WithLabelValues("lithobates-catesbeianus").Observe(32 + math.Floor(100*math.Cos(float64(i)*0.11))/10)
}
// Create a Summary without any observations.
temps.WithLabelValues("leiopelma-hochstetteri")
// Just for demonstration, let's check the state of the summary vector
// by registering it with a custom registry and then let it collect the
// metrics.
reg := prometheus.NewRegistry()
reg.MustRegister(temps)
metricFamilies, err := reg.Gather()
if err != nil || len(metricFamilies) != 1 {
panic("unexpected behavior of custom test registry")
}
fmt.Println(toNormalizedJSON(sanitizeMetricFamily(metricFamilies[0])))
// Output:
// {"name":"pond_temperature_celsius","help":"The temperature of the frog pond.","type":"SUMMARY","metric":[{"label":[{"name":"species","value":"leiopelma-hochstetteri"}],"summary":{"sampleCount":"0","sampleSum":0,"quantile":[{"quantile":0.5,"value":"NaN"},{"quantile":0.9,"value":"NaN"},{"quantile":0.99,"value":"NaN"}],"createdTimestamp":"1970-01-01T00:00:10Z"}},{"label":[{"name":"species","value":"lithobates-catesbeianus"}],"summary":{"sampleCount":"1000","sampleSum":31956.100000000017,"quantile":[{"quantile":0.5,"value":32.4},{"quantile":0.9,"value":41.4},{"quantile":0.99,"value":41.9}],"createdTimestamp":"1970-01-01T00:00:10Z"}},{"label":[{"name":"species","value":"litoria-caerulea"}],"summary":{"sampleCount":"1000","sampleSum":29969.50000000001,"quantile":[{"quantile":0.5,"value":31.1},{"quantile":0.9,"value":41.3},{"quantile":0.99,"value":41.9}],"createdTimestamp":"1970-01-01T00:00:10Z"}}]}
}
func ExampleNewConstSummary() {
desc := prometheus.NewDesc(
"http_request_duration_seconds",
"A summary of the HTTP request durations.",
[]string{"code", "method"},
prometheus.Labels{"owner": "example"},
)
// Create a constant summary from values we got from a 3rd party telemetry system.
s := prometheus.MustNewConstSummary(
desc,
4711, 403.34,
map[float64]float64{0.5: 42.3, 0.9: 323.3},
"200", "get",
)
// Just for demonstration, let's check the state of the summary by
// (ab)using its Write method (which is usually only used by Prometheus
// internally).
metric := &dto.Metric{}
s.Write(metric)
fmt.Println(toNormalizedJSON(metric))
// Output:
// {"label":[{"name":"code","value":"200"},{"name":"method","value":"get"},{"name":"owner","value":"example"}],"summary":{"sampleCount":"4711","sampleSum":403.34,"quantile":[{"quantile":0.5,"value":42.3},{"quantile":0.9,"value":323.3}]}}
}
func ExampleHistogram() {
temps := prometheus.NewHistogram(prometheus.HistogramOpts{
Name: "pond_temperature_celsius",
Help: "The temperature of the frog pond.", // Sorry, we can't measure how badly it smells.
Buckets: prometheus.LinearBuckets(20, 5, 5), // 5 buckets, each 5 centigrade wide.
})
// Simulate some observations.
for i := 0; i < 1000; i++ {
temps.Observe(30 + math.Floor(120*math.Sin(float64(i)*0.1))/10)
}
// Just for demonstration, let's check the state of the histogram by
// (ab)using its Write method (which is usually only used by Prometheus
// internally).
metric := &dto.Metric{}
temps.Write(metric)
fmt.Println(toNormalizedJSON(sanitizeMetric(metric)))
// Output:
// {"histogram":{"sampleCount":"1000","sampleSum":29969.50000000001,"bucket":[{"cumulativeCount":"192","upperBound":20},{"cumulativeCount":"366","upperBound":25},{"cumulativeCount":"501","upperBound":30},{"cumulativeCount":"638","upperBound":35},{"cumulativeCount":"816","upperBound":40}],"createdTimestamp":"1970-01-01T00:00:10Z"}}
}
func ExampleNewConstHistogram() {
desc := prometheus.NewDesc(
"http_request_duration_seconds",
"A histogram of the HTTP request durations.",
[]string{"code", "method"},
prometheus.Labels{"owner": "example"},
)
// Create a constant histogram from values we got from a 3rd party telemetry system.
h := prometheus.MustNewConstHistogram(
desc,
4711, 403.34,
map[float64]uint64{25: 121, 50: 2403, 100: 3221, 200: 4233},
"200", "get",
)
// Just for demonstration, let's check the state of the histogram by
// (ab)using its Write method (which is usually only used by Prometheus
// internally).
metric := &dto.Metric{}
h.Write(metric)
fmt.Println(toNormalizedJSON(metric))
// Output:
// {"label":[{"name":"code","value":"200"},{"name":"method","value":"get"},{"name":"owner","value":"example"}],"histogram":{"sampleCount":"4711","sampleSum":403.34,"bucket":[{"cumulativeCount":"121","upperBound":25},{"cumulativeCount":"2403","upperBound":50},{"cumulativeCount":"3221","upperBound":100},{"cumulativeCount":"4233","upperBound":200}]}}
}
func ExampleNewConstHistogram_WithExemplar() {
desc := prometheus.NewDesc(
"http_request_duration_seconds",
"A histogram of the HTTP request durations.",
[]string{"code", "method"},
prometheus.Labels{"owner": "example"},
)
// Create a constant histogram from values we got from a 3rd party telemetry system.
h := prometheus.MustNewConstHistogram(
desc,
4711, 403.34,
map[float64]uint64{25: 121, 50: 2403, 100: 3221, 200: 4233},
"200", "get",
)
// Wrap const histogram with exemplars for each bucket.
exemplarTs, _ := time.Parse(time.RFC850, "Monday, 02-Jan-06 15:04:05 GMT")
exemplarLabels := prometheus.Labels{"testName": "testVal"}
h = prometheus.MustNewMetricWithExemplars(
h,
prometheus.Exemplar{Labels: exemplarLabels, Timestamp: exemplarTs, Value: 24.0},
prometheus.Exemplar{Labels: exemplarLabels, Timestamp: exemplarTs, Value: 42.0},
prometheus.Exemplar{Labels: exemplarLabels, Timestamp: exemplarTs, Value: 89.0},
prometheus.Exemplar{Labels: exemplarLabels, Timestamp: exemplarTs, Value: 157.0},
)
// Just for demonstration, let's check the state of the histogram by
// (ab)using its Write method (which is usually only used by Prometheus
// internally).
metric := &dto.Metric{}
h.Write(metric)
fmt.Println(toNormalizedJSON(metric))
// Output:
// {"label":[{"name":"code","value":"200"},{"name":"method","value":"get"},{"name":"owner","value":"example"}],"histogram":{"sampleCount":"4711","sampleSum":403.34,"bucket":[{"cumulativeCount":"121","upperBound":25,"exemplar":{"label":[{"name":"testName","value":"testVal"}],"value":24,"timestamp":"2006-01-02T15:04:05Z"}},{"cumulativeCount":"2403","upperBound":50,"exemplar":{"label":[{"name":"testName","value":"testVal"}],"value":42,"timestamp":"2006-01-02T15:04:05Z"}},{"cumulativeCount":"3221","upperBound":100,"exemplar":{"label":[{"name":"testName","value":"testVal"}],"value":89,"timestamp":"2006-01-02T15:04:05Z"}},{"cumulativeCount":"4233","upperBound":200,"exemplar":{"label":[{"name":"testName","value":"testVal"}],"value":157,"timestamp":"2006-01-02T15:04:05Z"}}]}}
}
func ExampleAlreadyRegisteredError() {
reqCounter := prometheus.NewCounter(prometheus.CounterOpts{
Name: "requests_total",
Help: "The total number of requests served.",
})
if err := prometheus.Register(reqCounter); err != nil {
are := &prometheus.AlreadyRegisteredError{}
if errors.As(err, are) {
// A counter for that metric has been registered before.
// Use the old counter from now on.
reqCounter = are.ExistingCollector.(prometheus.Counter)
} else {
// Something else went wrong!
panic(err)
}
}
reqCounter.Inc()
}
func ExampleGatherers() {
reg := prometheus.NewRegistry()
temp := prometheus.NewGaugeVec(
prometheus.GaugeOpts{
Name: "temperature_kelvin",
Help: "Temperature in Kelvin.",
},
[]string{"location"},
)
reg.MustRegister(temp)
temp.WithLabelValues("outside").Set(273.14)
temp.WithLabelValues("inside").Set(298.44)
var parser expfmt.TextParser
text := `
# TYPE humidity_percent gauge
# HELP humidity_percent Humidity in %.
humidity_percent{location="outside"} 45.4
humidity_percent{location="inside"} 33.2
# TYPE temperature_kelvin gauge
# HELP temperature_kelvin Temperature in Kelvin.
temperature_kelvin{location="somewhere else"} 4.5
`
parseText := func() ([]*dto.MetricFamily, error) {
parsed, err := parser.TextToMetricFamilies(strings.NewReader(text))
if err != nil {
return nil, err
}
var result []*dto.MetricFamily
for _, mf := range parsed {
result = append(result, mf)
}
return result, nil
}
gatherers := prometheus.Gatherers{
reg,
prometheus.GathererFunc(parseText),
}
gathering, err := gatherers.Gather()
if err != nil {
fmt.Println(err)
}
out := &bytes.Buffer{}
for _, mf := range gathering {
if _, err := expfmt.MetricFamilyToText(out, mf); err != nil {
panic(err)
}
}
fmt.Print(out.String())
fmt.Println("----------")
// Note how the temperature_kelvin metric family has been merged from
// different sources. Now try
text = `
# TYPE humidity_percent gauge
# HELP humidity_percent Humidity in %.
humidity_percent{location="outside"} 45.4
humidity_percent{location="inside"} 33.2
# TYPE temperature_kelvin gauge
# HELP temperature_kelvin Temperature in Kelvin.
# Duplicate metric:
temperature_kelvin{location="outside"} 265.3
# Missing location label (note that this is undesirable but valid):
temperature_kelvin 4.5
`
gathering, err = gatherers.Gather()
if err != nil {
// We expect error collected metric "temperature_kelvin" { label:<name:"location" value:"outside" > gauge:<value:265.3 > } was collected before with the same name and label values
// We cannot assert it because of https://github.com/golang/protobuf/issues/1121
if strings.HasPrefix(err.Error(), `collected metric "temperature_kelvin" `) {
fmt.Println("Found duplicated metric `temperature_kelvin`")
} else {
fmt.Print(err)
}
}
// Note that still as many metrics as possible are returned:
out.Reset()
for _, mf := range gathering {
if _, err := expfmt.MetricFamilyToText(out, mf); err != nil {
panic(err)
}
}
fmt.Print(out.String())
// Output:
// # HELP humidity_percent Humidity in %.
// # TYPE humidity_percent gauge
// humidity_percent{location="inside"} 33.2
// humidity_percent{location="outside"} 45.4
// # HELP temperature_kelvin Temperature in Kelvin.
// # TYPE temperature_kelvin gauge
// temperature_kelvin{location="inside"} 298.44
// temperature_kelvin{location="outside"} 273.14
// temperature_kelvin{location="somewhere else"} 4.5
// ----------
// Found duplicated metric `temperature_kelvin`
// # HELP humidity_percent Humidity in %.
// # TYPE humidity_percent gauge
// humidity_percent{location="inside"} 33.2
// humidity_percent{location="outside"} 45.4
// # HELP temperature_kelvin Temperature in Kelvin.
// # TYPE temperature_kelvin gauge
// temperature_kelvin 4.5
// temperature_kelvin{location="inside"} 298.44
// temperature_kelvin{location="outside"} 273.14
}
func ExampleNewMetricWithTimestamp() {
desc := prometheus.NewDesc(
"temperature_kelvin",
"Current temperature in Kelvin.",
nil, nil,
)
// Create a constant gauge from values we got from an external
// temperature reporting system. Those values are reported with a slight
// delay, so we want to add the timestamp of the actual measurement.
temperatureReportedByExternalSystem := 298.15
timeReportedByExternalSystem := time.Date(2009, time.November, 10, 23, 0, 0, 12345678, time.UTC)
s := prometheus.NewMetricWithTimestamp(
timeReportedByExternalSystem,
prometheus.MustNewConstMetric(
desc, prometheus.GaugeValue, temperatureReportedByExternalSystem,
),
)
// Just for demonstration, let's check the state of the gauge by
// (ab)using its Write method (which is usually only used by Prometheus
// internally).
metric := &dto.Metric{}
s.Write(metric)
fmt.Println(toNormalizedJSON(metric))
// Output:
// {"gauge":{"value":298.15},"timestampMs":"1257894000012"}
}
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