Add clock_time_seconds metric

Fixes: https://github.com/jetstack/cert-manager/issues/3730
Related: https://github.com/jetstack/cert-manager/pull/3746

Signed-off-by: kit837 <66801824+kit837@users.noreply.github.com>

pkg/metrics/metrics.go

@@ -55,6 +55,7 @@ type Metrics struct {
 	log      logr.Logger
 	registry *prometheus.Registry
 
+	clockTimeSeconds                 prometheus.CounterFunc
 	certificateExpiryTimeSeconds     *prometheus.GaugeVec
 	certificateReadyStatus           *prometheus.GaugeVec
 	acmeClientRequestDurationSeconds *prometheus.SummaryVec
@@ -66,6 +67,17 @@ var readyConditionStatuses = [...]cmmeta.ConditionStatus{cmmeta.ConditionTrue, c
 
 func New(log logr.Logger) *Metrics {
 	var (
+		clockTimeSeconds = prometheus.NewCounterFunc(
+			prometheus.CounterOpts{
+				Namespace: namespace,
+				Name:      "clock_time_seconds",
+				Help:      "The clock time given in seconds (from 1970/01/01 UTC).",
+			},
+			func() float64 {
+				return float64(time.Now().Unix())
+			},
+		)
+
 		certificateExpiryTimeSeconds = prometheus.NewGaugeVec(
 			prometheus.GaugeOpts{
 				Namespace: namespace,
@@ -124,6 +136,7 @@ func New(log logr.Logger) *Metrics {
 		log:      log.WithName("metrics"),
 		registry: prometheus.NewRegistry(),
 
+		clockTimeSeconds:                 clockTimeSeconds,
 		certificateExpiryTimeSeconds:     certificateExpiryTimeSeconds,
 		certificateReadyStatus:           certificateReadyStatus,
 		acmeClientRequestCount:           acmeClientRequestCount,
@@ -136,6 +149,7 @@ func New(log logr.Logger) *Metrics {
 
 // Start will register the Prometheus metrics, and start the Prometheus server
 func (m *Metrics) Start(listenAddress string, enablePprof bool) (*http.Server, error) {
+	m.registry.MustRegister(m.clockTimeSeconds)
 	m.registry.MustRegister(m.certificateExpiryTimeSeconds)
 	m.registry.MustRegister(m.certificateReadyStatus)
 	m.registry.MustRegister(m.acmeClientRequestDurationSeconds)

pkg/metrics/metrics_test.go

@@ -0,0 +1,55 @@
+/*
+Copyright 2020 The cert-manager 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 metrics
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus/testutil"
+
+	logtesting "github.com/jetstack/cert-manager/pkg/logs/testing"
+)
+
+func TestClockMetrics(t *testing.T) {
+	type testT struct {
+		expectedFmt string
+	}
+	tests := map[string]testT{
+		"clock time seconds as expected": {
+			expectedFmt: `
+  # HELP certmanager_clock_time_seconds The clock time given in seconds (from 1970/01/01 UTC).
+  # TYPE certmanager_clock_time_seconds counter
+	certmanager_clock_time_seconds %f
+	`,
+		},
+	}
+	for n, test := range tests {
+		t.Run(n, func(t *testing.T) {
+			m := New(logtesting.TestLogger{T: t})
+
+			if err := testutil.CollectAndCompare(m.clockTimeSeconds,
+				strings.NewReader(fmt.Sprintf(test.expectedFmt, float64(time.Now().Unix()))),
+				"certmanager_clock_time_seconds",
+			); err != nil {
+				t.Errorf("unexpected collecting result:\n%s", err)
+			}
+		})
+	}
+}