Add prometheus metric

CODE_OF_CONDUCT.md

@@ -54,4 +54,3 @@ This Code of Conduct is adapted from the [Contributor Covenant][homepage], versi
 available at https://www.contributor-covenant.org/version/1/4/code-of-conduct.html
 
 [homepage]: https://www.contributor-covenant.org
-

availability.go

@@ -0,0 +1,39 @@
+package health
+
+// AvailabilityStatus expresses the availability of either
+// a component or the whole system.
+type AvailabilityStatus string
+
+const (
+	// StatusUnknown holds the information that the availability
+	// status is not known, because not all checks were executed yet.
+	StatusUnknown AvailabilityStatus = "unknown"
+	// StatusUp holds the information that the system or a component
+	// is up and running.
+	StatusUp AvailabilityStatus = "up"
+	// StatusDown holds the information that the system or a component
+	// down and not available.
+	StatusDown AvailabilityStatus = "down"
+)
+
+func (s AvailabilityStatus) criticality() int {
+	switch s {
+	case StatusDown:
+		return 2
+	case StatusUnknown:
+		return 1
+	default:
+		return 0
+	}
+}
+
+func (s AvailabilityStatus) toPrometheusValue() float64 {
+	switch s {
+	case StatusDown:
+		return 0
+	case StatusUp:
+		return 1
+	default:
+		return 0
+	}
+}

check.go

@@ -5,9 +5,15 @@ import (
 	"fmt"
 	"sync"
 	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 type (
+	metricOptions struct {
+		namespace string
+		enabled   bool
+	}
 	checkerConfig struct {
 		timeout              time.Duration
 		checks               map[string]*Check
@@ -17,14 +23,16 @@ type (
 		interceptors         []Interceptor
 		detailsDisabled      bool
 		autostartDisabled    bool
+		metricOptions        *metricOptions
 	}
 
 	defaultChecker struct {
-		started  bool
-		mtx      sync.Mutex
-		cfg      checkerConfig
-		state    CheckerState
-		endChans []chan *sync.WaitGroup
+		started   bool
+		mtx       sync.Mutex
+		cfg       checkerConfig
+		state     CheckerState
+		endChans  []chan *sync.WaitGroup
+		promGauge *prometheus.GaugeVec
 	}
 
 	checkResult struct {
@@ -114,35 +122,8 @@ type (
 	// InterceptorFunc is an interceptor function that intercepts any call to
 	// a components health check function.
 	InterceptorFunc func(ctx context.Context, name string, state CheckState) CheckState
-
-	// AvailabilityStatus expresses the availability of either
-	// a component or the whole system.
-	AvailabilityStatus string
 )
 
-const (
-	// StatusUnknown holds the information that the availability
-	// status is not known, because not all checks were executed yet.
-	StatusUnknown AvailabilityStatus = "unknown"
-	// StatusUp holds the information that the system or a component
-	// is up and running.
-	StatusUp AvailabilityStatus = "up"
-	// StatusDown holds the information that the system or a component
-	// down and not available.
-	StatusDown AvailabilityStatus = "down"
-)
-
-func (s AvailabilityStatus) criticality() int {
-	switch s {
-	case StatusDown:
-		return 2
-	case StatusUnknown:
-		return 1
-	default:
-		return 0
-	}
-}
-
 func newDefaultChecker(cfg checkerConfig) *defaultChecker {
 	checkState := map[string]CheckState{}
 	for _, check := range cfg.checks {
@@ -154,7 +135,20 @@ func newDefaultChecker(cfg checkerConfig) *defaultChecker {
 		state:    CheckerState{Status: StatusUnknown, CheckState: checkState},
 		endChans: []chan *sync.WaitGroup{},
 	}
-
+	if cfg.metricOptions != nil && cfg.metricOptions.enabled {
+		gaugeOpts := prometheus.GaugeOpts{
+			Name: "check_state",
+			Help: "status of each check",
+		}
+		if cfg.metricOptions.namespace != "" {
+			gaugeOpts.Namespace = cfg.metricOptions.namespace
+		}
+		resultGauge := prometheus.NewGaugeVec(
+			gaugeOpts, []string{"name"},
+		)
+		prometheus.MustRegister(resultGauge)
+		checker.promGauge = resultGauge
+	}
 	if !cfg.autostartDisabled {
 		checker.Start()
 	}
@@ -306,6 +300,9 @@ func (ck *defaultChecker) mapStateToCheckerResult() CheckerResult {
 				Error:     toErrorDesc(checkState.Result, ck.cfg.maxErrMsgLen),
 				Timestamp: checkState.LastCheckedAt,
 			}
+			if ck.promGauge != nil {
+				ck.promGauge.WithLabelValues(c.Name).Set(float64(checkState.Status.toPrometheusValue()))
+			}
 		}
 	}
 

config.go

@@ -193,3 +193,13 @@ func WithInterceptors(interceptors ...Interceptor) CheckerOption {
 		cfg.interceptors = interceptors
 	}
 }
+
+// WithMetrics will enable prometheus metrics
+func WithMetrics(namespace string) CheckerOption {
+	return func(cfg *checkerConfig) {
+		cfg.metricOptions = &metricOptions{
+			enabled:   true,
+			namespace: namespace,
+		}
+	}
+}

go.mod

@@ -1,5 +1,22 @@
 module github.com/alexliesenfeld/health
 
-go 1.13
+go 1.19
 
 require github.com/stretchr/testify v1.8.0
+
+require (
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.1.2 // indirect
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/golang/protobuf v1.5.2 // indirect
+	github.com/matttproud/golang_protobuf_extensions v1.0.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/prometheus/client_golang v1.13.0 // indirect
+	github.com/prometheus/client_model v0.2.0 // indirect
+	github.com/prometheus/common v0.37.0 // indirect
+	github.com/prometheus/procfs v0.8.0 // indirect
+	github.com/stretchr/objx v0.4.0 // indirect
+	golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a // indirect
+	google.golang.org/protobuf v1.28.1 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)