feat(healthcheck): Add better exporter health check

Better logic around the exporter health.

Related #110

Signed-off-by: oluwole fadeyi <[email protected]>

pkg/barrier/barrier.go

@@ -0,0 +1,64 @@
+package barrier
+
+import (
+	"context"
+	"github.com/juju/errors"
+	"sync"
+	"time"
+)
+
+type (
+	Barrier struct {
+		Capacity     int
+		Value        int
+		RefillPeriod time.Duration
+		mutex        sync.RWMutex
+	}
+)
+
+func New(cap int, rate time.Duration) *Barrier {
+	return &Barrier{
+		Capacity:     cap,
+		Value:        cap,
+		RefillPeriod: rate,
+	}
+}
+
+func (b *Barrier) RecordBadEvent() {
+	b.mutex.Lock()
+	defer b.mutex.Unlock()
+	if b.Value <= 0 {
+		return
+	}
+	b.Value = b.Value - 1
+}
+
+func (b *Barrier) IsBadState() bool {
+	b.mutex.Lock()
+	defer b.mutex.Unlock()
+	return b.Value == 0
+}
+
+func (b *Barrier) refill() {
+	b.mutex.Lock()
+	defer b.mutex.Unlock()
+	if b.Value == b.Capacity {
+		return
+	}
+	b.Value = b.Value + 1
+}
+
+func (b *Barrier) Start(ctx context.Context) error {
+	if b.Value < 0 {
+		return errors.New("The instance cannot be initialised with a negative number")
+	}
+
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		case <-time.Tick(b.RefillPeriod):
+			b.refill()
+		}
+	}
+}

pkg/barrier/barrier_test.go

@@ -0,0 +1,46 @@
+package barrier
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestBarrier(t *testing.T) {
+	t.Parallel()
+	t.Run("successfully record bad event", func(t *testing.T) {
+		b := New(10, 1*time.Second)
+		b.RecordBadEvent()
+		assert.Equal(t, 9, b.Value)
+	})
+	t.Run("errors if the instance capacity is set to a negative number", func(t *testing.T) {
+		ctx := context.Background()
+		b := New(-1, 1*time.Second)
+		assert.Error(t, b.Start(ctx))
+	})
+	t.Run("record bad event doesn't go to a negative number", func(t *testing.T) {
+		b := New(0, 1*time.Second)
+		b.RecordBadEvent()
+		assert.Equal(t, 0, b.Value)
+	})
+	t.Run("isBadState returns true when instance reaches 0", func(t *testing.T) {
+		b := New(0, 1*time.Second)
+		assert.True(t, true, b.IsBadState())
+	})
+	t.Run("successfully refill barrier at the refill rate", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		b := New(10, 1*time.Second)
+		go func() {
+			require.NoError(t, b.Start(ctx))
+		}()
+		b.RecordBadEvent()
+		b.RecordBadEvent()
+		assert.Equal(t, 8, b.Value)
+		time.Sleep(3 * time.Second)
+		cancel()
+		assert.Equal(t, 10, b.Value)
+	})
+}

pkg/exporter/exporter.go

@@ -10,6 +10,7 @@ import (
 	"github.com/labstack/echo/v4"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"github.com/tfadeyi/auth0-simple-exporter/pkg/barrier"
 	"github.com/tfadeyi/auth0-simple-exporter/pkg/client"
 	"github.com/tfadeyi/auth0-simple-exporter/pkg/client/logs"
 	"github.com/tfadeyi/auth0-simple-exporter/pkg/exporter/metrics"
@@ -28,6 +29,8 @@ type (
 		// exporter
 		namespace string
 		subsystem string
+		// detects whether the exporter is in a bad state
+		state *barrier.Barrier
 		// checkpoint from where to start fetching logs
 		startTime          time.Time
 		userMetricDisabled bool
@@ -63,6 +66,7 @@ func New(ctx context.Context, opts ...Option) *exporter {
 		namespace: "auth0",
 		subsystem: "",
 		ctx:       ctx,
+		state:     barrier.New(10, 5*time.Minute),
 		startTime: time.Now(),
 		targetScrapeRequestErrors: prometheus.NewCounter(
 			prometheus.CounterOpts{
@@ -149,6 +153,7 @@ func (e *exporter) collect(ctx context.Context, m *metrics.Metrics) error {
 		eventLogs := list.([]*management.Log)
 		e.logger.V(0).Error(err, "Request was terminated by Prometheus. The exporter could not finish polling the Auth0 log client to fetch the tenant logs."+
 			"Please try increase the prometheus scrape period", "logs_events_found", len(eventLogs), "from", e.startTime)
+		e.state.RecordBadEvent()
 	case errors.Is(err, context.DeadlineExceeded):
 		eventLogs := list.([]*management.Log)
 		e.logger.V(0).Error(err, "Request could not be completed in the current request timeout. The exporter could not finish polling the Auth0 log client to fetch the tenant logs."+
@@ -182,6 +187,7 @@ func (e *exporter) collect(ctx context.Context, m *metrics.Metrics) error {
 			eventUsers := list.([]*management.User)
 			e.logger.V(0).Error(err, "Request was terminated by Prometheus. The exporter could not finish polling the Auth0 user client to fetch the tenant users."+
 				"Please increase the prometheus scrape period ", "users_found", len(eventUsers))
+			e.state.RecordBadEvent()
 		case errors.Is(err, context.DeadlineExceeded):
 			eventUsers := list.([]*management.User)
 			e.logger.V(0).Error(err, "Request could not be completed in the current request timeout. The exporter could not finish polling the Auth0 user client to fetch the tenant users."+

pkg/exporter/server.go

@@ -75,6 +75,10 @@ func (e *exporter) Export() error {
 			</html>`, e.metricsAddr))
 	})
 	server.GET("/healthz", func(ctx echo.Context) error {
+		// check if the exporter might be stuck
+		if e.state.IsBadState() {
+			return echo.ErrInternalServerError
+		}
 		return ctx.JSON(http.StatusOK, "ok")
 	})
 
@@ -112,6 +116,9 @@ func (e *exporter) Export() error {
 			return server.Start(fmt.Sprintf(":%d", e.hostPort))
 		})
 	}
+	grp.Go(func() error {
+		return e.state.Start(ctx)
+	})
 	grp.Go(func() error {
 		<-ctx.Done()
 		return server.Shutdown(context.Background())