Retry restarting receiver on PubSub service error (#5458)

plugins/inputs/cloud_pubsub/README.md

@@ -26,6 +26,12 @@ and creates metrics using one of the supported [input data formats][].
   ## Application Default Credentials, which is preferred.
   # credentials_file = "path/to/my/creds.json"
 
+  ## Optional. Number of seconds to wait before attempting to restart the 
+  ## PubSub subscription receiver after an unexpected error. 
+  ## If the streaming pull for a PubSub Subscription fails (receiver),
+  ## the agent attempts to restart receiving messages after this many seconds.
+  # retry_delay_seconds = 5
+  
   ## Optional. Maximum byte length of a message to consume.
   ## Larger messages are dropped with an error. If less than 0 or unspecified,
   ## treated as no limit.

plugins/inputs/cloud_pubsub/pubsub.go

@@ -12,14 +12,19 @@ import (
 	"github.com/influxdata/telegraf/plugins/parsers"
 	"golang.org/x/oauth2/google"
 	"google.golang.org/api/option"
+	"log"
+	"time"
 )
 
 type empty struct{}
 type semaphore chan empty
 
 const defaultMaxUndeliveredMessages = 1000
+const defaultRetryDelaySeconds = 5
 
 type PubSub struct {
+	sync.Mutex
+
 	CredentialsFile string `toml:"credentials_file"`
 	Project         string `toml:"project"`
 	Subscription    string `toml:"subscription"`
@@ -33,6 +38,7 @@ type PubSub struct {
 	// Agent settings
 	MaxMessageLen            int `toml:"max_message_len"`
 	MaxUndeliveredMessages   int `toml:"max_undelivered_messages"`
+	RetryReceiveDelaySeconds int `toml:"retry_delay_seconds"`
 
 	sub     subscription
 	stubSub func() subscription
@@ -42,7 +48,6 @@ type PubSub struct {
 	parser parsers.Parser
 	wg     *sync.WaitGroup
 	acc    telegraf.TrackingAccumulator
-	mu     sync.Mutex
 
 	undelivered map[telegraf.TrackingID]message
 	sem         semaphore
@@ -78,35 +83,36 @@ func (ps *PubSub) Start(ac telegraf.Accumulator) error {
 		return fmt.Errorf(`"project" is required`)
 	}
 
-	cctx, cancel := context.WithCancel(context.Background())
+	ps.sem = make(semaphore, ps.MaxUndeliveredMessages)
+	ps.acc = ac.WithTracking(ps.MaxUndeliveredMessages)
+
+	// Create top-level context with cancel that will be called on Stop().
+	ctx, cancel := context.WithCancel(context.Background())
 	ps.cancel = cancel
 
 	if ps.stubSub != nil {
 		ps.sub = ps.stubSub()
 	} else {
-		subRef, err := ps.getGCPSubscription(cctx, ps.Subscription)
+		subRef, err := ps.getGCPSubscription(ps.Subscription)
 		if err != nil {
-			return err
+			return fmt.Errorf("unable to create subscription handle: %v", err)
 		}
 		ps.sub = subRef
 	}
 
 	ps.wg = &sync.WaitGroup{}
-	ps.acc = ac.WithTracking(ps.MaxUndeliveredMessages)
-	ps.sem = make(semaphore, ps.MaxUndeliveredMessages)
-
-	// Start receiver in new goroutine for each subscription.
-	ps.wg.Add(1)
-	go func() {
-		defer ps.wg.Done()
-		ps.subReceive(cctx)
-	}()
-
 	// Start goroutine to handle delivery notifications from accumulator.
 	ps.wg.Add(1)
 	go func() {
 		defer ps.wg.Done()
-		ps.receiveDelivered(cctx)
+		ps.waitForDelivery(ctx)
+	}()
+
+	// Start goroutine for subscription receiver.
+	ps.wg.Add(1)
+	go func() {
+		defer ps.wg.Done()
+		ps.receiveWithRetry(ctx)
 	}()
 
 	return nil
@@ -119,13 +125,41 @@ func (ps *PubSub) Stop() {
 	ps.wg.Wait()
 }
 
-func (ps *PubSub) subReceive(cctx context.Context) {
+// startReceiver is called within a goroutine and manages keeping a
+// subscription.Receive() up and running while the plugin has not been stopped.
+func (ps *PubSub) receiveWithRetry(parentCtx context.Context) {
+	err := ps.startReceiver(parentCtx)
+
+	for err != nil && parentCtx.Err() == nil {
+		log.Printf("E! [inputs.cloud_pubsub] Receiver for subscription %s exited with error: %v", ps.sub.ID(), err)
+
+		delay := defaultRetryDelaySeconds
+		if ps.RetryReceiveDelaySeconds > 0 {
+			delay = ps.RetryReceiveDelaySeconds
+		}
+
+		log.Printf("I! [inputs.cloud_pubsub] Waiting %d seconds before attempting to restart receiver...", delay)
+		time.Sleep(time.Duration(delay) * time.Second)
+
+		err = ps.startReceiver(parentCtx)
+	}
+}
+
+func (ps *PubSub) startReceiver(parentCtx context.Context) error {
+	log.Printf("I! [inputs.cloud_pubsub] Starting receiver for subscription %s...", ps.sub.ID())
+	cctx, ccancel := context.WithCancel(parentCtx)
 	err := ps.sub.Receive(cctx, func(ctx context.Context, msg message) {
 		if err := ps.onMessage(ctx, msg); err != nil {
 			ps.acc.AddError(fmt.Errorf("unable to add message from subscription %s: %v", ps.sub.ID(), err))
 		}
 	})
+	if err != nil {
 		ps.acc.AddError(fmt.Errorf("receiver for subscription %s exited: %v", ps.sub.ID(), err))
+	} else {
+		log.Printf("I! [inputs.cloud_pubsub] subscription pull ended (no error, most likely stopped)")
+	}
+	ccancel()
+	return err
 }
 
 // onMessage handles parsing and adding a received message to the accumulator.
@@ -153,8 +187,8 @@ func (ps *PubSub) onMessage(ctx context.Context, msg message) error {
 		break
 	}
 
-	ps.mu.Lock()
-	defer ps.mu.Unlock()
+	ps.Lock()
+	defer ps.Unlock()
 
 	id := ps.acc.AddTrackingMetricGroup(metrics)
 	if ps.undelivered == nil {
@@ -165,10 +199,10 @@ func (ps *PubSub) onMessage(ctx context.Context, msg message) error {
 	return nil
 }
 
-func (ps *PubSub) receiveDelivered(ctx context.Context) {
+func (ps *PubSub) waitForDelivery(parentCtx context.Context) {
 	for {
 		select {
-		case <-ctx.Done():
+		case <-parentCtx.Done():
 			return
 		case info := <-ps.acc.Delivered():
 			<-ps.sem
@@ -182,8 +216,8 @@ func (ps *PubSub) receiveDelivered(ctx context.Context) {
 }
 
 func (ps *PubSub) removeDelivered(id telegraf.TrackingID) message {
-	ps.mu.Lock()
-	defer ps.mu.Unlock()
+	ps.Lock()
+	defer ps.Unlock()
 
 	msg, ok := ps.undelivered[id]
 	if !ok {
@@ -219,7 +253,7 @@ func (ps *PubSub) getPubSubClient() (*pubsub.Client, error) {
 	return client, nil
 }
 
-func (ps *PubSub) getGCPSubscription(ctx context.Context, subId string) (subscription, error) {
+func (ps *PubSub) getGCPSubscription(subId string) (subscription, error) {
 	client, err := ps.getPubSubClient()
 	if err != nil {
 		return nil, err
@@ -262,6 +296,12 @@ const sampleConfig = `
   ## Application Default Credentials, which is preferred.
   # credentials_file = "path/to/my/creds.json"
 
+  ## Optional. Number of seconds to wait before attempting to restart the 
+  ## PubSub subscription receiver after an unexpected error. 
+  ## If the streaming pull for a PubSub Subscription fails (receiver),
+  ## the agent attempts to restart receiving messages after this many seconds.
+  # retry_delay_seconds = 5
+
   ## Optional. Maximum byte length of a message to consume.
   ## Larger messages are dropped with an error. If less than 0 or unspecified,
   ## treated as no limit.

plugins/inputs/cloud_pubsub/pubsub_test.go

@@ -1,6 +1,7 @@
 package cloud_pubsub
 
 import (
+	"errors"
 	"github.com/influxdata/telegraf/plugins/parsers"
 	"github.com/influxdata/telegraf/testutil"
 	"github.com/stretchr/testify/assert"
@@ -21,6 +22,7 @@ func TestRunParse(t *testing.T) {
 		id:       subId,
 		messages: make(chan *testMsg, 100),
 	}
+	sub.receiver = testMessagesReceive(sub)
 
 	ps := &PubSub{
 		parser:                 testParser,
@@ -62,6 +64,7 @@ func TestRunInvalidMessages(t *testing.T) {
 		id:       subId,
 		messages: make(chan *testMsg, 100),
 	}
+	sub.receiver = testMessagesReceive(sub)
 
 	ps := &PubSub{
 		parser:                 testParser,
@@ -107,6 +110,7 @@ func TestRunOverlongMessages(t *testing.T) {
 		id:       subId,
 		messages: make(chan *testMsg, 100),
 	}
+	sub.receiver = testMessagesReceive(sub)
 
 	ps := &PubSub{
 		parser:                 testParser,
@@ -141,6 +145,41 @@ func TestRunOverlongMessages(t *testing.T) {
 	assert.Equal(t, acc.NFields(), 0)
 }
 
+func TestRunErrorInSubscriber(t *testing.T) {
+	subId := "sub-unexpected-error"
+
+	acc := &testutil.Accumulator{}
+
+	testParser, _ := parsers.NewInfluxParser()
+
+	sub := &stubSub{
+		id:       subId,
+		messages: make(chan *testMsg, 100),
+	}
+	fakeErrStr := "a fake error"
+	sub.receiver = testMessagesError(sub, errors.New("a fake error"))
+
+	ps := &PubSub{
+		parser:                   testParser,
+		stubSub:                  func() subscription { return sub },
+		Project:                  "projectIDontMatterForTests",
+		Subscription:             subId,
+		MaxUndeliveredMessages:   defaultMaxUndeliveredMessages,
+		RetryReceiveDelaySeconds: 1,
+	}
+
+	if err := ps.Start(acc); err != nil {
+		t.Fatalf("test PubSub failed to start: %s", err)
+	}
+	defer ps.Stop()
+
+	if ps.sub == nil {
+		t.Fatal("expected plugin subscription to be non-nil")
+	}
+	acc.WaitError(1)
+	assert.Regexp(t, fakeErrStr, acc.Errors[0])
+}
+
 func validateTestInfluxMetric(t *testing.T, m *testutil.Metric) {
 	assert.Equal(t, "cpu_load_short", m.Measurement)
 	assert.Equal(t, "server01", m.Tags["host"])

plugins/inputs/cloud_pubsub/subscription_stub.go

@@ -9,6 +9,7 @@ import (
 type stubSub struct {
 	id       string
 	messages chan *testMsg
+	receiver receiveFunc
 }
 
 func (s *stubSub) ID() string {
@@ -16,6 +17,19 @@ func (s *stubSub) ID() string {
 }
 
 func (s *stubSub) Receive(ctx context.Context, f func(context.Context, message)) error {
+	return s.receiver(ctx, f)
+}
+
+type receiveFunc func(ctx context.Context, f func(context.Context, message)) error
+
+func testMessagesError(s *stubSub, expectedErr error) receiveFunc {
+	return func(ctx context.Context, f func(context.Context, message)) error {
+		return expectedErr
+	}
+}
+
+func testMessagesReceive(s *stubSub) receiveFunc {
+	return func(ctx context.Context, f func(context.Context, message)) error {
 		for {
 			select {
 			case <-ctx.Done():
@@ -25,6 +39,7 @@ func (s *stubSub) Receive(ctx context.Context, f func(context.Context, message))
 			}
 		}
 	}
+}
 
 type testMsg struct {
 	id          string