Add healthchecker to check broker connection

healthcheck.go

@@ -0,0 +1,80 @@
+// Copyright 2020 Kentaro Hibino. All rights reserved.
+// Use of this source code is governed by a MIT license
+// that can be found in the LICENSE file.
+
+package asynq
+
+import (
+	"sync"
+	"time"
+
+	"github.com/hibiken/asynq/internal/base"
+	"github.com/hibiken/asynq/internal/log"
+)
+
+// healthchecker is responsible for pinging broker periodically
+// and call user provided HeathCheckFunc with the ping result.
+type healthchecker struct {
+	logger *log.Logger
+	broker base.Broker
+
+	// channel to communicate back to the long running "healthchecker" goroutine.
+	done chan struct{}
+
+	// interval between healthchecks.
+	interval time.Duration
+
+	// function to call periodically.
+	healthcheckFunc func(error)
+}
+
+type healthcheckerParams struct {
+	logger          *log.Logger
+	broker          base.Broker
+	interval        time.Duration
+	healthcheckFunc func(error)
+}
+
+func newHealthChecker(params healthcheckerParams) *healthchecker {
+	return &healthchecker{
+		logger:          params.logger,
+		broker:          params.broker,
+		done:            make(chan struct{}),
+		interval:        params.interval,
+		healthcheckFunc: params.healthcheckFunc,
+	}
+}
+
+func (hc *healthchecker) terminate() {
+	if hc.healthcheckFunc == nil {
+		return
+	}
+
+	hc.logger.Debug("Healthchecker shutting down...")
+	// Signal the healthchecker goroutine to stop.
+	hc.done <- struct{}{}
+}
+
+func (hc *healthchecker) start(wg *sync.WaitGroup) {
+	if hc.healthcheckFunc == nil {
+		return
+	}
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		timer := time.NewTimer(hc.interval)
+		for {
+			select {
+			case <-hc.done:
+				hc.logger.Debug("Healthchecker done")
+				timer.Stop()
+				return
+			case <-timer.C:
+				err := hc.broker.Ping()
+				hc.healthcheckFunc(err)
+				timer.Reset(hc.interval)
+			}
+		}
+	}()
+}

healthcheck_test.go

@@ -0,0 +1,101 @@
+// Copyright 2020 Kentaro Hibino. All rights reserved.
+// Use of this source code is governed by a MIT license
+// that can be found in the LICENSE file.
+
+package asynq
+
+import (
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/hibiken/asynq/internal/rdb"
+	"github.com/hibiken/asynq/internal/testbroker"
+)
+
+func TestHealthChecker(t *testing.T) {
+	r := setup(t)
+	rdbClient := rdb.NewRDB(r)
+
+	var (
+		// mu guards called and e variables.
+		mu     sync.Mutex
+		called int
+		e      error
+	)
+	checkFn := func(err error) {
+		mu.Lock()
+		defer mu.Unlock()
+		called++
+		e = err
+	}
+
+	hc := newHealthChecker(healthcheckerParams{
+		logger:          testLogger,
+		broker:          rdbClient,
+		interval:        1 * time.Second,
+		healthcheckFunc: checkFn,
+	})
+
+	hc.start(&sync.WaitGroup{})
+
+	time.Sleep(2 * time.Second)
+
+	mu.Lock()
+	if called == 0 {
+		t.Errorf("Healthchecker did not call the provided HealthCheckFunc")
+	}
+	if e != nil {
+		t.Errorf("HealthCheckFunc was called with non-nil error: %v", e)
+	}
+	mu.Unlock()
+
+	hc.terminate()
+}
+
+func TestHealthCheckerWhenRedisDown(t *testing.T) {
+	// Make sure that healthchecker goroutine doesn't panic
+	// if it cannot connect to redis.
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("panic occurred: %v", r)
+		}
+	}()
+	r := rdb.NewRDB(setup(t))
+	testBroker := testbroker.NewTestBroker(r)
+	var (
+		// mu guards called and e variables.
+		mu     sync.Mutex
+		called int
+		e      error
+	)
+	checkFn := func(err error) {
+		mu.Lock()
+		defer mu.Unlock()
+		called++
+		e = err
+	}
+
+	hc := newHealthChecker(healthcheckerParams{
+		logger:          testLogger,
+		broker:          testBroker,
+		interval:        1 * time.Second,
+		healthcheckFunc: checkFn,
+	})
+
+	testBroker.Sleep()
+	hc.start(&sync.WaitGroup{})
+
+	time.Sleep(2 * time.Second)
+
+	mu.Lock()
+	if called == 0 {
+		t.Errorf("Healthchecker did not call the provided HealthCheckFunc")
+	}
+	if e == nil {
+		t.Errorf("HealthCheckFunc was called with nil; want non-nil error")
+	}
+	mu.Unlock()
+
+	hc.terminate()
+}

internal/base/base.go

@@ -263,6 +263,7 @@ func (c *Cancelations) Get(id string) (fn context.CancelFunc, ok bool) {
 //
 // See rdb.RDB as a reference implementation.
 type Broker interface {
+	Ping() error
 	Enqueue(msg *TaskMessage) error
 	EnqueueUnique(msg *TaskMessage, ttl time.Duration) error
 	Dequeue(qnames ...string) (*TaskMessage, time.Time, error)

internal/rdb/rdb.go

@@ -45,6 +45,11 @@ func (r *RDB) Close() error {
 	return r.client.Close()
 }
 
+// Ping checks the connection with redis server.
+func (r *RDB) Ping() error {
+	return r.client.Ping().Err()
+}
+
 // KEYS[1] -> asynq:queues:<qname>
 // KEYS[2] -> asynq:queues
 // ARGV[1] -> task message data

internal/testbroker/testbroker.go

@@ -180,6 +180,15 @@ func (tb *TestBroker) PublishCancelation(id string) error {
 	return tb.real.PublishCancelation(id)
 }
 
+func (tb *TestBroker) Ping() error {
+	tb.mu.Lock()
+	defer tb.mu.Unlock()
+	if tb.sleeping {
+		return errRedisDown
+	}
+	return tb.real.Ping()
+}
+
 func (tb *TestBroker) Close() error {
 	tb.mu.Lock()
 	defer tb.mu.Unlock()

server.go

@@ -40,13 +40,14 @@ type Server struct {
 	status *base.ServerStatus
 
 	// wait group to wait for all goroutines to finish.
-	wg          sync.WaitGroup
-	scheduler   *scheduler
-	processor   *processor
-	syncer      *syncer
-	heartbeater *heartbeater
-	subscriber  *subscriber
-	recoverer   *recoverer
+	wg            sync.WaitGroup
+	scheduler     *scheduler
+	processor     *processor
+	syncer        *syncer
+	heartbeater   *heartbeater
+	subscriber    *subscriber
+	recoverer     *recoverer
+	healthchecker *healthchecker
 }
 
 // Config specifies the server's background-task processing behavior.
@@ -123,6 +124,15 @@ type Config struct {
 	//
 	// If unset or zero, default timeout of 8 seconds is used.
 	ShutdownTimeout time.Duration
+
+	// HealthCheckFunc is called periodically with any errors encountered during ping to the
+	// connected redis server.
+	HealthCheckFunc func(error)
+
+	// HealthCheckInterval specifies the interval between healthchecks.
+	//
+	// If unset or zero, the interval is set to 15 seconds.
+	HealthCheckInterval time.Duration
 }
 
 // An ErrorHandler handles an error occured during task processing.
@@ -250,7 +260,11 @@ var defaultQueueConfig = map[string]int{
 	base.DefaultQueueName: 1,
 }
 
-const defaultShutdownTimeout = 8 * time.Second
+const (
+	defaultShutdownTimeout = 8 * time.Second
+
+	defaultHealthCheckInterval = 15 * time.Second
+)
 
 // NewServer returns a new Server given a redis connection option
 // and background processing configuration.
@@ -276,6 +290,10 @@ func NewServer(r RedisConnOpt, cfg Config) *Server {
 	if shutdownTimeout == 0 {
 		shutdownTimeout = defaultShutdownTimeout
 	}
+	healthcheckInterval := cfg.HealthCheckInterval
+	if healthcheckInterval == 0 {
+		healthcheckInterval = defaultHealthCheckInterval
+	}
 	logger := log.NewLogger(cfg.Logger)
 	loglevel := cfg.LogLevel
 	if loglevel == level_unspecified {
@@ -336,16 +354,23 @@ func NewServer(r RedisConnOpt, cfg Config) *Server {
 		retryDelayFunc: delayFunc,
 		interval:       1 * time.Minute,
 	})
+	healthchecker := newHealthChecker(healthcheckerParams{
+		logger:          logger,
+		broker:          rdb,
+		interval:        healthcheckInterval,
+		healthcheckFunc: cfg.HealthCheckFunc,
+	})
 	return &Server{
-		logger:      logger,
-		broker:      rdb,
-		status:      status,
-		scheduler:   scheduler,
-		processor:   processor,
-		syncer:      syncer,
-		heartbeater: heartbeater,
-		subscriber:  subscriber,
-		recoverer:   recoverer,
+		logger:        logger,
+		broker:        rdb,
+		status:        status,
+		scheduler:     scheduler,
+		processor:     processor,
+		syncer:        syncer,
+		heartbeater:   heartbeater,
+		subscriber:    subscriber,
+		recoverer:     recoverer,
+		healthchecker: healthchecker,
 	}
 }
 
@@ -413,6 +438,7 @@ func (srv *Server) Start(handler Handler) error {
 	srv.logger.Info("Starting processing")
 
 	srv.heartbeater.start(&srv.wg)
+	srv.healthchecker.start(&srv.wg)
 	srv.subscriber.start(&srv.wg)
 	srv.syncer.start(&srv.wg)
 	srv.recoverer.start(&srv.wg)
@@ -442,6 +468,7 @@ func (srv *Server) Stop() {
 	srv.recoverer.terminate()
 	srv.syncer.terminate()
 	srv.subscriber.terminate()
+	srv.healthchecker.terminate()
 	srv.heartbeater.terminate()
 
 	srv.wg.Wait()