From 3c679293587ab2845b234cc3f0271e8e58203176 Mon Sep 17 00:00:00 2001
From: Bart Smykla <bsmykla@vmware.com>
Date: Mon, 14 Jan 2019 15:43:20 +0000
Subject: [PATCH] Added reconnection logic when NATS is disconnected

How was it tested:
I deployed this version of nats-queue-worker and then simulated
NATS disconnection

Signed-off-by: Bart Smykla <bsmykla@vmware.com>
---
 handler/handler.go     | 70 +++++++++++++++++++++++++++++++++++-------
 handler/nats_config.go | 20 ++++++++++++
 2 files changed, 79 insertions(+), 11 deletions(-)

diff --git a/handler/handler.go b/handler/handler.go
index 5eef9d5..c7e1f06 100644
--- a/handler/handler.go
+++ b/handler/handler.go
@@ -4,6 +4,8 @@ import (
 	"encoding/json"
 	"fmt"
 	"log"
+	"sync"
+	"time"
 
 	"github.com/nats-io/go-nats-streaming"
 	"github.com/openfaas/faas/gateway/queue"
@@ -11,13 +13,56 @@ import (
 
 // NatsQueue queue for work
 type NatsQueue struct {
-	nc        stan.Conn
+	nc             stan.Conn
+	ncMutex        *sync.RWMutex
+	maxReconnect   int
+	reconnectDelay time.Duration
+
 	ClientID  string
 	ClusterID string
 	NATSURL   string
 	Topic     string
 }
 
+func (q *NatsQueue) connect() error {
+	nc, err := stan.Connect(
+		q.ClusterID,
+		q.ClientID,
+		stan.NatsURL(q.NATSURL),
+		stan.SetConnectionLostHandler(func(conn stan.Conn, err error) {
+			log.Printf("Disconnected from %s\n", q.NATSURL)
+
+			q.reconnect()
+		}),
+	)
+
+	if err != nil {
+		return err
+	}
+
+	q.ncMutex.Lock()
+	q.nc = nc
+	q.ncMutex.Unlock()
+
+	return nil
+}
+
+func (q *NatsQueue) reconnect() {
+	for i := 0; i < q.maxReconnect; i++ {
+		time.Sleep(time.Second * time.Duration(i) * q.reconnectDelay)
+
+		if err := q.connect(); err == nil {
+			log.Printf("Reconnection (%d/%d) to %s succeeded", i + 1, q.maxReconnect, q.NATSURL)
+
+			return
+		}
+
+		log.Printf("Reconnection (%d/%d) to %s failed", i + 1, q.maxReconnect, q.NATSURL)
+	}
+
+	log.Printf("Reconnection limit (%d) reached\n", q.maxReconnect)
+}
+
 // CreateNatsQueue ready for asynchronous processing
 func CreateNatsQueue(address string, port int, clientConfig NatsConfig) (*NatsQueue, error) {
 	var err error
@@ -27,22 +72,23 @@ func CreateNatsQueue(address string, port int, clientConfig NatsConfig) (*NatsQu
 	clientID := clientConfig.GetClientID()
 	clusterID := "faas-cluster"
 
-	nc, err := stan.Connect(clusterID, clientID, stan.NatsURL(natsURL))
 	queue1 := NatsQueue{
-		nc:        nc,
-		ClientID:  clientID,
-		ClusterID: clusterID,
-		NATSURL:   natsURL,
-		Topic:     "faas-request",
+		ClientID:       clientID,
+		ClusterID:      clusterID,
+		NATSURL:        natsURL,
+		Topic:          "faas-request",
+		maxReconnect:   clientConfig.GetMaxReconnect(),
+		reconnectDelay: clientConfig.GetReconnectDelay(),
+		ncMutex:        &sync.RWMutex{},
 	}
 
+	err = queue1.connect()
+
 	return &queue1, err
 }
 
 // Queue request for processing
 func (q *NatsQueue) Queue(req *queue.Request) error {
-	var err error
-
 	fmt.Printf("NatsQueue - submitting request: %s.\n", req.Function)
 
 	out, err := json.Marshal(req)
@@ -50,7 +96,9 @@ func (q *NatsQueue) Queue(req *queue.Request) error {
 		log.Println(err)
 	}
 
-	err = q.nc.Publish(q.Topic, out)
+	q.ncMutex.RLock()
+	nc := q.nc
+	q.ncMutex.RUnlock()
 
-	return err
+	return nc.Publish(q.Topic, out)
 }
diff --git a/handler/nats_config.go b/handler/nats_config.go
index ca23329..1261a00 100644
--- a/handler/nats_config.go
+++ b/handler/nats_config.go
@@ -2,15 +2,27 @@ package handler
 
 import (
 	"os"
+	"time"
 
 	"github.com/openfaas/nats-queue-worker/nats"
 )
 
 type NatsConfig interface {
 	GetClientID() string
+	GetMaxReconnect() int
+	GetReconnectDelay() time.Duration
 }
 
 type DefaultNatsConfig struct {
+	maxReconnect          int
+	delayBetweenReconnect time.Duration
+}
+
+func NewDefaultNatsConfig() DefaultNatsConfig {
+	return DefaultNatsConfig{
+		maxReconnect: 5,
+		delayBetweenReconnect: time.Second * 2,
+	}
 }
 
 // GetClientID returns the ClientID assigned to this producer/consumer.
@@ -19,6 +31,14 @@ func (DefaultNatsConfig) GetClientID() string {
 	return getClientID(val)
 }
 
+func (c DefaultNatsConfig) GetMaxReconnect() int {
+	return c.maxReconnect
+}
+
+func (c DefaultNatsConfig) GetReconnectDelay() time.Duration {
+	return c.delayBetweenReconnect
+}
+
 func getClientID(hostname string) string {
 	return "faas-publisher-" + nats.GetClientID(hostname)
 }