Fixed instancer logic for Consul (#1215)

The instancer loop was never updating the lastIndex but passing it to getInstances which caused Instancer to spam Consul repeatedly and nearly killed our Consul agent pods and time instances were added or removed from Consul for that service.

Author: jkratz55

sd/consul/instancer.go

@@ -65,9 +65,9 @@ func (s *Instancer) loop(lastIndex uint64) {
 		instances []string
 		err       error
 		d         time.Duration = 10 * time.Millisecond
+		index     uint64
 	)
 	for {
-		index := lastIndex
 		instances, index, err = s.getInstances(lastIndex, s.quitc)
 		switch {
 		case errors.Is(err, errStopped):
@@ -82,11 +82,12 @@ func (s *Instancer) loop(lastIndex uint64) {
 			time.Sleep(d)
 			d = conn.Exponential(d)
 		case index < lastIndex:
-			s.logger.Log("err", "index is less than previous; reseting to default")
+			s.logger.Log("err", "index is less than previous; resetting to default")
 			lastIndex = defaultIndex
 			time.Sleep(d)
 			d = conn.Exponential(d)
 		default:
+			lastIndex = index
 			s.cache.Update(sd.Event{Instances: instances})
 			d = 10 * time.Millisecond
 		}

sd/consul/instancer_test.go

@@ -2,6 +2,7 @@ package consul
 
 import (
 	"context"
+	"fmt"
 	"io"
 	"testing"
 	"time"
@@ -261,3 +262,66 @@ func TestInstancerWithInvalidIndex(t *testing.T) {
 		t.Error("failed, to receive call in time")
 	}
 }
+
+type indexTestClient struct {
+	client *testClient
+	index  uint64
+	errs   chan error
+}
+
+func newIndexTestClient(c *testClient, errs chan error) *indexTestClient {
+	return &indexTestClient{
+		client: c,
+		index:  0,
+		errs:   errs,
+	}
+}
+
+func (i *indexTestClient) Register(r *consul.AgentServiceRegistration) error {
+	return i.client.Register(r)
+}
+
+func (i *indexTestClient) Deregister(r *consul.AgentServiceRegistration) error {
+	return i.client.Deregister(r)
+}
+
+func (i *indexTestClient) Service(service, tag string, passingOnly bool, queryOpts *consul.QueryOptions) ([]*consul.ServiceEntry, *consul.QueryMeta, error) {
+
+	// Assumes this is the first call Service, loop hasn't begun running yet
+	if i.index == 0 && queryOpts.WaitIndex == 0 {
+		i.index = 100
+		entries, meta, err := i.client.Service(service, tag, passingOnly, queryOpts)
+		meta.LastIndex = i.index
+		return entries, meta, err
+	}
+
+	if queryOpts.WaitIndex < i.index {
+		i.errs <- fmt.Errorf("wait index %d is less than or equal to previous value", queryOpts.WaitIndex)
+	}
+
+	entries, meta, err := i.client.Service(service, tag, passingOnly, queryOpts)
+	i.index++
+	meta.LastIndex = i.index
+	return entries, meta, err
+}
+
+func TestInstancerLoopIndex(t *testing.T) {
+
+	var (
+		errs   = make(chan error, 1)
+		logger = log.NewNopLogger()
+		client = newIndexTestClient(newTestClient(consulState), errs)
+	)
+
+	go func() {
+		for err := range errs {
+			t.Error(err)
+			t.FailNow()
+		}
+	}()
+
+	instancer := NewInstancer(client, logger, "search", []string{"api"}, true)
+	defer instancer.Stop()
+
+	time.Sleep(2 * time.Second)
+}