From fddf4918c0b48a5a0e8916b9de108293f7069a42 Mon Sep 17 00:00:00 2001
From: Nick Triller <nicktriller@gmail.com>
Date: Wed, 28 Apr 2021 17:00:07 +0200
Subject: [PATCH] Send empty targetgroup if nothing discovered

Signed-off-by: Nick Triller <nicktriller@gmail.com>
---
 discovery/consul/consul.go      |  9 +++++++++
 discovery/consul/consul_test.go | 17 +++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/discovery/consul/consul.go b/discovery/consul/consul.go
index ee2734def..fa3d32303 100644
--- a/discovery/consul/consul.go
+++ b/discovery/consul/consul.go
@@ -426,6 +426,15 @@ func (d *Discovery) watchServices(ctx context.Context, ch chan<- []*targetgroup.
 			}
 		}
 	}
+
+	// Send targetgroup with no targets if nothing was discovered.
+	if len(services) == 0 {
+		select {
+		case <-ctx.Done():
+			return
+		case ch <- []*targetgroup.Group{{}}:
+		}
+	}
 }
 
 // consulService contains data belonging to the same service.
diff --git a/discovery/consul/consul_test.go b/discovery/consul/consul_test.go
index 0a6b73518..afc387c0b 100644
--- a/discovery/consul/consul_test.go
+++ b/discovery/consul/consul_test.go
@@ -298,6 +298,23 @@ func TestAllServices(t *testing.T) {
 	<-ch
 }
 
+// targetgroup with no targets is emitted if no services were discovered.
+func TestNoTargets(t *testing.T) {
+	stub, config := newServer(t)
+	defer stub.Close()
+	config.ServiceTags = []string{"missing"}
+
+	d := newDiscovery(t, config)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	ch := make(chan []*targetgroup.Group)
+	go d.Run(ctx, ch)
+
+	targets := (<-ch)[0].Targets
+	require.Equal(t, 0, len(targets))
+	cancel()
+}
+
 // Watch only the test service.
 func TestOneService(t *testing.T) {
 	stub, config := newServer(t)