From 5479063f4eef127383c16cdc4073b85a6e7c40d9 Mon Sep 17 00:00:00 2001
From: Umputun <umputun@gmail.com>
Date: Tue, 13 Apr 2021 12:34:34 -0500
Subject: [PATCH] limit health check concurrency

---
 app/discovery/discovery_test.go |  2 +-
 app/proxy/health.go             | 11 +++++++++--
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/app/discovery/discovery_test.go b/app/discovery/discovery_test.go
index 08d10d2..8bb7032 100644
--- a/app/discovery/discovery_test.go
+++ b/app/discovery/discovery_test.go
@@ -11,7 +11,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestService_Do(t *testing.T) {
+func TestService_Run(t *testing.T) {
 	p1 := &ProviderMock{
 		EventsFunc: func(ctx context.Context) <-chan ProviderID {
 			res := make(chan ProviderID, 1)
diff --git a/app/proxy/health.go b/app/proxy/health.go
index 0c81fc3..16e1c09 100644
--- a/app/proxy/health.go
+++ b/app/proxy/health.go
@@ -27,18 +27,25 @@ func (h *Http) healthMiddleware(next http.Handler) http.Handler {
 
 func (h *Http) healthHandler(w http.ResponseWriter, _ *http.Request) {
 
+	const concurrent = 8
+	sema := make(chan struct{}, concurrent) // limit health check to 8 concurrent calls
+
 	// runs pings in parallel
 	check := func(mappers []discovery.URLMapper) (ok bool, valid int, total int, errs []string) {
-		outCh := make(chan error, 8)
+		outCh := make(chan error, concurrent)
 		var pinged int32
 		var wg sync.WaitGroup
 		for _, m := range mappers {
 			if m.PingURL == "" {
 				continue
 			}
+			sema <- struct{}{}
 			wg.Add(1)
 			go func(m discovery.URLMapper) {
-				defer wg.Done()
+				defer func() {
+					<-sema
+					wg.Done()
+				}()
 
 				atomic.AddInt32(&pinged, 1)
 				client := http.Client{Timeout: 100 * time.Millisecond}