From 89d58bec1652794793682f4d97b01fe663448b6a Mon Sep 17 00:00:00 2001
From: Harshavardhana <harsha@minio.io>
Date: Thu, 8 Apr 2021 17:51:59 -0700
Subject: [PATCH] avoid frequent DNS lookups for baremetal setups (#11972)

bump up the DNS cache for baremetal setups upto 10 minutes
---
 cmd/common-main.go        | 10 +++++++++-
 cmd/http/dial_dnscache.go |  7 ++++++-
 cmd/update.go             | 13 ++++++++++---
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/cmd/common-main.go b/cmd/common-main.go
index 0550f6a5e..4b55a3685 100644
--- a/cmd/common-main.go
+++ b/cmd/common-main.go
@@ -59,7 +59,15 @@ func init() {
 	config.Logger.Info = logger.Info
 	config.Logger.LogIf = logger.LogIf
 
-	globalDNSCache = xhttp.NewDNSCache(10*time.Second, 10*time.Second, logger.LogOnceIf)
+	if IsKubernetes() || IsDocker() || IsBOSH() || IsDCOS() || IsKubernetesReplicaSet() || IsPCFTile() {
+		// 30 seconds matches the orchestrator DNS TTLs, have
+		// a 5 second timeout to lookup from DNS servers.
+		globalDNSCache = xhttp.NewDNSCache(30*time.Second, 5*time.Second, logger.LogOnceIf)
+	} else {
+		// On bare-metals DNS do not change often, so it is
+		// safe to assume a higher timeout upto 10 minutes.
+		globalDNSCache = xhttp.NewDNSCache(10*time.Minute, 5*time.Second, logger.LogOnceIf)
+	}
 
 	initGlobalContext()
 
diff --git a/cmd/http/dial_dnscache.go b/cmd/http/dial_dnscache.go
index bbfaabdb1..5513597be 100644
--- a/cmd/http/dial_dnscache.go
+++ b/cmd/http/dial_dnscache.go
@@ -121,6 +121,8 @@ func NewDNSCache(freq time.Duration, lookupTimeout time.Duration, loggerOnce fun
 		doneCh:        make(chan struct{}),
 	}
 
+	rnd := rand.New(rand.NewSource(time.Now().UnixNano()))
+
 	timer := time.NewTimer(freq)
 	go func() {
 		defer timer.Stop()
@@ -128,7 +130,10 @@ func NewDNSCache(freq time.Duration, lookupTimeout time.Duration, loggerOnce fun
 		for {
 			select {
 			case <-timer.C:
-				timer.Reset(freq)
+				// Make sure that refreshes on DNS do not be attempted
+				// at the same time, allows for reduced load on the
+				// DNS servers.
+				timer.Reset(time.Duration(rnd.Float64() * float64(freq)))
 
 				r.Refresh()
 			case <-r.doneCh:
diff --git a/cmd/update.go b/cmd/update.go
index f9fe982de..e98f1c523 100644
--- a/cmd/update.go
+++ b/cmd/update.go
@@ -221,6 +221,11 @@ func IsSourceBuild() bool {
 	return err != nil
 }
 
+// IsPCFTile returns if server is running in PCF
+func IsPCFTile() bool {
+	return env.Get("MINIO_PCF_TILE_VERSION", "") != ""
+}
+
 // DO NOT CHANGE USER AGENT STYLE.
 // The style should be
 //
@@ -286,9 +291,11 @@ func getUserAgent(mode string) string {
 		}
 	}
 
-	pcfTileVersion := env.Get("MINIO_PCF_TILE_VERSION", "")
-	if pcfTileVersion != "" {
-		uaAppend(" MinIO/pcf-tile-", pcfTileVersion)
+	if IsPCFTile() {
+		pcfTileVersion := env.Get("MINIO_PCF_TILE_VERSION", "")
+		if pcfTileVersion != "" {
+			uaAppend(" MinIO/pcf-tile-", pcfTileVersion)
+		}
 	}
 
 	return strings.Join(userAgentParts, "")