[release-19.0] prevent vtctld from creating tons of S3 connections (#15296)

go/vt/mysqlctl/s3backupstorage/s3.go

@@ -281,10 +281,21 @@
 
 // S3BackupStorage implements the backupstorage.BackupStorage interface.
 type S3BackupStorage struct {
-	_client *s3.S3
-	mu      sync.Mutex
-	s3SSE   S3ServerSideEncryption
-	params  backupstorage.Params
+	_client   *s3.S3
+	mu        sync.Mutex
+	s3SSE     S3ServerSideEncryption
+	params    backupstorage.Params
+	transport *http.Transport
+}
+
+func newS3BackupStorage() *S3BackupStorage {
+	// This initialises a new transport based off http.DefaultTransport the first time and returns the same
+	// transport on subsequent calls so connections can be reused as part of the same transport.
+	tlsClientConf := &tls.Config{InsecureSkipVerify: tlsSkipVerifyCert}
+	transport := http.DefaultTransport.(*http.Transport).Clone()
+	transport.TLSClientConfig = tlsClientConf
+
+	return &S3BackupStorage{params: backupstorage.NoParams(), transport: transport}
 }
 
 // ListBackups is part of the backupstorage.BackupStorage interface.
@@ -445,9 +456,7 @@
 	if bs._client == nil {
 		logLevel := getLogLevel()
 
-		tlsClientConf := &tls.Config{InsecureSkipVerify: tlsSkipVerifyCert}
-		httpTransport := &http.Transport{TLSClientConfig: tlsClientConf}
-		httpClient := &http.Client{Transport: httpTransport}
+		httpClient := &http.Client{Transport: bs.transport}
 
 		session, err := session.NewSession()
 		if err != nil {
@@ -497,7 +506,7 @@
 }
 
 func init() {
-	backupstorage.BackupStorageMap["s3"] = &S3BackupStorage{params: backupstorage.NoParams()}
+	backupstorage.BackupStorageMap["s3"] = newS3BackupStorage()
 
 	logNameMap = logNameToLogLevel{
 		"LogOff":                     aws.LogOff,

go/vt/mysqlctl/s3backupstorage/s3_test.go

@@ -276,3 +276,13 @@ func TestSSECustomerFileBase64Key(t *testing.T) {
 	assert.Nil(t, sseData.customerKey, "customerKey expected to be nil")
 	assert.Nil(t, sseData.customerMd5, "customerMd5 expected to be nil")
 }
+
+func TestNewS3Transport(t *testing.T) {
+	s3 := newS3BackupStorage()
+
+	// checking some of the values are present in the returned transport and match the http.DefaultTransport.
+	assert.Equal(t, http.DefaultTransport.(*http.Transport).IdleConnTimeout, s3.transport.IdleConnTimeout)
+	assert.Equal(t, http.DefaultTransport.(*http.Transport).MaxIdleConns, s3.transport.MaxIdleConns)
+	assert.NotNil(t, s3.transport.DialContext)
+	assert.NotNil(t, s3.transport.Proxy)
+}