Avoid ListBuckets() call instead rely on simple HTTP GET (#8475)

This is to avoid making calls to backend and requiring
gateways to allow permissions for ListBuckets() operation
just for Liveness checks, we can avoid this and make
our liveness checks to be more performant.

cmd/gateway-common.go

@@ -17,8 +17,10 @@
 package cmd
 
 import (
+	"context"
 	"net/http"
 	"strings"
+	"time"
 
 	"github.com/minio/minio/cmd/config"
 	xhttp "github.com/minio/minio/cmd/http"
@@ -286,6 +288,28 @@ func ToMinioClientCompleteParts(parts []CompletePart) []minio.CompletePart {
 	return mparts
 }
 
+// IsBackendOnline - verifies if the backend is reachable
+// by performing a GET request on the URL. returns 'true'
+// if backend is reachable.
+func IsBackendOnline(ctx context.Context, clnt *http.Client, urlStr string) bool {
+	ctx, cancel := context.WithTimeout(ctx, 1*time.Second)
+	defer cancel()
+
+	// never follow redirects
+	clnt.CheckRedirect = func(*http.Request, []*http.Request) error {
+		return http.ErrUseLastResponse
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, urlStr, nil)
+	if err != nil {
+		return false
+	}
+	if _, err = clnt.Do(req); err != nil {
+		return !xnet.IsNetworkOrHostDown(err)
+	}
+	return true
+}
+
 // ErrorRespToObjectError converts MinIO errors to minio object layer errors.
 func ErrorRespToObjectError(err error, params ...string) error {
 	if err == nil {

cmd/gateway/azure/gateway-azure.go

@@ -185,6 +185,8 @@ func (g *Azure) NewGatewayLayer(creds auth.Credentials) (minio.ObjectLayer, erro
 	c.HTTPClient = &http.Client{Transport: minio.NewCustomHTTPTransport()}
 
 	return &azureObjects{
+		endpoint:   fmt.Sprintf("https://%s.blob.core.windows.net", creds.AccessKey),
+		httpClient: c.HTTPClient,
 		client:     c.GetBlobService(),
 	}, nil
 }
@@ -343,6 +345,8 @@ func azurePropertiesToS3Meta(meta storage.BlobMetadata, props storage.BlobProper
 // azureObjects - Implements Object layer for Azure blob storage.
 type azureObjects struct {
 	minio.GatewayUnsupported
+	endpoint   string
+	httpClient *http.Client
 	client     storage.BlobStorageClient // Azure sdk client
 }
 
@@ -447,6 +451,8 @@ func (a *azureObjects) Shutdown(ctx context.Context) error {
 
 // StorageInfo - Not relevant to Azure backend.
 func (a *azureObjects) StorageInfo(ctx context.Context) (si minio.StorageInfo) {
+	si.Backend.Type = minio.BackendGateway
+	si.Backend.GatewayOnline = minio.IsBackendOnline(ctx, a.httpClient, a.endpoint)
 	return si
 }
 

cmd/gateway/b2/gateway-b2.go

@@ -123,6 +123,9 @@ func (g *B2) NewGatewayLayer(creds auth.Credentials) (minio.ObjectLayer, error)
 	return &b2Objects{
 		creds:    creds,
 		b2Client: client,
+		httpClient: &http.Client{
+			Transport: minio.NewCustomHTTPTransport(),
+		},
 		ctx: ctx,
 	}, nil
 }
@@ -138,6 +141,7 @@ type b2Objects struct {
 	mu         sync.Mutex
 	creds      auth.Credentials
 	b2Client   *b2.B2
+	httpClient *http.Client
 	ctx        context.Context
 }
 
@@ -225,12 +229,13 @@ func b2MsgCodeToObjectError(code int, msgCode string, msg string, params ...stri
 // Shutdown saves any gateway metadata to disk
 // if necessary and reload upon next restart.
 func (l *b2Objects) Shutdown(ctx context.Context) error {
-	// TODO
 	return nil
 }
 
 // StorageInfo is not relevant to B2 backend.
 func (l *b2Objects) StorageInfo(ctx context.Context) (si minio.StorageInfo) {
+	si.Backend.Type = minio.BackendGateway
+	si.Backend.GatewayOnline = minio.IsBackendOnline(ctx, l.httpClient, "https://api.backblazeb2.com/b2api/v1")
 	return si
 }
 

cmd/gateway/gcs/gateway-gcs.go

@@ -208,6 +208,9 @@ func (g *GCS) NewGatewayLayer(creds auth.Credentials) (minio.ObjectLayer, error)
 	gcs := &gcsGateway{
 		client:    client,
 		projectID: g.projectID,
+		httpClient: &http.Client{
+			Transport: minio.NewCustomHTTPTransport(),
+		},
 	}
 
 	// Start background process to cleanup old files in minio.sys.tmp
@@ -347,6 +350,7 @@ func isValidGCSProjectIDFormat(projectID string) bool {
 type gcsGateway struct {
 	minio.GatewayUnsupported
 	client     *storage.Client
+	httpClient *http.Client
 	projectID  string
 }
 
@@ -412,8 +416,10 @@ func (l *gcsGateway) Shutdown(ctx context.Context) error {
 }
 
 // StorageInfo - Not relevant to GCS backend.
-func (l *gcsGateway) StorageInfo(ctx context.Context) minio.StorageInfo {
-	return minio.StorageInfo{}
+func (l *gcsGateway) StorageInfo(ctx context.Context) (si minio.StorageInfo) {
+	si.Backend.Type = minio.BackendGateway
+	si.Backend.GatewayOnline = minio.IsBackendOnline(ctx, l.httpClient, "https://storage.googleapis.com")
+	return si
 }
 
 // MakeBucketWithLocation - Create a new container on GCS backend.

cmd/gateway/hdfs/gateway-hdfs.go

@@ -227,7 +227,8 @@ func (n *hdfsObjects) StorageInfo(ctx context.Context) minio.StorageInfo {
 	}
 	sinfo := minio.StorageInfo{}
 	sinfo.Used = []uint64{fsInfo.Used}
-	sinfo.Backend.Type = minio.Unknown
+	sinfo.Backend.Type = minio.BackendGateway
+	sinfo.Backend.GatewayOnline = true
 	return sinfo
 }
 

cmd/gateway/nas/gateway-nas.go

@@ -125,7 +125,8 @@ func (n *nasObjects) IsListenBucketSupported() bool {
 
 func (n *nasObjects) StorageInfo(ctx context.Context) minio.StorageInfo {
 	sinfo := n.ObjectLayer.StorageInfo(ctx)
-	sinfo.Backend.Type = minio.Unknown
+	sinfo.Backend.GatewayOnline = sinfo.Backend.Type == minio.BackendFS
+	sinfo.Backend.Type = minio.BackendGateway
 	return sinfo
 }
 

cmd/gateway/oss/gateway-oss.go

@@ -145,7 +145,9 @@ func (g *OSS) NewGatewayLayer(creds auth.Credentials) (minio.ObjectLayer, error)
 	if err != nil {
 		return nil, err
 	}
-
+	client.HTTPClient = &http.Client{
+		Transport: minio.NewCustomHTTPTransport(),
+	}
 	return &ossObjects{
 		Client: client,
 	}, nil
@@ -341,7 +343,9 @@ func (l *ossObjects) Shutdown(ctx context.Context) error {
 
 // StorageInfo is not relevant to OSS backend.
 func (l *ossObjects) StorageInfo(ctx context.Context) (si minio.StorageInfo) {
-	return
+	si.Backend.Type = minio.BackendGateway
+	si.Backend.GatewayOnline = minio.IsBackendOnline(ctx, l.Client.HTTPClient, l.Client.Config.Endpoint)
+	return si
 }
 
 // ossIsValidBucketName verifies whether a bucket name is valid.

cmd/gateway/s3/gateway-s3.go

@@ -261,7 +261,11 @@ func (g *S3) NewGatewayLayer(creds auth.Credentials) (minio.ObjectLayer, error)
 
 	s := s3Objects{
 		Client: clnt,
+		HTTPClient: &http.Client{
+			Transport: minio.NewCustomHTTPTransport(),
+		},
 	}
+
 	// Enables single encryption of KMS is configured.
 	if minio.GlobalKMS != nil {
 		encS := s3EncObjects{s}
@@ -284,6 +288,7 @@ func (g *S3) Production() bool {
 type s3Objects struct {
 	minio.GatewayUnsupported
 	Client     *miniogo.Core
+	HTTPClient *http.Client
 }
 
 // Shutdown saves any gateway metadata to disk
@@ -294,6 +299,8 @@ func (l *s3Objects) Shutdown(ctx context.Context) error {
 
 // StorageInfo is not relevant to S3 backend.
 func (l *s3Objects) StorageInfo(ctx context.Context) (si minio.StorageInfo) {
+	si.Backend.Type = minio.BackendGateway
+	si.Backend.GatewayOnline = minio.IsBackendOnline(ctx, l.HTTPClient, l.Client.EndpointURL().String())
 	return si
 }
 

cmd/healthcheck-handler.go

@@ -59,18 +59,15 @@ func LivenessCheckHandler(w http.ResponseWriter, r *http.Request) {
 		// is able to start on orchestration platforms like Docker Swarm.
 		// Refer https://github.com/minio/minio/issues/8140 for more details.
 		// Make sure to add server not initialized status in header
-		w.Header().Set(xhttp.MinIOServerStatus, "Server-not-initialized")
+		w.Header().Set(xhttp.MinIOServerStatus, "server-not-initialized")
 		writeSuccessResponseHeadersOnly(w)
 		return
 	}
 
 	if !globalIsXL && !globalIsDistXL {
 		s := objLayer.StorageInfo(ctx)
-		// Gateways don't provide disk info.
-		if s.Backend.Type == Unknown {
-			// ListBuckets to confirm gateway backend is up
-			if _, err := objLayer.ListBuckets(ctx); err != nil {
-				logger.LogOnceIf(ctx, err, struct{}{})
+		if s.Backend.Type == BackendGateway {
+			if !s.Backend.GatewayOnline {
 				writeResponse(w, http.StatusServiceUnavailable, nil, mimeNone)
 				return
 			}

cmd/object-api-datatypes.go

@@ -34,6 +34,8 @@ const (
 	BackendFS
 	// Multi disk BackendErasure (single, distributed) backend.
 	BackendErasure
+	// Gateway backend.
+	BackendGateway
 	// Add your own backend.
 )
 
@@ -49,9 +51,12 @@ type StorageInfo struct {
 
 	// Backend type.
 	Backend struct {
-		// Represents various backend types, currently on FS and Erasure.
+		// Represents various backend types, currently on FS, Erasure and Gateway
 		Type BackendType
 
+		// Following fields are only meaningful if BackendType is Gateway.
+		GatewayOnline bool
+
 		// Following fields are only meaningful if BackendType is Erasure.
 		OnlineDisks      madmin.BackendDisks // Online disks during server startup.
 		OfflineDisks     madmin.BackendDisks // Offline disks during server startup.