fix: backend not reachable should be more descriptive (#13634)

cmd/api-errors.go

@@ -1362,8 +1362,8 @@ var errorCodes = errorCodeMap{
 	},
 	ErrBackendDown: {
 		Code:           "XMinioBackendDown",
-		Description:    "Object storage backend is unreachable",
+		Description:    "Remote backend is unreachable",
-		HTTPStatusCode: http.StatusServiceUnavailable,
+		HTTPStatusCode: http.StatusBadRequest,
 	},
 	ErrIncorrectContinuationToken: {
 		Code:           "InvalidArgument",
@@ -2129,6 +2129,11 @@ func toAPIError(ctx context.Context, err error) APIError {
 		}
 	}
 
+	if apiErr.Code == "XMinioBackendDown" {
+		apiErr.Description = fmt.Sprintf("%s (%v)", apiErr.Description, err)
+		return apiErr
+	}
+
 	if apiErr.Code == "InternalError" {
 		// If we see an internal error try to interpret
 		// any underlying errors if possible depending on

cmd/gateway-common.go

@@ -287,7 +287,7 @@ func ErrorRespToObjectError(err error, params ...string) error {
 	}
 
 	if xnet.IsNetworkOrHostDown(err, false) {
-		return BackendDown{}
+		return BackendDown{Err: err.Error()}
 	}
 
 	minioErr, ok := err.(minio.ErrorResponse)

cmd/object-api-errors.go

@@ -645,10 +645,12 @@ func (e UnsupportedMetadata) Error() string {
 }
 
 // BackendDown is returned for network errors or if the gateway's backend is down.
-type BackendDown struct{}
+type BackendDown struct {
+	Err string
+}
 
 func (e BackendDown) Error() string {
-	return "Backend down"
+	return e.Err
 }
 
 // isErrBucketNotFound - Check if error type is BucketNotFound.

cmd/warm-backend.go

@@ -50,6 +50,10 @@ func checkWarmBackend(ctx context.Context, w WarmBackend) error {
 	var empty bytes.Reader
 	rv, err := w.Put(ctx, probeObject, &empty, 0)
 	if err != nil {
+		switch err.(type) {
+		case BackendDown:
+			return err
+		}
 		return tierPermErr{
 			Op:  tierPut,
 			Err: err,
@@ -58,6 +62,10 @@ func checkWarmBackend(ctx context.Context, w WarmBackend) error {
 
 	_, err = w.Get(ctx, probeObject, rv, WarmBackendGetOpts{})
 	if err != nil {
+		switch err.(type) {
+		case BackendDown:
+			return err
+		}
 		switch {
 		case isErrBucketNotFound(err):
 			return errTierBucketNotFound
@@ -72,6 +80,10 @@ func checkWarmBackend(ctx context.Context, w WarmBackend) error {
 	}
 
 	if err = w.Remove(ctx, probeObject, rv); err != nil {
+		switch err.(type) {
+		case BackendDown:
+			return err
+		}
 		return tierPermErr{
 			Op:  tierDelete,
 			Err: err,