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/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
 			}