code: func (g *Cloud) ensureInternalBackendServiceGroups(name string, igLinks []string) error {
  	klog.V(2).Infof("ensureInternalBackendServiceGroups(%v): checking existing backend service's groups", name)
  	bs, err := g.GetRegionBackendService(name, g.region)
  	if err != nil {
  		return err
  	}
  
  	backends := backendsFromGroupLinks(igLinks)
  	if backendsListEqual(bs.Backends, backends) {
  		return nil
  	}
  
  	// Set the backend service's backends to the updated list.
  	bs.Backends = backends
  
  	klog.V(2).Infof("ensureInternalBackendServiceGroups: updating backend service %v", name)
  	if err := g.UpdateRegionBackendService(bs, g.region); err != nil {
  		return err
  	}
  	klog.V(2).Infof("ensureInternalBackendServiceGroups: updated backend service %v successfully", name)
  	return nil
  }
docs: // ensureInternalBackendServiceGroups updates backend services if their list of backend instance groups is incorrect.