code: func (proxy *ProxyClient) FindServersByLabels(ctx context.Context, namespace string, labels map[string]string) ([]services.Server, error) {
  	if namespace == "" {
  		return nil, trace.BadParameter(auth.MissingNamespaceError)
  	}
  	nodes := make([]services.Server, 0)
  	site, err := proxy.CurrentClusterAccessPoint(ctx, false)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  
  	siteNodes, err := site.GetNodes(namespace, services.SkipValidation())
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  
  	// look at every node on this site and see which ones match:
  	for _, node := range siteNodes {
  		if node.MatchAgainst(labels) {
  			nodes = append(nodes, node)
  		}
  	}
  	return nodes, nil
  }
docs: // FindServersByLabels returns list of the nodes which have labels exactly matching
  // the given label set.
  //
  // A server is matched when ALL labels match.
  // If no labels are passed, ALL nodes are returned.