code: func (a *Agent) EnableNodeMaintenance(reason, token string) {
  	// Ensure node maintenance is not already enabled
  	if _, ok := a.State.Checks()[structs.NodeMaint]; ok {
  		return
  	}
  
  	// Use a default notes value
  	if reason == "" {
  		reason = defaultNodeMaintReason
  	}
  
  	// Create and register the node maintenance check
  	check := &structs.HealthCheck{
  		Node:    a.config.NodeName,
  		CheckID: structs.NodeMaint,
  		Name:    "Node Maintenance Mode",
  		Notes:   reason,
  		Status:  api.HealthCritical,
  	}
  	a.AddCheck(check, nil, true, token, ConfigSourceLocal)
  	a.logger.Printf("[INFO] agent: Node entered maintenance mode")
  }
docs: // EnableNodeMaintenance places a node into maintenance mode.