code: func (n *Manager) Alertmanagers() []*url.URL {
  	n.mtx.RLock()
  	amSets := n.alertmanagers
  	n.mtx.RUnlock()
  
  	var res []*url.URL
  
  	for _, ams := range amSets {
  		ams.mtx.RLock()
  		for _, am := range ams.ams {
  			res = append(res, am.url())
  		}
  		ams.mtx.RUnlock()
  	}
  
  	return res
  }
docs: // Alertmanagers returns a slice of Alertmanager URLs.