code: func NewManager(configs map[string]*config.Service, defaultRoundTripper http.RoundTripper) *Manager {
  	return &Manager{
  		bufferPool:          newBufferPool(),
  		defaultRoundTripper: defaultRoundTripper,
  		balancers:           make(map[string][]healthcheck.BalancerHandler),
  		configs:             configs,
  	}
  }
docs: // NewManager creates a new Manager