clientv3/balancer/balancer.go
func RegisterBuilder(cfg Config) {
	bb := &builder{cfg}
	balancer.Register(bb)

	bb.cfg.Logger.Debug(
		"registered balancer",
		zap.String("policy", bb.cfg.Policy.String()),
		zap.String("name", bb.cfg.Name),
	)
}
func RegisterBuilder(cfg Config) {
	bb := &builder{cfg}
	balancer.Register(bb)

	bb.cfg.Logger.Debug(
		"registered balancer",
		zap.String("policy", bb.cfg.Policy.String()),
		zap.String("name", bb.cfg.Name),
	)
}
// RegisterBuilder creates and registers a builder. Since this function calls balancer.Register, it
// must be invoked at initialization time.