type Balancer interface {
	// Balancer is called on specified client connection. Client initiates gRPC
	// connection with "grpc.Dial(addr, grpc.WithBalancerName)", and then those resolved
	// addresses are passed to "grpc/balancer.Balancer.HandleResolvedAddrs".
	// For each resolved address, balancer calls "balancer.ClientConn.NewSubConn".
	// "grpc/balancer.Balancer.HandleSubConnStateChange" is called when connectivity state
	// changes, thus requires failover logic in this method.
	balancer.Balancer

	// Picker calls "Pick" for every client request.
	picker.Picker
}

type Config struct {
	// Policy configures balancer policy.
	Policy picker.Policy

	// Name defines an additional name for balancer.
	// Useful for balancer testing to avoid register conflicts.
	// If empty, defaults to policy name.
	Name string

	// Logger configures balancer logging.
	// If nil, logs are discarded.
	Logger *zap.Logger
}