type Config struct {
	// Policy specifies etcd clientv3's built in balancer policy.
	Policy Policy

	// Logger defines picker logging object.
	Logger *zap.Logger

	// SubConnToResolverAddress maps each gRPC sub-connection to an address.
	// Basically, it is a list of addresses that the Picker can pick from.
	SubConnToResolverAddress map[balancer.SubConn]resolver.Address
}

type Picker interface {
	balancer.Picker
	String() string
}

type Policy uint8

const (
	// Error is error picker policy.
	Error Policy = iota

	// RoundrobinBalanced balances loads over multiple endpoints
	// and implements failover in roundrobin fashion.
	RoundrobinBalanced

	// Custom defines custom balancer picker.
	// TODO: custom picker is not supported yet.
	Custom
)