type Balancer interface {
	// Next returns next connection for request.
	// Next MUST not return nil if it has at least one connection.
	Next() conn.Conn

	// Insert inserts new connection.
	Insert(conn.Conn) Element

	// Update updates previously inserted connection.
	Update(Element, info.Info)

	// Remove removes previously inserted connection.
	Remove(Element)

	// Contains returns true if Balancer contains requested element.
	Contains(Element) bool
}

type Element interface{}