type Agent interface {
	ID() uint64
	// Start starts a new etcd with the given args on the agent machine.
	Start(args ...string) (int, error)
	// Stop stops the existing etcd the agent started.
	Stop() error
	// Restart restarts the existing etcd the agent stopped.
	Restart() (int, error)
	// Cleanup stops the exiting etcd the agent started, then archives log and its data dir.
	Cleanup() error
	// Terminate stops the exiting etcd the agent started and removes its data dir.
	Terminate() error
	// DropPort drops all network packets at the given port.
	DropPort(port int) error
	// RecoverPort stops dropping all network packets at the given port.
	RecoverPort(port int) error
	// Status returns the status of etcd on the agent
	Status() (Status, error)
}

type Status struct {
	// TODO: gather more informations
	// TODO: memory usage, raft information, etc..
	State string
}