type Config struct {
	// The inclusion of TypeMeta is to ensure future compatibility if the
	// Config object was populated directly via a Kubernetes API mechanism.
	//
	// For example, instead of the custom implementation here, the
	// configuration could be obtained from an API that unifies
	// command-line flags, config-map, etc mechanisms.
	types.TypeMeta

	// Map of federation names that the cluster in which this kube-dns
	// is running belongs to, to the corresponding domain names.
	Federations map[string]string `json:"federations"`
}

type MockSync struct {
	// Config that will be returned from Once().
	Config *Config
	// Error that will be returned from Once().
	Error error

	// Chan to send new configurations on.
	Chan chan *Config
}

type Sync interface {
	// Once does a blocking synchronization of the config map. If the
	// ConfigMap fails to validate, this method will return nil, err.
	Once() (*Config, error)

	// Start a periodic synchronization of the configuration map. When a
	// successful configuration map update is detected, the
	// configuration will be sent to the channel.
	//
	// It is an error to call this more than once.
	Periodic() <-chan *Config
}