upgrader

type Interface interface {
	// Upgrade runs in the boot process and performs the function of upgrade
	// for the current operator.
	//
	// Implemention of this interface must be idempotent. If it fails, the
	// program can be restarted to retry again without affecting current
	// Kubernetes cluster and TiDB clusters.
	//
	// Note that it's possible that it cann't finish its job when you're trying
	// to upgrade a newer operator to an older one or enable/disable some
	// irreversible features.
	Upgrade() error
}