func (p *JujuProvisioner) removeUnit(app provision.App, unit provision.AppUnit) error {
	var (
		buf bytes.Buffer
		err error
	)
	cmd := []string{"remove-unit", unit.GetName()}
	// Sometimes juju gives the "no node" error. This is one of Zookeeper bad
	// behaviors. Let's try it multiple times before raising the error to the
	// user, and hope that someday we run away from Zookeeper.
	for i := 0; i < destroyTries; i++ {
		buf.Reset()
		err = runCmd(false, &buf, &buf, cmd...)
		if err != nil && unitNotFound(unit.GetName(), buf.Bytes()) {
			err = nil
		}
		if err == nil {
			break
		}
	}
	if err != nil {
		return cmdError(buf.String(), err, cmd)
	}
	if p.elbSupport() {
		pUnit := provision.Unit{
			Name:       unit.GetName(),
			InstanceId: unit.GetInstanceId(),
		}
		err = p.LoadBalancer().Deregister(app, pUnit)
	}
	conn, collection := p.unitsCollection()
	defer conn.Close()
	collection.RemoveId(unit.GetName())
	go p.terminateMachines(app, unit)
	return err
}

func (p *JujuProvisioner) RemoveUnit(app provision.App, name string) error {
	var unit provision.AppUnit
	for _, unit = range app.ProvisionedUnits() {
		if unit.GetName() == name {
			break
		}
	}
	if unit.GetName() != name {
		return fmt.Errorf("App %q does not have a unit named %q.", app.GetName(), name)
	}
	return p.removeUnit(app, unit)
}

// unbindUnit unbinds a unit from all service instances that are bound to the
// app. It is used by RemoveUnit and RemoveUnits methods.
func (app *App) unbindUnit(unit provision.AppUnit) error {
	conn, err := db.Conn()
	if err != nil {
		return err
	}
	defer conn.Close()
	var instances []service.ServiceInstance
	q := bson.M{"apps": bson.M{"$in": []string{app.Name}}}
	err = conn.ServiceInstances().Find(q).All(&instances)
	if err != nil {
		return err
	}
	for _, instance := range instances {
		err = instance.UnbindUnit(unit)
		if err != nil {
			log.Printf("Error unbinding the unit %s with the service instance %s.", unit.GetIp(), instance.Name)
		}
	}
	return nil
}