func upgradeMongoWatcher(st *state.State, stopch <-chan struct{}, machineID string, maybeStopMongo StopMongo) error {
	m, err := st.Machine(machineID)
	if err != nil {
		return errors.Annotatef(err, "cannot start watcher for machine %q", machineID)
	}
	watch := m.Watch()
	defer func() {
		watch.Kill()
		watch.Wait()
	}()

	for {
		select {
		case <-watch.Changes():
			if err := m.Refresh(); err != nil {
				return errors.Annotate(err, "cannot refresh machine information")
			}
			if !m.IsManager() {
				continue
			}
			expectedVersion, err := m.StopMongoUntilVersion()
			if err != nil {
				return errors.Annotate(err, "cannot obtain minimum version of mongo")
			}
			if expectedVersion == mongo.Mongo24 {
				continue
			}
			var isMaster bool
			isMaster, err = mongo.IsMaster(st.MongoSession(), m)
			if err != nil {
				return errors.Annotatef(err, "cannot determine if machine %q is master", machineID)
			}

			err = maybeStopMongo(expectedVersion, isMaster)
			if err != nil {
				return errors.Annotate(err, "cannot determine if mongo must be stopped")
			}
			if !isMaster {
				addrs := make([]string, len(m.Addresses()))
				ssi, err := st.StateServingInfo()
				if err != nil {
					return errors.Annotate(err, "cannot obtain state serving info to stop mongo")
				}
				for i, addr := range m.Addresses() {
					addrs[i] = net.JoinHostPort(addr.Value, strconv.Itoa(ssi.StatePort))
				}
				if err := replicaset.Remove(st.MongoSession(), addrs...); err != nil {
					return errors.Annotatef(err, "cannot remove %q from replicaset", m.Id())
				}
				if err := m.SetStopMongoUntilVersion(mongo.Mongo24); err != nil {
					return errors.Annotate(err, "cannot reset stop mongo flag")
				}
			}
		case <-stopch:
			return nil
		}
	}
}

// SetUpgradeMongoMode writes a value in the state server to be picked up
// by api servers to know that there is an upgrade ready to happen.
func (st *State) SetUpgradeMongoMode(v mongo.Version) (UpgradeMongoParams, error) {
	currentInfo, err := st.ControllerInfo()
	if err != nil {
		return UpgradeMongoParams{}, errors.Annotate(err, "could not obtain current controller information")
	}
	result := UpgradeMongoParams{}
	machines := []*Machine{}
	for _, mID := range currentInfo.VotingMachineIds {
		m, err := st.Machine(mID)
		if err != nil {
			return UpgradeMongoParams{}, errors.Annotate(err, "cannot change all the replicas")
		}
		isMaster, err := mongo.IsMaster(st.session, m)
		if err != nil {
			return UpgradeMongoParams{}, errors.Annotatef(err, "cannot determine if machine %q is master", mID)
		}
		paddr, err := m.PublicAddress()
		if err != nil {
			return UpgradeMongoParams{}, errors.Annotatef(err, "cannot obtain public address for machine: %v", m)
		}
		tag := m.Tag()
		mtag := tag.(names.MachineTag)
		member := HAMember{
			Tag:           mtag.Id(),
			PublicAddress: paddr,
			Series:        m.Series(),
		}
		if isMaster {
			result.Master = member
		} else {
			result.Members = append(result.Members, member)
		}
		machines = append(machines, m)
	}
	rsMembers, err := replicaset.CurrentMembers(st.session)
	if err != nil {
		return UpgradeMongoParams{}, errors.Annotate(err, "cannot obtain current replicaset members")
	}
	masterRs, err := replicaset.MasterHostPort(st.session)
	if err != nil {
		return UpgradeMongoParams{}, errors.Annotate(err, "cannot determine master on replicaset members")
	}
	for _, m := range rsMembers {
		if m.Address != masterRs {
			result.RsMembers = append(result.RsMembers, m)
		}
	}
	for _, m := range machines {
		if err := m.SetStopMongoUntilVersion(v); err != nil {
			return UpgradeMongoParams{}, errors.Annotate(err, "cannot trigger replica shutdown")
		}
	}
	return result, nil
}

func isMachineMaster(st *state.State, tag names.MachineTag) (bool, error) {
	if st == nil {
		// If there is no state, we aren't a master.
		return false, nil
	}
	// Not calling the agent openState method as it does other checks
	// we really don't care about here.  All we need here is the machine
	// so we can determine if we are the master or not.
	machine, err := st.Machine(tag.Id())
	if err != nil {
		// This shouldn't happen, and if it does, the state worker will have
		// found out before us, and already errored, or is likely to error out
		// very shortly.  All we do here is return the error. The state worker
		// returns an error that will cause the agent to be terminated.
		return false, errors.Trace(err)
	}
	isMaster, err := mongo.IsMaster(st.MongoSession(), machine)
	if err != nil {
		return false, errors.Trace(err)
	}
	return isMaster, nil
}

	if st == nil {
		// If there is no state, we aren't a master.
		return false, nil
	}
	// Not calling the agent openState method as it does other checks
	// we really don't care about here.  All we need here is the machine
	// so we can determine if we are the master or not.
	machine, err := st.Machine(machineId)
	if err != nil {
		// This shouldn't happen, and if it does, the state worker will have
		// found out before us, and already errored, or is likely to error out
		// very shortly.  All we do here is return the error. The state worker
		// returns an error that will cause the agent to be terminated.
		return false, errors.Trace(err)
	}
	isMaster, err := mongo.IsMaster(st.MongoSession(), machine)
	if err != nil {
		return false, errors.Trace(err)
	}
	return isMaster, nil
}

var getUpgradeRetryStrategy = func() utils.AttemptStrategy {
	return utils.AttemptStrategy{
		Delay: 2 * time.Minute,
		Min:   5,
	}
}

// jobsToTargets determines the upgrade targets corresponding to the
// jobs assigned to a machine agent. This determines the upgrade steps