@Override
  public void start(final IJobUpdate update, final AuditData auditData)
      throws UpdateStateException {

    requireNonNull(update);
    requireNonNull(auditData);

    storage.write(
        (NoResult<UpdateStateException>)
            storeProvider -> {
              IJobUpdateSummary summary = update.getSummary();
              IJobUpdateInstructions instructions = update.getInstructions();
              IJobKey job = summary.getKey().getJob();

              // Validate the update configuration by making sure we can create an updater for it.
              updateFactory.newUpdate(update.getInstructions(), true);

              if (instructions.getInitialState().isEmpty() && !instructions.isSetDesiredState()) {
                throw new IllegalArgumentException("Update instruction is a no-op.");
              }

              List<IJobUpdateSummary> activeJobUpdates =
                  storeProvider.getJobUpdateStore().fetchJobUpdateSummaries(queryActiveByJob(job));
              if (!activeJobUpdates.isEmpty()) {
                throw new UpdateStateException(
                    "An active update already exists for this job, "
                        + "please terminate it before starting another. "
                        + "Active updates are those in states "
                        + Updates.ACTIVE_JOB_UPDATE_STATES);
              }

              LOG.info("Starting update for job " + job);
              ILock lock;
              try {
                lock =
                    lockManager.acquireLock(
                        ILockKey.build(LockKey.job(job.newBuilder())), auditData.getUser());
              } catch (LockException e) {
                throw new UpdateStateException(e.getMessage(), e);
              }

              storeProvider
                  .getJobUpdateStore()
                  .saveJobUpdate(update, Optional.of(requireNonNull(lock.getToken())));

              JobUpdateStatus status = ROLLING_FORWARD;
              if (isCoordinatedUpdate(instructions)) {
                status = ROLL_FORWARD_AWAITING_PULSE;
                pulseHandler.initializePulseState(update, status);
              }

              recordAndChangeJobUpdateStatus(
                  storeProvider, summary.getKey(), addAuditData(newEvent(status), auditData));
            });
  }
  @Override
  public void systemResume() {
    storage.write(
        (NoResult.Quiet)
            storeProvider -> {
              for (IJobUpdateDetails details :
                  storeProvider.getJobUpdateStore().fetchJobUpdateDetails(ACTIVE_QUERY)) {

                IJobUpdateSummary summary = details.getUpdate().getSummary();
                IJobUpdateInstructions instructions = details.getUpdate().getInstructions();
                IJobUpdateKey key = summary.getKey();
                JobUpdateStatus status = summary.getState().getStatus();

                if (isCoordinatedUpdate(instructions)) {
                  LOG.info("Automatically restoring pulse state for " + key);
                  pulseHandler.initializePulseState(details.getUpdate(), status);
                }

                if (AUTO_RESUME_STATES.contains(status)) {
                  LOG.info("Automatically resuming update " + key);

                  try {
                    changeJobUpdateStatus(storeProvider, key, newEvent(status), false);
                  } catch (UpdateStateException e) {
                    throw Throwables.propagate(e);
                  }
                }
              }
            });
  }
  private void changeUpdateStatus(
      MutableStoreProvider storeProvider, IJobUpdateSummary updateSummary, JobUpdateEvent event)
      throws UpdateStateException {

    if (updateSummary.getState().getStatus() == event.getStatus()) {
      return;
    }

    assertTransitionAllowed(updateSummary.getState().getStatus(), event.getStatus());
    recordAndChangeJobUpdateStatus(storeProvider, updateSummary.getKey(), event);
  }
  private void evaluateUpdater(
      final MutableStoreProvider storeProvider,
      final UpdateFactory.Update update,
      IJobUpdateSummary summary,
      Map<Integer, Optional<IScheduledTask>> changedInstance)
      throws UpdateStateException {

    JobUpdateStatus updaterStatus = summary.getState().getStatus();
    final IJobUpdateKey key = summary.getKey();

    JobUpdateStore.Mutable updateStore = storeProvider.getJobUpdateStore();
    if (!updateStore.getLockToken(key).isPresent()) {
      recordAndChangeJobUpdateStatus(
          storeProvider, key, newEvent(ERROR).setMessage(LOST_LOCK_MESSAGE));
      return;
    }

    IJobUpdateInstructions instructions = updateStore.fetchJobUpdateInstructions(key).get();
    if (isCoordinatedAndPulseExpired(key, instructions)) {
      // Move coordinated update into awaiting pulse state.
      JobUpdateStatus blockedStatus = getBlockedState(summary.getState().getStatus());
      changeUpdateStatus(
          storeProvider, summary, newEvent(blockedStatus).setMessage(PULSE_TIMEOUT_MESSAGE));
      return;
    }

    InstanceStateProvider<Integer, Optional<IScheduledTask>> stateProvider =
        instanceId -> getActiveInstance(storeProvider.getTaskStore(), key.getJob(), instanceId);

    EvaluationResult<Integer> result = update.getUpdater().evaluate(changedInstance, stateProvider);

    LOG.info(key + " evaluation result: " + result);

    for (Map.Entry<Integer, SideEffect> entry : result.getSideEffects().entrySet()) {
      Iterable<InstanceUpdateStatus> statusChanges;

      int instanceId = entry.getKey();
      List<IJobInstanceUpdateEvent> savedEvents = updateStore.fetchInstanceEvents(key, instanceId);

      Set<JobUpdateAction> savedActions =
          FluentIterable.from(savedEvents).transform(EVENT_TO_ACTION).toSet();

      // Don't bother persisting a sequence of status changes that represents an instance that
      // was immediately recognized as being healthy and in the desired state.
      if (entry.getValue().getStatusChanges().equals(NOOP_INSTANCE_UPDATE)
          && savedEvents.isEmpty()) {

        LOG.info("Suppressing no-op update for instance " + instanceId);
        statusChanges = ImmutableSet.of();
      } else {
        statusChanges = entry.getValue().getStatusChanges();
      }

      for (InstanceUpdateStatus statusChange : statusChanges) {
        JobUpdateAction action = STATE_MAP.get(Pair.of(statusChange, updaterStatus));
        requireNonNull(action);

        // A given instance update action may only be issued once during the update lifecycle.
        // Suppress duplicate events due to pause/resume operations.
        if (savedActions.contains(action)) {
          LOG.info(
              String.format(
                  "Suppressing duplicate update %s for instance %s.", action, instanceId));
        } else {
          IJobInstanceUpdateEvent event =
              IJobInstanceUpdateEvent.build(
                  new JobInstanceUpdateEvent()
                      .setInstanceId(instanceId)
                      .setTimestampMs(clock.nowMillis())
                      .setAction(action));
          updateStore.saveJobInstanceUpdateEvent(summary.getKey(), event);
        }
      }
    }

    OneWayStatus status = result.getStatus();
    if (status == SUCCEEDED || status == OneWayStatus.FAILED) {
      if (SideEffect.hasActions(result.getSideEffects().values())) {
        throw new IllegalArgumentException(
            "A terminal state should not specify actions: " + result);
      }

      JobUpdateEvent event = new JobUpdateEvent();
      if (status == SUCCEEDED) {
        event.setStatus(update.getSuccessStatus());
      } else {
        event.setStatus(update.getFailureStatus());
        // Generate a transition message based on one (arbitrary) instance in the group that pushed
        // the update over the failure threshold (in all likelihood this group is of size 1).
        // This is done as a rough cut to aid in diagnosing a failed update, as generating a
        // complete summary would likely be of dubious value.
        for (Map.Entry<Integer, SideEffect> entry : result.getSideEffects().entrySet()) {
          Optional<Failure> failure = entry.getValue().getFailure();
          if (failure.isPresent()) {
            event.setMessage(failureMessage(entry.getKey(), failure.get()));
            break;
          }
        }
      }
      changeUpdateStatus(storeProvider, summary, event);
    } else {
      LOG.info("Executing side-effects for update of " + key + ": " + result.getSideEffects());
      for (Map.Entry<Integer, SideEffect> entry : result.getSideEffects().entrySet()) {
        IInstanceKey instance = InstanceKeys.from(key.getJob(), entry.getKey());

        Optional<InstanceAction> action = entry.getValue().getAction();
        if (action.isPresent()) {
          Optional<InstanceActionHandler> handler = action.get().getHandler();
          if (handler.isPresent()) {
            Optional<Amount<Long, Time>> reevaluateDelay =
                handler
                    .get()
                    .getReevaluationDelay(
                        instance, instructions, storeProvider, stateManager, updaterStatus);
            if (reevaluateDelay.isPresent()) {
              executor.schedule(
                  getDeferredEvaluator(instance, key),
                  reevaluateDelay.get().getValue(),
                  reevaluateDelay.get().getUnit().getTimeUnit());
            }
          }
        }
      }
    }
  }