github.com/jrxfive/nomad@v0.6.1-0.20170802162750-1fef470e89bf/client/task_runner.go

package client

import (
	"bytes"
	"crypto/md5"
	"encoding/hex"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/armon/go-metrics"
	"github.com/boltdb/bolt"
	"github.com/golang/snappy"
	"github.com/hashicorp/consul-template/signals"
	"github.com/hashicorp/go-multierror"
	version "github.com/hashicorp/go-version"
	"github.com/hashicorp/nomad/client/allocdir"
	"github.com/hashicorp/nomad/client/config"
	"github.com/hashicorp/nomad/client/driver"
	"github.com/hashicorp/nomad/client/getter"
	"github.com/hashicorp/nomad/client/vaultclient"
	"github.com/hashicorp/nomad/nomad/structs"
	"github.com/ugorji/go/codec"

	"github.com/hashicorp/nomad/client/driver/env"
	dstructs "github.com/hashicorp/nomad/client/driver/structs"
	cstructs "github.com/hashicorp/nomad/client/structs"
)

const (
	// killBackoffBaseline is the baseline time for exponential backoff while
	// killing a task.
	killBackoffBaseline = 5 * time.Second

	// killBackoffLimit is the limit of the exponential backoff for killing
	// the task.
	killBackoffLimit = 2 * time.Minute

	// killFailureLimit is how many times we will attempt to kill a task before
	// giving up and potentially leaking resources.
	killFailureLimit = 5

	// vaultBackoffBaseline is the baseline time for exponential backoff when
	// attempting to retrieve a Vault token
	vaultBackoffBaseline = 5 * time.Second

	// vaultBackoffLimit is the limit of the exponential backoff when attempting
	// to retrieve a Vault token
	vaultBackoffLimit = 3 * time.Minute

	// vaultTokenFile is the name of the file holding the Vault token inside the
	// task's secret directory
	vaultTokenFile = "vault_token"
)

var (
	// taskRunnerStateAllKey holds all the task runners state. At the moment
	// there is no need to split it
	taskRunnerStateAllKey = []byte("simple-all")
)

// TaskRunner is used to wrap a task within an allocation and provide the execution context.
type TaskRunner struct {
	stateDB        *bolt.DB
	config         *config.Config
	updater        TaskStateUpdater
	logger         *log.Logger
	alloc          *structs.Allocation
	restartTracker *RestartTracker
	consul         ConsulServiceAPI

	// running marks whether the task is running
	running     bool
	runningLock sync.Mutex

	resourceUsage     *cstructs.TaskResourceUsage
	resourceUsageLock sync.RWMutex

	task    *structs.Task
	taskDir *allocdir.TaskDir

	// envBuilder is used to build the task's environment
	envBuilder *env.Builder

	// driverNet is the network information returned by the driver
	driverNet     *cstructs.DriverNetwork
	driverNetLock sync.Mutex

	// updateCh is used to receive updated versions of the allocation
	updateCh chan *structs.Allocation

	handle     driver.DriverHandle
	handleLock sync.Mutex

	// artifactsDownloaded tracks whether the tasks artifacts have been
	// downloaded
	//
	// Must acquire persistLock when accessing
	artifactsDownloaded bool

	// taskDirBuilt tracks whether the task has built its directory.
	//
	// Must acquire persistLock when accessing
	taskDirBuilt bool

	// createdResources are all the resources created by the task driver
	// across all attempts to start the task.
	// Simple gets and sets should use {get,set}CreatedResources
	createdResources     *driver.CreatedResources
	createdResourcesLock sync.Mutex

	// payloadRendered tracks whether the payload has been rendered to disk
	payloadRendered bool

	// vaultFuture is the means to wait for and get a Vault token
	vaultFuture *tokenFuture

	// recoveredVaultToken is the token that was recovered through a restore
	recoveredVaultToken string

	// vaultClient is used to retrieve and renew any needed Vault token
	vaultClient vaultclient.VaultClient

	// templateManager is used to manage any consul-templates this task may have
	templateManager *TaskTemplateManager

	// startCh is used to trigger the start of the task
	startCh chan struct{}

	// unblockCh is used to unblock the starting of the task
	unblockCh   chan struct{}
	unblocked   bool
	unblockLock sync.Mutex

	// restartCh is used to restart a task
	restartCh chan *structs.TaskEvent

	// signalCh is used to send a signal to a task
	signalCh chan SignalEvent

	destroy      bool
	destroyCh    chan struct{}
	destroyLock  sync.Mutex
	destroyEvent *structs.TaskEvent

	// waitCh closing marks the run loop as having exited
	waitCh chan struct{}

	// persistLock must be acquired when accessing fields stored by
	// SaveState. SaveState is called asynchronously to TaskRunner.Run by
	// AllocRunner, so all state fields must be synchronized using this
	// lock.
	persistLock sync.Mutex

	// persistedHash is the hash of the last persisted snapshot. It is used to
	// detect if a new snapshot has to be writen to disk.
	persistedHash []byte
}

// taskRunnerState is used to snapshot the state of the task runner
type taskRunnerState struct {
	Version            string
	HandleID           string
	ArtifactDownloaded bool
	TaskDirBuilt       bool
	PayloadRendered    bool
	CreatedResources   *driver.CreatedResources
	DriverNetwork      *cstructs.DriverNetwork
}

func (s *taskRunnerState) Hash() []byte {
	h := md5.New()

	io.WriteString(h, s.Version)
	io.WriteString(h, s.HandleID)
	io.WriteString(h, fmt.Sprintf("%v", s.ArtifactDownloaded))
	io.WriteString(h, fmt.Sprintf("%v", s.TaskDirBuilt))
	io.WriteString(h, fmt.Sprintf("%v", s.PayloadRendered))
	h.Write(s.CreatedResources.Hash())
	h.Write(s.DriverNetwork.Hash())

	return h.Sum(nil)
}

// TaskStateUpdater is used to signal that tasks state has changed.
type TaskStateUpdater func(taskName, state string, event *structs.TaskEvent)

// SignalEvent is a tuple of the signal and the event generating it
type SignalEvent struct {
	// s is the signal to be sent
	s os.Signal

	// e is the task event generating the signal
	e *structs.TaskEvent

	// result should be used to send back the result of the signal
	result chan<- error
}

// NewTaskRunner is used to create a new task context
func NewTaskRunner(logger *log.Logger, config *config.Config,
	stateDB *bolt.DB, updater TaskStateUpdater, taskDir *allocdir.TaskDir,
	alloc *structs.Allocation, task *structs.Task,
	vaultClient vaultclient.VaultClient, consulClient ConsulServiceAPI) *TaskRunner {

	// Merge in the task resources
	task.Resources = alloc.TaskResources[task.Name]

	// Build the restart tracker.
	tg := alloc.Job.LookupTaskGroup(alloc.TaskGroup)
	if tg == nil {
		logger.Printf("[ERR] client: alloc '%s' for missing task group '%s'", alloc.ID, alloc.TaskGroup)
		return nil
	}
	restartTracker := newRestartTracker(tg.RestartPolicy, alloc.Job.Type)

	// Initialize the environment builder
	envBuilder := env.NewBuilder(config.Node, alloc, task, config.Region)

	tc := &TaskRunner{
		config:           config,
		stateDB:          stateDB,
		updater:          updater,
		logger:           logger,
		restartTracker:   restartTracker,
		alloc:            alloc,
		task:             task,
		taskDir:          taskDir,
		envBuilder:       envBuilder,
		createdResources: driver.NewCreatedResources(),
		consul:           consulClient,
		vaultClient:      vaultClient,
		vaultFuture:      NewTokenFuture().Set(""),
		updateCh:         make(chan *structs.Allocation, 64),
		destroyCh:        make(chan struct{}),
		waitCh:           make(chan struct{}),
		startCh:          make(chan struct{}, 1),
		unblockCh:        make(chan struct{}),
		restartCh:        make(chan *structs.TaskEvent),
		signalCh:         make(chan SignalEvent),
	}

	return tc
}

// MarkReceived marks the task as received.
func (r *TaskRunner) MarkReceived() {
	r.updater(r.task.Name, structs.TaskStatePending, structs.NewTaskEvent(structs.TaskReceived))
}

// WaitCh returns a channel to wait for termination
func (r *TaskRunner) WaitCh() <-chan struct{} {
	return r.waitCh
}

// getHandle returns the task's handle or nil
func (r *TaskRunner) getHandle() driver.DriverHandle {
	r.handleLock.Lock()
	h := r.handle
	r.handleLock.Unlock()
	return h
}

// pre060StateFilePath returns the path to our state file that would have been
// written pre v0.6.0
// COMPAT: Remove in 0.7.0
func (r *TaskRunner) pre060StateFilePath() string {
	// Get the MD5 of the task name
	hashVal := md5.Sum([]byte(r.task.Name))
	hashHex := hex.EncodeToString(hashVal[:])
	dirName := fmt.Sprintf("task-%s", hashHex)

	// Generate the path
	return filepath.Join(r.config.StateDir, "alloc", r.alloc.ID, dirName, "state.json")
}

// RestoreState is used to restore our state. If a non-empty string is returned
// the task is restarted with the string as the reason. This is useful for
// backwards incompatible upgrades that need to restart tasks with a new
// executor.
func (r *TaskRunner) RestoreState() (string, error) {
	// COMPAT: Remove in 0.7.0
	// 0.6.0 transistioned from individual state files to a single bolt-db.
	// The upgrade path is to:
	// Check if old state exists
	//   If so, restore from that and delete old state
	// Restore using state database

	var snap taskRunnerState

	// Check if the old snapshot is there
	oldPath := r.pre060StateFilePath()
	if err := pre060RestoreState(oldPath, &snap); err == nil {
		// Delete the old state
		os.RemoveAll(oldPath)
	} else if !os.IsNotExist(err) {
		// Something corrupt in the old state file
		return "", err
	} else {
		// We are doing a normal restore
		err := r.stateDB.View(func(tx *bolt.Tx) error {
			bkt, err := getTaskBucket(tx, r.alloc.ID, r.task.Name)
			if err != nil {
				return fmt.Errorf("failed to get task bucket: %v", err)
			}

			if err := getObject(bkt, taskRunnerStateAllKey, &snap); err != nil {
				return fmt.Errorf("failed to read task runner state: %v", err)
			}
			return nil
		})
		if err != nil {
			return "", err
		}

	}

	// Restore fields from the snapshot
	r.artifactsDownloaded = snap.ArtifactDownloaded
	r.taskDirBuilt = snap.TaskDirBuilt
	r.payloadRendered = snap.PayloadRendered
	r.setCreatedResources(snap.CreatedResources)
	r.driverNet = snap.DriverNetwork

	if r.task.Vault != nil {
		// Read the token from the secret directory
		tokenPath := filepath.Join(r.taskDir.SecretsDir, vaultTokenFile)
		data, err := ioutil.ReadFile(tokenPath)
		if err != nil {
			if !os.IsNotExist(err) {
				return "", fmt.Errorf("failed to read token for task %q in alloc %q: %v", r.task.Name, r.alloc.ID, err)
			}

			// Token file doesn't exist
		} else {
			// Store the recovered token
			r.recoveredVaultToken = string(data)
		}
	}

	// Restore the driver
	restartReason := ""
	if snap.HandleID != "" {
		d, err := r.createDriver()
		if err != nil {
			return "", err
		}

		// Add the restored network driver to the environment
		r.envBuilder.SetDriverNetwork(r.driverNet)

		// Open a connection to the driver handle
		ctx := driver.NewExecContext(r.taskDir, r.envBuilder.Build())
		handle, err := d.Open(ctx, snap.HandleID)

		// In the case it fails, we relaunch the task in the Run() method.
		if err != nil {
			r.logger.Printf("[ERR] client: failed to open handle to task %q for alloc %q: %v",
				r.task.Name, r.alloc.ID, err)
			return "", nil
		}

		if pre06ScriptCheck(snap.Version, r.task.Driver, r.task.Services) {
			restartReason = pre06ScriptCheckReason
		}

		if err := r.registerServices(d, handle, r.driverNet); err != nil {
			// Don't hard fail here as there's a chance this task
			// registered with Consul properly when it initial
			// started.
			r.logger.Printf("[WARN] client: failed to register services and checks with consul for task %q in alloc %q: %v",
				r.task.Name, r.alloc.ID, err)
		}

		r.handleLock.Lock()
		r.handle = handle
		r.handleLock.Unlock()

		r.runningLock.Lock()
		r.running = true
		r.runningLock.Unlock()
	}
	return restartReason, nil
}

// ver06 is used for checking for pre-0.6 script checks
var ver06 = version.Must(version.NewVersion("0.6.0dev"))

// pre06ScriptCheckReason is the restart reason given when a pre-0.6 script
// check is found on an exec/java task.
const pre06ScriptCheckReason = "upgrading pre-0.6 script checks"

// pre06ScriptCheck returns true if version is prior to 0.6.0dev, has a script
// check, and uses exec or java drivers.
func pre06ScriptCheck(ver, driver string, services []*structs.Service) bool {
	if driver != "exec" && driver != "java" && driver != "mock_driver" {
		// Only exec and java are affected
		return false
	}
	v, err := version.NewVersion(ver)
	if err != nil {
		// Treat it as old
		return true
	}
	if !v.LessThan(ver06) {
		// >= 0.6.0dev
		return false
	}
	for _, service := range services {
		for _, check := range service.Checks {
			if check.Type == "script" {
				return true
			}
		}
	}
	return false
}

// SaveState is used to snapshot our state
func (r *TaskRunner) SaveState() error {
	r.destroyLock.Lock()
	defer r.destroyLock.Unlock()
	if r.destroy {
		// Don't save state if already destroyed
		return nil
	}

	r.persistLock.Lock()
	defer r.persistLock.Unlock()
	snap := taskRunnerState{
		Version:            r.config.Version,
		ArtifactDownloaded: r.artifactsDownloaded,
		TaskDirBuilt:       r.taskDirBuilt,
		PayloadRendered:    r.payloadRendered,
		CreatedResources:   r.getCreatedResources(),
	}

	r.handleLock.Lock()
	if r.handle != nil {
		snap.HandleID = r.handle.ID()
	}
	r.handleLock.Unlock()

	r.driverNetLock.Lock()
	snap.DriverNetwork = r.driverNet.Copy()
	r.driverNetLock.Unlock()

	// If nothing has changed avoid the write
	h := snap.Hash()
	if bytes.Equal(h, r.persistedHash) {
		return nil
	}

	// Serialize the object
	var buf bytes.Buffer
	if err := codec.NewEncoder(&buf, structs.MsgpackHandle).Encode(&snap); err != nil {
		return fmt.Errorf("failed to serialize snapshot: %v", err)
	}

	// Start the transaction.
	return r.stateDB.Batch(func(tx *bolt.Tx) error {
		// Grab the task bucket
		taskBkt, err := getTaskBucket(tx, r.alloc.ID, r.task.Name)
		if err != nil {
			return fmt.Errorf("failed to retrieve allocation bucket: %v", err)
		}

		if err := putData(taskBkt, taskRunnerStateAllKey, buf.Bytes()); err != nil {
			return fmt.Errorf("failed to write task_runner state: %v", err)
		}

		// Store the hash that was persisted
		tx.OnCommit(func() {
			r.persistedHash = h
		})

		return nil
	})
}

// DestroyState is used to cleanup after ourselves
func (r *TaskRunner) DestroyState() error {
	r.persistLock.Lock()
	defer r.persistLock.Unlock()

	return r.stateDB.Update(func(tx *bolt.Tx) error {
		if err := deleteTaskBucket(tx, r.alloc.ID, r.task.Name); err != nil {
			return fmt.Errorf("failed to delete task bucket: %v", err)
		}
		return nil
	})
}

// setState is used to update the state of the task runner
func (r *TaskRunner) setState(state string, event *structs.TaskEvent) {
	// Persist our state to disk.
	if err := r.SaveState(); err != nil {
		r.logger.Printf("[ERR] client: failed to save state of Task Runner for task %q: %v", r.task.Name, err)
	}

	// Indicate the task has been updated.
	r.updater(r.task.Name, state, event)
}

// createDriver makes a driver for the task
func (r *TaskRunner) createDriver() (driver.Driver, error) {
	// Create a task-specific event emitter callback to expose minimal
	// state to drivers
	eventEmitter := func(m string, args ...interface{}) {
		msg := fmt.Sprintf(m, args...)
		r.logger.Printf("[DEBUG] client: driver event for alloc %q: %s", r.alloc.ID, msg)
		r.setState(structs.TaskStatePending, structs.NewTaskEvent(structs.TaskDriverMessage).SetDriverMessage(msg))
	}

	driverCtx := driver.NewDriverContext(r.task.Name, r.alloc.ID, r.config, r.config.Node, r.logger, eventEmitter)
	d, err := driver.NewDriver(r.task.Driver, driverCtx)
	if err != nil {
		return nil, fmt.Errorf("failed to create driver '%s' for alloc %s: %v",
			r.task.Driver, r.alloc.ID, err)
	}

	return d, err
}

// Run is a long running routine used to manage the task
func (r *TaskRunner) Run() {
	defer close(r.waitCh)
	r.logger.Printf("[DEBUG] client: starting task context for '%s' (alloc '%s')",
		r.task.Name, r.alloc.ID)

	if err := r.validateTask(); err != nil {
		r.setState(
			structs.TaskStateDead,
			structs.NewTaskEvent(structs.TaskFailedValidation).SetValidationError(err).SetFailsTask())
		return
	}

	// Create a temporary driver so that we can determine the FSIsolation
	// required. run->startTask will create a new driver after environment
	// has been setup (env vars, templates, artifacts, secrets, etc).
	tmpDrv, err := r.createDriver()
	if err != nil {
		e := fmt.Errorf("failed to create driver of task %q for alloc %q: %v", r.task.Name, r.alloc.ID, err)
		r.setState(
			structs.TaskStateDead,
			structs.NewTaskEvent(structs.TaskSetupFailure).SetSetupError(e).SetFailsTask())
		return
	}

	// Build base task directory structure regardless of FS isolation abilities.
	// This needs to happen before we start the Vault manager and call prestart
	// as both those can write to the task directories
	if err := r.buildTaskDir(tmpDrv.FSIsolation()); err != nil {
		e := fmt.Errorf("failed to build task directory for %q: %v", r.task.Name, err)
		r.setState(
			structs.TaskStateDead,
			structs.NewTaskEvent(structs.TaskSetupFailure).SetSetupError(e).SetFailsTask())
		return
	}

	// If there is no Vault policy leave the static future created in
	// NewTaskRunner
	if r.task.Vault != nil {
		// Start the go-routine to get a Vault token
		r.vaultFuture.Clear()
		go r.vaultManager(r.recoveredVaultToken)
	}

	// Start the run loop
	r.run()

	// Do any cleanup necessary
	r.postrun()

	return
}

// validateTask validates the fields of the task and returns an error if the
// task is invalid.
func (r *TaskRunner) validateTask() error {
	var mErr multierror.Error

	// Validate the user.
	unallowedUsers := r.config.ReadStringListToMapDefault("user.blacklist", config.DefaultUserBlacklist)
	checkDrivers := r.config.ReadStringListToMapDefault("user.checked_drivers", config.DefaultUserCheckedDrivers)
	if _, driverMatch := checkDrivers[r.task.Driver]; driverMatch {
		if _, unallowed := unallowedUsers[r.task.User]; unallowed {
			mErr.Errors = append(mErr.Errors, fmt.Errorf("running as user %q is disallowed", r.task.User))
		}
	}

	// Validate the artifacts
	for i, artifact := range r.task.Artifacts {
		// Verify the artifact doesn't escape the task directory.
		if err := artifact.Validate(); err != nil {
			// If this error occurs there is potentially a server bug or
			// mallicious, server spoofing.
			r.logger.Printf("[ERR] client: allocation %q, task %v, artifact %#v (%v) fails validation: %v",
				r.alloc.ID, r.task.Name, artifact, i, err)
			mErr.Errors = append(mErr.Errors, fmt.Errorf("artifact (%d) failed validation: %v", i, err))
		}
	}

	// Validate the Service names
	taskEnv := r.envBuilder.Build()
	for i, service := range r.task.Services {
		name := taskEnv.ReplaceEnv(service.Name)
		if err := service.ValidateName(name); err != nil {
			mErr.Errors = append(mErr.Errors, fmt.Errorf("service (%d) failed validation: %v", i, err))
		}
	}

	if len(mErr.Errors) == 1 {
		return mErr.Errors[0]
	}
	return mErr.ErrorOrNil()
}

// tokenFuture stores the Vault token and allows consumers to block till a valid
// token exists
type tokenFuture struct {
	waiting []chan struct{}
	token   string
	set     bool
	m       sync.Mutex
}

// NewTokenFuture returns a new token future without any token set
func NewTokenFuture() *tokenFuture {
	return &tokenFuture{}
}

// Wait returns a channel that can be waited on. When this channel unblocks, a
// valid token will be available via the Get method
func (f *tokenFuture) Wait() <-chan struct{} {
	f.m.Lock()
	defer f.m.Unlock()

	c := make(chan struct{})
	if f.set {
		close(c)
		return c
	}

	f.waiting = append(f.waiting, c)
	return c
}

// Set sets the token value and unblocks any caller of Wait
func (f *tokenFuture) Set(token string) *tokenFuture {
	f.m.Lock()
	defer f.m.Unlock()

	f.set = true
	f.token = token
	for _, w := range f.waiting {
		close(w)
	}
	f.waiting = nil
	return f
}

// Clear clears the set vault token.
func (f *tokenFuture) Clear() *tokenFuture {
	f.m.Lock()
	defer f.m.Unlock()

	f.token = ""
	f.set = false
	return f
}

// Get returns the set Vault token
func (f *tokenFuture) Get() string {
	f.m.Lock()
	defer f.m.Unlock()
	return f.token
}

// vaultManager should be called in a go-routine and manages the derivation,
// renewal and handling of errors with the Vault token. The optional parameter
// allows setting the initial Vault token. This is useful when the Vault token
// is recovered off disk.
func (r *TaskRunner) vaultManager(token string) {
	// Helper for stopping token renewal
	stopRenewal := func() {
		if err := r.vaultClient.StopRenewToken(r.vaultFuture.Get()); err != nil {
			r.logger.Printf("[WARN] client: failed to stop token renewal for task %v in alloc %q: %v", r.task.Name, r.alloc.ID, err)
		}
	}

	// updatedToken lets us store state between loops. If true, a new token
	// has been retrieved and we need to apply the Vault change mode
	var updatedToken bool

OUTER:
	for {
		// Check if we should exit
		select {
		case <-r.waitCh:
			stopRenewal()
			return
		default:
		}

		// Clear the token
		r.vaultFuture.Clear()

		// Check if there already is a token which can be the case for
		// restoring the TaskRunner
		if token == "" {
			// Get a token
			var exit bool
			token, exit = r.deriveVaultToken()
			if exit {
				// Exit the manager
				return
			}

			// Write the token to disk
			if err := r.writeToken(token); err != nil {
				e := fmt.Errorf("failed to write Vault token to disk")
				r.logger.Printf("[ERR] client: %v for task %v on alloc %q: %v", e, r.task.Name, r.alloc.ID, err)
				r.Kill("vault", e.Error(), true)
				return
			}
		}

		// Start the renewal process
		renewCh, err := r.vaultClient.RenewToken(token, 30)

		// An error returned means the token is not being renewed
		if err != nil {
			r.logger.Printf("[ERR] client: failed to start renewal of Vault token for task %v on alloc %q: %v", r.task.Name, r.alloc.ID, err)
			token = ""
			goto OUTER
		}

		// The Vault token is valid now, so set it
		r.vaultFuture.Set(token)

		if updatedToken {
			switch r.task.Vault.ChangeMode {
			case structs.VaultChangeModeSignal:
				s, err := signals.Parse(r.task.Vault.ChangeSignal)
				if err != nil {
					e := fmt.Errorf("failed to parse signal: %v", err)
					r.logger.Printf("[ERR] client: %v", err)
					r.Kill("vault", e.Error(), true)
					return
				}

				if err := r.Signal("vault", "new Vault token acquired", s); err != nil {
					r.logger.Printf("[ERR] client: failed to send signal to task %v for alloc %q: %v", r.task.Name, r.alloc.ID, err)
					r.Kill("vault", fmt.Sprintf("failed to send signal to task: %v", err), true)
					return
				}
			case structs.VaultChangeModeRestart:
				r.Restart("vault", "new Vault token acquired")
			case structs.VaultChangeModeNoop:
				fallthrough
			default:
				r.logger.Printf("[ERR] client: Invalid Vault change mode: %q", r.task.Vault.ChangeMode)
			}

			// We have handled it
			updatedToken = false

			// Call the handler
			r.updatedTokenHandler()
		}

		// Start watching for renewal errors
		select {
		case err := <-renewCh:
			// Clear the token
			token = ""
			r.logger.Printf("[ERR] client: failed to renew Vault token for task %v on alloc %q: %v", r.task.Name, r.alloc.ID, err)
			stopRenewal()

			// Check if we have to do anything
			if r.task.Vault.ChangeMode != structs.VaultChangeModeNoop {
				updatedToken = true
			}
		case <-r.waitCh:
			stopRenewal()
			return
		}
	}
}

// deriveVaultToken derives the Vault token using exponential backoffs. It
// returns the Vault token and whether the manager should exit.
func (r *TaskRunner) deriveVaultToken() (token string, exit bool) {
	attempts := 0
	for {
		tokens, err := r.vaultClient.DeriveToken(r.alloc, []string{r.task.Name})
		if err == nil {
			return tokens[r.task.Name], false
		}

		// Check if we can't recover from the error
		if !structs.IsRecoverable(err) {
			r.logger.Printf("[ERR] client: failed to derive Vault token for task %v on alloc %q: %v",
				r.task.Name, r.alloc.ID, err)
			r.Kill("vault", fmt.Sprintf("failed to derive token: %v", err), true)
			return "", true
		}

		// Handle the retry case
		backoff := (1 << (2 * uint64(attempts))) * vaultBackoffBaseline
		if backoff > vaultBackoffLimit {
			backoff = vaultBackoffLimit
		}
		r.logger.Printf("[ERR] client: failed to derive Vault token for task %v on alloc %q: %v; retrying in %v",
			r.task.Name, r.alloc.ID, err, backoff)

		attempts++

		// Wait till retrying
		select {
		case <-r.waitCh:
			return "", true
		case <-time.After(backoff):
		}
	}
}

// writeToken writes the given token to disk
func (r *TaskRunner) writeToken(token string) error {
	tokenPath := filepath.Join(r.taskDir.SecretsDir, vaultTokenFile)
	if err := ioutil.WriteFile(tokenPath, []byte(token), 0777); err != nil {
		return fmt.Errorf("failed to save Vault tokens to secret dir for task %q in alloc %q: %v", r.task.Name, r.alloc.ID, err)
	}

	return nil
}

// updatedTokenHandler is called when a new Vault token is retrieved. Things
// that rely on the token should be updated here.
func (r *TaskRunner) updatedTokenHandler() {

	// Update the tasks environment
	r.envBuilder.SetVaultToken(r.vaultFuture.Get(), r.task.Vault.Env)

	if r.templateManager != nil {
		r.templateManager.Stop()

		// Create a new templateManager
		var err error
		r.templateManager, err = NewTaskTemplateManager(r, r.task.Templates,
			r.config, r.vaultFuture.Get(), r.taskDir.Dir, r.envBuilder)
		if err != nil {
			err := fmt.Errorf("failed to build task's template manager: %v", err)
			r.setState(structs.TaskStateDead, structs.NewTaskEvent(structs.TaskSetupFailure).SetSetupError(err).SetFailsTask())
			r.logger.Printf("[ERR] client: alloc %q, task %q %v", r.alloc.ID, r.task.Name, err)
			r.Kill("vault", err.Error(), true)
			return
		}
	}
}

// prestart handles life-cycle tasks that occur before the task has started.
// Since it's run asynchronously with the main Run() loop the alloc & task are
// passed in to avoid racing with updates.
func (r *TaskRunner) prestart(alloc *structs.Allocation, task *structs.Task, resultCh chan bool) {
	if task.Vault != nil {
		// Wait for the token
		r.logger.Printf("[DEBUG] client: waiting for Vault token for task %v in alloc %q", task.Name, alloc.ID)
		tokenCh := r.vaultFuture.Wait()
		select {
		case <-tokenCh:
		case <-r.waitCh:
			resultCh <- false
			return
		}
		r.logger.Printf("[DEBUG] client: retrieved Vault token for task %v in alloc %q", task.Name, alloc.ID)
		r.envBuilder.SetVaultToken(r.vaultFuture.Get(), task.Vault.Env)
	}

	// If the job is a dispatch job and there is a payload write it to disk
	requirePayload := len(alloc.Job.Payload) != 0 &&
		(r.task.DispatchPayload != nil && r.task.DispatchPayload.File != "")
	if !r.payloadRendered && requirePayload {
		renderTo := filepath.Join(r.taskDir.LocalDir, task.DispatchPayload.File)
		decoded, err := snappy.Decode(nil, alloc.Job.Payload)
		if err != nil {
			r.setState(
				structs.TaskStateDead,
				structs.NewTaskEvent(structs.TaskSetupFailure).SetSetupError(err).SetFailsTask())
			resultCh <- false
			return
		}

		if err := os.MkdirAll(filepath.Dir(renderTo), 07777); err != nil {
			r.setState(
				structs.TaskStateDead,
				structs.NewTaskEvent(structs.TaskSetupFailure).SetSetupError(err).SetFailsTask())
			resultCh <- false
			return
		}

		if err := ioutil.WriteFile(renderTo, decoded, 0777); err != nil {
			r.setState(
				structs.TaskStateDead,
				structs.NewTaskEvent(structs.TaskSetupFailure).SetSetupError(err).SetFailsTask())
			resultCh <- false
			return
		}

		r.payloadRendered = true
	}

	for {
		r.persistLock.Lock()
		downloaded := r.artifactsDownloaded
		r.persistLock.Unlock()

		// Download the task's artifacts
		if !downloaded && len(task.Artifacts) > 0 {
			r.setState(structs.TaskStatePending, structs.NewTaskEvent(structs.TaskDownloadingArtifacts))
			taskEnv := r.envBuilder.Build()
			for _, artifact := range task.Artifacts {
				if err := getter.GetArtifact(taskEnv, artifact, r.taskDir.Dir); err != nil {
					wrapped := fmt.Errorf("failed to download artifact %q: %v", artifact.GetterSource, err)
					r.logger.Printf("[DEBUG] client: %v", wrapped)
					r.setState(structs.TaskStatePending,
						structs.NewTaskEvent(structs.TaskArtifactDownloadFailed).SetDownloadError(wrapped))
					r.restartTracker.SetStartError(structs.WrapRecoverable(wrapped.Error(), err))
					goto RESTART
				}
			}

			r.persistLock.Lock()
			r.artifactsDownloaded = true
			r.persistLock.Unlock()
		}

		// We don't have to wait for any template
		if len(task.Templates) == 0 {
			// Send the start signal
			select {
			case r.startCh <- struct{}{}:
			default:
			}

			resultCh <- true
			return
		}

		// Build the template manager
		if r.templateManager == nil {
			var err error
			r.templateManager, err = NewTaskTemplateManager(r, task.Templates,
				r.config, r.vaultFuture.Get(), r.taskDir.Dir, r.envBuilder)
			if err != nil {
				err := fmt.Errorf("failed to build task's template manager: %v", err)
				r.setState(structs.TaskStateDead, structs.NewTaskEvent(structs.TaskSetupFailure).SetSetupError(err).SetFailsTask())
				r.logger.Printf("[ERR] client: alloc %q, task %q %v", alloc.ID, task.Name, err)
				resultCh <- false
				return
			}
		}

		// Block for consul-template
		// TODO Hooks should register themselves as blocking and then we can
		// perioidcally enumerate what we are still blocked on
		select {
		case <-r.unblockCh:
			// Send the start signal
			select {
			case r.startCh <- struct{}{}:
			default:
			}

			resultCh <- true
			return
		case <-r.waitCh:
			// The run loop has exited so exit too
			resultCh <- false
			return
		}

	RESTART:
		restart := r.shouldRestart()
		if !restart {
			resultCh <- false
			return
		}
	}
}

// postrun is used to do any cleanup that is necessary after exiting the runloop
func (r *TaskRunner) postrun() {
	// Stop the template manager
	if r.templateManager != nil {
		r.templateManager.Stop()
	}
}

// run is the main run loop that handles starting the application, destroying
// it, restarts and signals.
func (r *TaskRunner) run() {
	// Predeclare things so we can jump to the RESTART
	var stopCollection chan struct{}
	var handleWaitCh chan *dstructs.WaitResult

	// If we already have a handle, populate the stopCollection and handleWaitCh
	// to fix the invariant that it exists.
	handleEmpty := r.getHandle() == nil

	if !handleEmpty {
		stopCollection = make(chan struct{})
		go r.collectResourceUsageStats(stopCollection)
		handleWaitCh = r.handle.WaitCh()
	}

	for {
		// Do the prestart activities
		prestartResultCh := make(chan bool, 1)
		go r.prestart(r.alloc, r.task, prestartResultCh)

	WAIT:
		for {
			select {
			case success := <-prestartResultCh:
				if !success {
					r.cleanup()
					r.setState(structs.TaskStateDead, nil)
					return
				}
			case <-r.startCh:
				// Start the task if not yet started or it is being forced. This logic
				// is necessary because in the case of a restore the handle already
				// exists.
				handleEmpty := r.getHandle() == nil
				if handleEmpty {
					startErr := r.startTask()
					r.restartTracker.SetStartError(startErr)
					if startErr != nil {
						r.setState("", structs.NewTaskEvent(structs.TaskDriverFailure).SetDriverError(startErr))
						goto RESTART
					}

					// Mark the task as started
					r.setState(structs.TaskStateRunning, structs.NewTaskEvent(structs.TaskStarted))
					r.runningLock.Lock()
					r.running = true
					r.runningLock.Unlock()

					if stopCollection == nil {
						stopCollection = make(chan struct{})
						go r.collectResourceUsageStats(stopCollection)
					}

					handleWaitCh = r.handle.WaitCh()
				}

			case waitRes := <-handleWaitCh:
				if waitRes == nil {
					panic("nil wait")
				}

				r.runningLock.Lock()
				r.running = false
				r.runningLock.Unlock()

				// Stop collection of the task's resource usage
				close(stopCollection)

				// Log whether the task was successful or not.
				r.restartTracker.SetWaitResult(waitRes)
				r.setState("", r.waitErrorToEvent(waitRes))
				if !waitRes.Successful() {
					r.logger.Printf("[INFO] client: task %q for alloc %q failed: %v", r.task.Name, r.alloc.ID, waitRes)
				} else {
					r.logger.Printf("[INFO] client: task %q for alloc %q completed successfully", r.task.Name, r.alloc.ID)
				}

				break WAIT
			case update := <-r.updateCh:
				if err := r.handleUpdate(update); err != nil {
					r.logger.Printf("[ERR] client: update to task %q failed: %v", r.task.Name, err)
				}

			case se := <-r.signalCh:
				r.runningLock.Lock()
				running := r.running
				r.runningLock.Unlock()
				common := fmt.Sprintf("signal %v to task %v for alloc %q", se.s, r.task.Name, r.alloc.ID)
				if !running {
					// Send no error
					r.logger.Printf("[DEBUG] client: skipping %s", common)
					se.result <- nil
					continue
				}

				r.logger.Printf("[DEBUG] client: sending %s", common)
				r.setState(structs.TaskStateRunning, se.e)

				res := r.handle.Signal(se.s)
				se.result <- res

			case event := <-r.restartCh:
				r.runningLock.Lock()
				running := r.running
				r.runningLock.Unlock()
				common := fmt.Sprintf("task %v for alloc %q", r.task.Name, r.alloc.ID)
				if !running {
					r.logger.Printf("[DEBUG] client: skipping restart of %v: task isn't running", common)
					continue
				}

				r.logger.Printf("[DEBUG] client: restarting %s: %v", common, event.RestartReason)
				r.setState(structs.TaskStateRunning, event)
				r.killTask(nil)

				close(stopCollection)

				if handleWaitCh != nil {
					<-handleWaitCh
				}

				// Since the restart isn't from a failure, restart immediately
				// and don't count against the restart policy
				r.restartTracker.SetRestartTriggered()
				break WAIT

			case <-r.destroyCh:
				r.runningLock.Lock()
				running := r.running
				r.runningLock.Unlock()
				if !running {
					r.cleanup()
					r.setState(structs.TaskStateDead, r.destroyEvent)
					return
				}

				// Remove from consul before killing the task so that traffic
				// can be rerouted
				interpTask := interpolateServices(r.envBuilder.Build(), r.task)
				r.consul.RemoveTask(r.alloc.ID, interpTask)

				// Store the task event that provides context on the task
				// destroy. The Killed event is set from the alloc_runner and
				// doesn't add detail
				var killEvent *structs.TaskEvent
				if r.destroyEvent.Type != structs.TaskKilled {
					if r.destroyEvent.Type == structs.TaskKilling {
						killEvent = r.destroyEvent
					} else {
						r.setState(structs.TaskStateRunning, r.destroyEvent)
					}
				}

				r.killTask(killEvent)
				close(stopCollection)

				// Wait for handler to exit before calling cleanup
				<-handleWaitCh
				r.cleanup()

				r.setState(structs.TaskStateDead, nil)
				return
			}
		}

	RESTART:
		// shouldRestart will block if the task should restart after a delay.
		restart := r.shouldRestart()
		if !restart {
			r.cleanup()
			r.setState(structs.TaskStateDead, nil)
			return
		}

		// Clear the handle so a new driver will be created.
		r.handleLock.Lock()
		r.handle = nil
		handleWaitCh = nil
		stopCollection = nil
		r.handleLock.Unlock()
	}
}

// cleanup removes Consul entries and calls Driver.Cleanup when a task is
// stopping. Errors are logged.
func (r *TaskRunner) cleanup() {
	// Remove from Consul
	interpTask := interpolateServices(r.envBuilder.Build(), r.task)
	r.consul.RemoveTask(r.alloc.ID, interpTask)

	drv, err := r.createDriver()
	if err != nil {
		r.logger.Printf("[ERR] client: error creating driver to cleanup resources: %v", err)
		return
	}

	res := r.getCreatedResources()

	ctx := driver.NewExecContext(r.taskDir, r.envBuilder.Build())
	attempts := 1
	var cleanupErr error
	for retry := true; retry; attempts++ {
		cleanupErr = drv.Cleanup(ctx, res)
		retry = structs.IsRecoverable(cleanupErr)

		// Copy current createdResources state in case SaveState is
		// called between retries
		r.setCreatedResources(res)

		// Retry 3 times with sleeps between
		if !retry || attempts > 3 {
			break
		}
		time.Sleep(time.Duration(attempts) * time.Second)
	}

	if cleanupErr != nil {
		r.logger.Printf("[ERR] client: error cleaning up resources for task %q after %d attempts: %v", r.task.Name, attempts, cleanupErr)
	}
	return
}

// shouldRestart returns if the task should restart. If the return value is
// true, the task's restart policy has already been considered and any wait time
// between restarts has been applied.
func (r *TaskRunner) shouldRestart() bool {
	state, when := r.restartTracker.GetState()
	reason := r.restartTracker.GetReason()
	switch state {
	case structs.TaskNotRestarting, structs.TaskTerminated:
		r.logger.Printf("[INFO] client: Not restarting task: %v for alloc: %v ", r.task.Name, r.alloc.ID)
		if state == structs.TaskNotRestarting {
			r.setState(structs.TaskStateDead,
				structs.NewTaskEvent(structs.TaskNotRestarting).
					SetRestartReason(reason).SetFailsTask())
		}
		return false
	case structs.TaskRestarting:
		r.logger.Printf("[INFO] client: Restarting task %q for alloc %q in %v", r.task.Name, r.alloc.ID, when)
		r.setState(structs.TaskStatePending,
			structs.NewTaskEvent(structs.TaskRestarting).
				SetRestartDelay(when).
				SetRestartReason(reason))
	default:
		r.logger.Printf("[ERR] client: restart tracker returned unknown state: %q", state)
		return false
	}

	// Unregister from Consul while waiting to restart.
	interpTask := interpolateServices(r.envBuilder.Build(), r.task)
	r.consul.RemoveTask(r.alloc.ID, interpTask)

	// Sleep but watch for destroy events.
	select {
	case <-time.After(when):
	case <-r.destroyCh:
	}

	// Destroyed while we were waiting to restart, so abort.
	r.destroyLock.Lock()
	destroyed := r.destroy
	r.destroyLock.Unlock()
	if destroyed {
		r.logger.Printf("[DEBUG] client: Not restarting task: %v because it has been destroyed", r.task.Name)
		r.setState(structs.TaskStateDead, r.destroyEvent)
		return false
	}

	return true
}

// killTask kills the running task. A killing event can optionally be passed and
// this event is used to mark the task as being killed. It provides a means to
// store extra information.
func (r *TaskRunner) killTask(killingEvent *structs.TaskEvent) {
	r.runningLock.Lock()
	running := r.running
	r.runningLock.Unlock()
	if !running {
		return
	}

	// Get the kill timeout
	timeout := driver.GetKillTimeout(r.task.KillTimeout, r.config.MaxKillTimeout)

	// Build the event
	var event *structs.TaskEvent
	if killingEvent != nil {
		event = killingEvent
		event.Type = structs.TaskKilling
	} else {
		event = structs.NewTaskEvent(structs.TaskKilling)
	}
	event.SetKillTimeout(timeout)

	// Mark that we received the kill event
	r.setState(structs.TaskStateRunning, event)

	handle := r.getHandle()

	// Kill the task using an exponential backoff in-case of failures.
	destroySuccess, err := r.handleDestroy(handle)
	if !destroySuccess {
		// We couldn't successfully destroy the resource created.
		r.logger.Printf("[ERR] client: failed to kill task %q. Resources may have been leaked: %v", r.task.Name, err)
	}

	r.runningLock.Lock()
	r.running = false
	r.runningLock.Unlock()

	// Store that the task has been destroyed and any associated error.
	r.setState("", structs.NewTaskEvent(structs.TaskKilled).SetKillError(err))
}

// startTask creates the driver, task dir, and starts the task.
func (r *TaskRunner) startTask() error {
	// Create a driver
	drv, err := r.createDriver()
	if err != nil {
		return fmt.Errorf("failed to create driver of task %q for alloc %q: %v",
			r.task.Name, r.alloc.ID, err)
	}

	// Run prestart
	ctx := driver.NewExecContext(r.taskDir, r.envBuilder.Build())
	presp, err := drv.Prestart(ctx, r.task)

	// Merge newly created resources into previously created resources
	if presp != nil {
		r.createdResourcesLock.Lock()
		r.createdResources.Merge(presp.CreatedResources)
		r.createdResourcesLock.Unlock()

		// Set any network configuration returned by the driver
		r.envBuilder.SetDriverNetwork(presp.Network)
	}

	if err != nil {
		wrapped := fmt.Sprintf("failed to initialize task %q for alloc %q: %v",
			r.task.Name, r.alloc.ID, err)
		r.logger.Printf("[WARN] client: error from prestart: %s", wrapped)
		return structs.WrapRecoverable(wrapped, err)
	}

	// Create a new context for Start since the environment may have been updated.
	ctx = driver.NewExecContext(r.taskDir, r.envBuilder.Build())

	// Start the job
	sresp, err := drv.Start(ctx, r.task)
	if err != nil {
		wrapped := fmt.Sprintf("failed to start task %q for alloc %q: %v",
			r.task.Name, r.alloc.ID, err)
		r.logger.Printf("[WARN] client: %s", wrapped)
		return structs.WrapRecoverable(wrapped, err)

	}

	// Update environment with the network defined by the driver's Start method.
	r.envBuilder.SetDriverNetwork(sresp.Network)

	if err := r.registerServices(drv, sresp.Handle, sresp.Network); err != nil {
		// All IO is done asynchronously, so errors from registering
		// services are hard failures.
		r.logger.Printf("[ERR] client: failed to register services and checks for task %q alloc %q: %v", r.task.Name, r.alloc.ID, err)

		// Kill the started task
		if destroyed, err := r.handleDestroy(sresp.Handle); !destroyed {
			r.logger.Printf("[ERR] client: failed to kill task %q alloc %q. Resources may be leaked: %v",
				r.task.Name, r.alloc.ID, err)
		}
		return structs.NewRecoverableError(err, false)
	}

	r.handleLock.Lock()
	r.handle = sresp.Handle
	r.handleLock.Unlock()

	// Need to persist the driver network between restarts
	r.driverNetLock.Lock()
	r.driverNet = sresp.Network
	r.driverNetLock.Unlock()

	return nil
}

// registerServices and checks with Consul.
func (r *TaskRunner) registerServices(d driver.Driver, h driver.DriverHandle, n *cstructs.DriverNetwork) error {
	var exec driver.ScriptExecutor
	if d.Abilities().Exec {
		// Allow set the script executor if the driver supports it
		exec = h
	}
	interpolatedTask := interpolateServices(r.envBuilder.Build(), r.task)
	return r.consul.RegisterTask(r.alloc.ID, interpolatedTask, exec, n)
}

// interpolateServices interpolates tags in a service and checks with values from the
// task's environment.
func interpolateServices(taskEnv *env.TaskEnv, task *structs.Task) *structs.Task {
	taskCopy := task.Copy()
	for _, service := range taskCopy.Services {
		for _, check := range service.Checks {
			check.Name = taskEnv.ReplaceEnv(check.Name)
			check.Type = taskEnv.ReplaceEnv(check.Type)
			check.Command = taskEnv.ReplaceEnv(check.Command)
			check.Args = taskEnv.ParseAndReplace(check.Args)
			check.Path = taskEnv.ReplaceEnv(check.Path)
			check.Protocol = taskEnv.ReplaceEnv(check.Protocol)
			check.PortLabel = taskEnv.ReplaceEnv(check.PortLabel)
			check.InitialStatus = taskEnv.ReplaceEnv(check.InitialStatus)
		}
		service.Name = taskEnv.ReplaceEnv(service.Name)
		service.PortLabel = taskEnv.ReplaceEnv(service.PortLabel)
		service.Tags = taskEnv.ParseAndReplace(service.Tags)
	}
	return taskCopy
}

// buildTaskDir creates the task directory before driver.Prestart. It is safe
// to call multiple times as its state is persisted.
func (r *TaskRunner) buildTaskDir(fsi cstructs.FSIsolation) error {
	r.persistLock.Lock()
	built := r.taskDirBuilt
	r.persistLock.Unlock()

	// We do not set the state again since this only occurs during restoration
	// and the task dir is already built. The reason we call Build again is to
	// ensure that the task dir invariants are still held.
	if !built {
		r.setState(structs.TaskStatePending, structs.NewTaskEvent(structs.TaskSetup).
			SetMessage(structs.TaskBuildingTaskDir))
	}

	chroot := config.DefaultChrootEnv
	if len(r.config.ChrootEnv) > 0 {
		chroot = r.config.ChrootEnv
	}
	if err := r.taskDir.Build(built, chroot, fsi); err != nil {
		return err
	}

	// Mark task dir as successfully built
	r.persistLock.Lock()
	r.taskDirBuilt = true
	r.persistLock.Unlock()

	// Set path and host related env vars
	driver.SetEnvvars(r.envBuilder, fsi, r.taskDir, r.config)
	return nil
}

// collectResourceUsageStats starts collecting resource usage stats of a Task.
// Collection ends when the passed channel is closed
func (r *TaskRunner) collectResourceUsageStats(stopCollection <-chan struct{}) {
	// start collecting the stats right away and then start collecting every
	// collection interval
	next := time.NewTimer(0)
	defer next.Stop()
	for {
		select {
		case <-next.C:
			next.Reset(r.config.StatsCollectionInterval)
			handle := r.getHandle()
			if handle == nil {
				continue
			}
			ru, err := handle.Stats()

			if err != nil {
				// Check if the driver doesn't implement stats
				if err.Error() == driver.DriverStatsNotImplemented.Error() {
					r.logger.Printf("[DEBUG] client: driver for task %q in allocation %q doesn't support stats", r.task.Name, r.alloc.ID)
					return
				}

				// We do not log when the plugin is shutdown as this is simply a
				// race between the stopCollection channel being closed and calling
				// Stats on the handle.
				if !strings.Contains(err.Error(), "connection is shut down") {
					r.logger.Printf("[WARN] client: error fetching stats of task %v: %v", r.task.Name, err)
				}
				continue
			}

			r.resourceUsageLock.Lock()
			r.resourceUsage = ru
			r.resourceUsageLock.Unlock()
			if ru != nil {
				r.emitStats(ru)
			}
		case <-stopCollection:
			return
		}
	}
}

// LatestResourceUsage returns the last resource utilization datapoint collected
func (r *TaskRunner) LatestResourceUsage() *cstructs.TaskResourceUsage {
	r.resourceUsageLock.RLock()
	defer r.resourceUsageLock.RUnlock()
	r.runningLock.Lock()
	defer r.runningLock.Unlock()

	// If the task is not running there can be no latest resource
	if !r.running {
		return nil
	}

	return r.resourceUsage
}

// handleUpdate takes an updated allocation and updates internal state to
// reflect the new config for the task.
func (r *TaskRunner) handleUpdate(update *structs.Allocation) error {
	// Extract the task group from the alloc.
	tg := update.Job.LookupTaskGroup(update.TaskGroup)
	if tg == nil {
		return fmt.Errorf("alloc '%s' missing task group '%s'", update.ID, update.TaskGroup)
	}

	// Extract the task.
	var updatedTask *structs.Task
	for _, t := range tg.Tasks {
		if t.Name == r.task.Name {
			updatedTask = t.Copy()
		}
	}
	if updatedTask == nil {
		return fmt.Errorf("task group %q doesn't contain task %q", tg.Name, r.task.Name)
	}

	// Merge in the task resources
	updatedTask.Resources = update.TaskResources[updatedTask.Name]

	// Update the task's environment for interpolating in services/checks
	r.envBuilder.UpdateTask(update, updatedTask)

	var mErr multierror.Error
	r.handleLock.Lock()
	if r.handle != nil {
		drv, err := r.createDriver()
		if err != nil {
			// Something has really gone wrong; don't continue
			r.handleLock.Unlock()
			return fmt.Errorf("error accessing driver when updating task %q: %v", r.task.Name, err)
		}

		// Update will update resources and store the new kill timeout.
		if err := r.handle.Update(updatedTask); err != nil {
			mErr.Errors = append(mErr.Errors, fmt.Errorf("updating task resources failed: %v", err))
		}

		// Update services in Consul
		if err := r.updateServices(drv, r.handle, r.task, updatedTask); err != nil {
			mErr.Errors = append(mErr.Errors, fmt.Errorf("error updating services and checks in Consul: %v", err))
		}
	}
	r.handleLock.Unlock()

	// Update the restart policy.
	if r.restartTracker != nil {
		r.restartTracker.SetPolicy(tg.RestartPolicy)
	}

	// Store the updated alloc.
	r.alloc = update
	r.task = updatedTask
	return mErr.ErrorOrNil()
}

// updateServices and checks with Consul.
func (r *TaskRunner) updateServices(d driver.Driver, h driver.ScriptExecutor, old, new *structs.Task) error {
	var exec driver.ScriptExecutor
	if d.Abilities().Exec {
		// Allow set the script executor if the driver supports it
		exec = h
	}
	newInterpolatedTask := interpolateServices(r.envBuilder.Build(), new)
	oldInterpolatedTask := interpolateServices(r.envBuilder.Build(), old)
	r.driverNetLock.Lock()
	net := r.driverNet.Copy()
	r.driverNetLock.Unlock()
	return r.consul.UpdateTask(r.alloc.ID, oldInterpolatedTask, newInterpolatedTask, exec, net)
}

// handleDestroy kills the task handle. In the case that killing fails,
// handleDestroy will retry with an exponential backoff and will give up at a
// given limit. It returns whether the task was destroyed and the error
// associated with the last kill attempt.
func (r *TaskRunner) handleDestroy(handle driver.DriverHandle) (destroyed bool, err error) {
	// Cap the number of times we attempt to kill the task.
	for i := 0; i < killFailureLimit; i++ {
		if err = handle.Kill(); err != nil {
			// Calculate the new backoff
			backoff := (1 << (2 * uint64(i))) * killBackoffBaseline
			if backoff > killBackoffLimit {
				backoff = killBackoffLimit
			}

			r.logger.Printf("[ERR] client: failed to kill task '%s' for alloc %q. Retrying in %v: %v",
				r.task.Name, r.alloc.ID, backoff, err)
			time.Sleep(time.Duration(backoff))
		} else {
			// Kill was successful
			return true, nil
		}
	}
	return
}

// Restart will restart the task
func (r *TaskRunner) Restart(source, reason string) {
	reasonStr := fmt.Sprintf("%s: %s", source, reason)
	event := structs.NewTaskEvent(structs.TaskRestartSignal).SetRestartReason(reasonStr)

	select {
	case r.restartCh <- event:
	case <-r.waitCh:
	}
}

// Signal will send a signal to the task
func (r *TaskRunner) Signal(source, reason string, s os.Signal) error {

	reasonStr := fmt.Sprintf("%s: %s", source, reason)
	event := structs.NewTaskEvent(structs.TaskSignaling).SetTaskSignal(s).SetTaskSignalReason(reasonStr)

	resCh := make(chan error)
	se := SignalEvent{
		s:      s,
		e:      event,
		result: resCh,
	}

	select {
	case r.signalCh <- se:
	case <-r.waitCh:
	}

	return <-resCh
}

// Kill will kill a task and store the error, no longer restarting the task. If
// fail is set, the task is marked as having failed.
func (r *TaskRunner) Kill(source, reason string, fail bool) {
	reasonStr := fmt.Sprintf("%s: %s", source, reason)
	event := structs.NewTaskEvent(structs.TaskKilling).SetKillReason(reasonStr)
	if fail {
		event.SetFailsTask()
	}

	r.logger.Printf("[DEBUG] client: killing task %v for alloc %q: %v", r.task.Name, r.alloc.ID, reasonStr)
	r.Destroy(event)
}

// UnblockStart unblocks the starting of the task. It currently assumes only
// consul-template will unblock
func (r *TaskRunner) UnblockStart(source string) {
	r.unblockLock.Lock()
	defer r.unblockLock.Unlock()
	if r.unblocked {
		return
	}

	r.logger.Printf("[DEBUG] client: unblocking task %v for alloc %q: %v", r.task.Name, r.alloc.ID, source)
	r.unblocked = true
	close(r.unblockCh)
}

// Helper function for converting a WaitResult into a TaskTerminated event.
func (r *TaskRunner) waitErrorToEvent(res *dstructs.WaitResult) *structs.TaskEvent {
	return structs.NewTaskEvent(structs.TaskTerminated).
		SetExitCode(res.ExitCode).
		SetSignal(res.Signal).
		SetExitMessage(res.Err)
}

// Update is used to update the task of the context
func (r *TaskRunner) Update(update *structs.Allocation) {
	select {
	case r.updateCh <- update:
	default:
		r.logger.Printf("[ERR] client: dropping task update '%s' (alloc '%s')",
			r.task.Name, r.alloc.ID)
	}
}

// Destroy is used to indicate that the task context should be destroyed. The
// event parameter provides a context for the destroy.
func (r *TaskRunner) Destroy(event *structs.TaskEvent) {
	r.destroyLock.Lock()
	defer r.destroyLock.Unlock()

	if r.destroy {
		return
	}
	r.destroy = true
	r.destroyEvent = event
	close(r.destroyCh)
}

// getCreatedResources returns the resources created by drivers. It will never
// return nil.
func (r *TaskRunner) getCreatedResources() *driver.CreatedResources {
	r.createdResourcesLock.Lock()
	if r.createdResources == nil {
		r.createdResources = driver.NewCreatedResources()
	}
	cr := r.createdResources.Copy()
	r.createdResourcesLock.Unlock()

	return cr
}

// setCreatedResources updates the resources created by drivers. If passed nil
// it will set createdResources to an initialized struct.
func (r *TaskRunner) setCreatedResources(cr *driver.CreatedResources) {
	if cr == nil {
		cr = driver.NewCreatedResources()
	}
	r.createdResourcesLock.Lock()
	r.createdResources = cr.Copy()
	r.createdResourcesLock.Unlock()
}

// emitStats emits resource usage stats of tasks to remote metrics collector
// sinks
func (r *TaskRunner) emitStats(ru *cstructs.TaskResourceUsage) {
	if ru.ResourceUsage.MemoryStats != nil && r.config.PublishAllocationMetrics {
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "memory", "rss"}, float32(ru.ResourceUsage.MemoryStats.RSS))
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "memory", "cache"}, float32(ru.ResourceUsage.MemoryStats.Cache))
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "memory", "swap"}, float32(ru.ResourceUsage.MemoryStats.Swap))
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "memory", "max_usage"}, float32(ru.ResourceUsage.MemoryStats.MaxUsage))
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "memory", "kernel_usage"}, float32(ru.ResourceUsage.MemoryStats.KernelUsage))
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "memory", "kernel_max_usage"}, float32(ru.ResourceUsage.MemoryStats.KernelMaxUsage))
	}

	if ru.ResourceUsage.CpuStats != nil && r.config.PublishAllocationMetrics {
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "cpu", "total_percent"}, float32(ru.ResourceUsage.CpuStats.Percent))
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "cpu", "system"}, float32(ru.ResourceUsage.CpuStats.SystemMode))
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "cpu", "user"}, float32(ru.ResourceUsage.CpuStats.UserMode))
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "cpu", "throttled_time"}, float32(ru.ResourceUsage.CpuStats.ThrottledTime))
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "cpu", "throttled_periods"}, float32(ru.ResourceUsage.CpuStats.ThrottledPeriods))
		metrics.SetGauge([]string{"client", "allocs", r.alloc.Job.Name, r.alloc.TaskGroup, r.alloc.ID, r.task.Name, "cpu", "total_ticks"}, float32(ru.ResourceUsage.CpuStats.TotalTicks))
	}
}