Merge branch 'builder-amazon-ebs-chroot'

This adds "no-launch" EBS-backed AMI creation, which allows the creation
of these AMIs without launching a new EC2 instance. Instead this builder
is meant to be run on an existing EC2 instance and uses that instance as
a host to attach root EBS volumes, provision in a chroot, etc.

builder/amazon/chroot/builder.go

@@ -0,0 +1,199 @@
+// The chroot package is able to create an Amazon AMI without requiring
+// the launch of a new instance for every build. It does this by attaching
+// and mounting the root volume of another AMI and chrooting into that
+// directory. It then creates an AMI from that attached drive.
+package chroot
+
+import (
+	"errors"
+	"fmt"
+	"github.com/mitchellh/goamz/ec2"
+	"github.com/mitchellh/multistep"
+	awscommon "github.com/mitchellh/packer/builder/amazon/common"
+	"github.com/mitchellh/packer/builder/common"
+	"github.com/mitchellh/packer/packer"
+	"log"
+	"runtime"
+	"text/template"
+)
+
+// The unique ID for this builder
+const BuilderId = "mitchellh.amazon.chroot"
+
+// Config is the configuration that is chained through the steps and
+// settable from the template.
+type Config struct {
+	common.PackerConfig    `mapstructure:",squash"`
+	awscommon.AccessConfig `mapstructure:",squash"`
+
+	AMIName        string     `mapstructure:"ami_name"`
+	ChrootMounts   [][]string `mapstructure:"chroot_mounts"`
+	CopyFiles      []string   `mapstructure:"copy_files"`
+	DevicePath     string     `mapstructure:"device_path"`
+	MountCommand   string     `mapstructure:"mount_command"`
+	MountPath      string     `mapstructure:"mount_path"`
+	SourceAmi      string     `mapstructure:"source_ami"`
+	UnmountCommand string     `mapstructure:"unmount_command"`
+}
+
+type Builder struct {
+	config Config
+	runner multistep.Runner
+}
+
+func (b *Builder) Prepare(raws ...interface{}) error {
+	md, err := common.DecodeConfig(&b.config, raws...)
+	if err != nil {
+		return err
+	}
+
+	// Defaults
+	if b.config.ChrootMounts == nil {
+		b.config.ChrootMounts = make([][]string, 0)
+	}
+
+	if b.config.CopyFiles == nil {
+		b.config.CopyFiles = make([]string, 0)
+	}
+
+	if len(b.config.ChrootMounts) == 0 {
+		b.config.ChrootMounts = [][]string{
+			[]string{"proc", "proc", "/proc"},
+			[]string{"sysfs", "sysfs", "/sys"},
+			[]string{"bind", "/dev", "/dev"},
+			[]string{"devpts", "devpts", "/dev/pts"},
+			[]string{"binfmt_misc", "binfmt_misc", "/proc/sys/fs/binfmt_misc"},
+		}
+	}
+
+	if len(b.config.CopyFiles) == 0 {
+		b.config.CopyFiles = []string{"/etc/resolv.conf"}
+	}
+
+	if b.config.MountCommand == "" {
+		b.config.MountCommand = "mount"
+	}
+
+	if b.config.MountPath == "" {
+		b.config.MountPath = "packer-amazon-chroot-volumes/{{.Device}}"
+	}
+
+	if b.config.UnmountCommand == "" {
+		b.config.UnmountCommand = "umount"
+	}
+
+	// Accumulate any errors
+	errs := common.CheckUnusedConfig(md)
+	errs = packer.MultiErrorAppend(errs, b.config.AccessConfig.Prepare()...)
+
+	if b.config.AMIName == "" {
+		errs = packer.MultiErrorAppend(
+			errs, errors.New("ami_name must be specified"))
+	} else {
+		_, err = template.New("ami").Parse(b.config.AMIName)
+		if err != nil {
+			errs = packer.MultiErrorAppend(
+				errs, fmt.Errorf("Failed parsing ami_name: %s", err))
+		}
+	}
+
+	for _, mounts := range b.config.ChrootMounts {
+		if len(mounts) != 3 {
+			errs = packer.MultiErrorAppend(
+				errs, errors.New("Each chroot_mounts entry should be three elements."))
+			break
+		}
+	}
+
+	if b.config.SourceAmi == "" {
+		errs = packer.MultiErrorAppend(errs, errors.New("source_ami is required."))
+	}
+
+	if errs != nil && len(errs.Errors) > 0 {
+		return errs
+	}
+
+	log.Printf("Config: %+v", b.config)
+	return nil
+}
+
+func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packer.Artifact, error) {
+	if runtime.GOOS != "linux" {
+		return nil, errors.New("The amazon-chroot builder only works on Linux environments.")
+	}
+
+	region, err := b.config.Region()
+	if err != nil {
+		return nil, err
+	}
+
+	auth, err := b.config.AccessConfig.Auth()
+	if err != nil {
+		return nil, err
+	}
+
+	ec2conn := ec2.New(auth, region)
+
+	// Setup the state bag and initial state for the steps
+	state := make(map[string]interface{})
+	state["config"] = &b.config
+	state["ec2"] = ec2conn
+	state["hook"] = hook
+	state["ui"] = ui
+
+	// Build the steps
+	steps := []multistep.Step{
+		&StepInstanceInfo{},
+		&StepSourceAMIInfo{},
+		&StepFlock{},
+		&StepPrepareDevice{},
+		&StepCreateVolume{},
+		&StepAttachVolume{},
+		&StepEarlyUnflock{},
+		&StepMountDevice{},
+		&StepMountExtra{},
+		&StepCopyFiles{},
+		&StepChrootProvision{},
+		&StepEarlyCleanup{},
+		&StepSnapshot{},
+		&StepRegisterAMI{},
+	}
+
+	// Run!
+	if b.config.PackerDebug {
+		b.runner = &multistep.DebugRunner{
+			Steps:   steps,
+			PauseFn: common.MultistepDebugFn(ui),
+		}
+	} else {
+		b.runner = &multistep.BasicRunner{Steps: steps}
+	}
+
+	b.runner.Run(state)
+
+	// If there was an error, return that
+	if rawErr, ok := state["error"]; ok {
+		return nil, rawErr.(error)
+	}
+
+	// If there are no AMIs, then just return
+	if _, ok := state["amis"]; !ok {
+		return nil, nil
+	}
+
+	// Build the artifact and return it
+	artifact := &awscommon.Artifact{
+		Amis:           state["amis"].(map[string]string),
+		BuilderIdValue: BuilderId,
+		Conn:           ec2conn,
+	}
+
+	return artifact, nil
+}
+
+func (b *Builder) Cancel() {
+	if b.runner != nil {
+		log.Println("Cancelling the step runner...")
+		b.runner.Cancel()
+	}
+}

builder/amazon/chroot/builder_test.go

@@ -0,0 +1,84 @@
+package chroot
+
+import (
+	"github.com/mitchellh/packer/packer"
+	"testing"
+)
+
+func testConfig() map[string]interface{} {
+	return map[string]interface{}{
+		"ami_name":   "foo",
+		"source_ami": "foo",
+	}
+}
+
+func TestBuilder_ImplementsBuilder(t *testing.T) {
+	var raw interface{}
+	raw = &Builder{}
+	if _, ok := raw.(packer.Builder); !ok {
+		t.Fatalf("Builder should be a builder")
+	}
+}
+
+func TestBuilderPrepare_AMIName(t *testing.T) {
+	var b Builder
+	config := testConfig()
+
+	// Test good
+	config["ami_name"] = "foo"
+	err := b.Prepare(config)
+	if err != nil {
+		t.Fatalf("should not have error: %s", err)
+	}
+
+	// Test bad
+	config["ami_name"] = "foo {{"
+	b = Builder{}
+	err = b.Prepare(config)
+	if err == nil {
+		t.Fatal("should have error")
+	}
+
+	// Test bad
+	delete(config, "ami_name")
+	b = Builder{}
+	err = b.Prepare(config)
+	if err == nil {
+		t.Fatal("should have error")
+	}
+}
+
+func TestBuilderPrepare_ChrootMounts(t *testing.T) {
+	b := &Builder{}
+	config := testConfig()
+
+	config["chroot_mounts"] = nil
+	err := b.Prepare(config)
+	if err != nil {
+		t.Errorf("err: %s", err)
+	}
+
+	config["chroot_mounts"] = [][]string{
+		[]string{"bad"},
+	}
+	err = b.Prepare(config)
+	if err == nil {
+		t.Fatal("should have error")
+	}
+}
+func TestBuilderPrepare_SourceAmi(t *testing.T) {
+	b := &Builder{}
+	config := testConfig()
+
+	config["source_ami"] = ""
+	err := b.Prepare(config)
+	if err == nil {
+		t.Fatal("should have error")
+	}
+
+	config["source_ami"] = "foo"
+	err = b.Prepare(config)
+	if err != nil {
+		t.Errorf("err: %s", err)
+	}
+}

builder/amazon/chroot/cleanup.go

@@ -0,0 +1,6 @@
+package chroot
+
+// Cleanup is an interface that some steps implement for early cleanup.
+type Cleanup interface {
+	CleanupFunc(map[string]interface{}) error
+}

builder/amazon/chroot/communicator.go

@@ -0,0 +1,87 @@
+package chroot
+
+import (
+	"github.com/mitchellh/packer/packer"
+	"io"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"syscall"
+)
+
+// Communicator is a special communicator that works by executing
+// commands locally but within a chroot.
+type Communicator struct {
+	Chroot string
+}
+
+func (c *Communicator) Start(cmd *packer.RemoteCmd) error {
+	chrootCmdPath, err := exec.LookPath("chroot")
+	if err != nil {
+		return err
+	}
+
+	localCmd := exec.Command(chrootCmdPath, c.Chroot, "/bin/sh", "-c", cmd.Command)
+	localCmd.Stdin = cmd.Stdin
+	localCmd.Stdout = cmd.Stdout
+	localCmd.Stderr = cmd.Stderr
+	log.Printf("Executing: %s %#v", localCmd.Path, localCmd.Args)
+	if err := localCmd.Start(); err != nil {
+		return err
+	}
+
+	go func() {
+		exitStatus := 0
+		if err := localCmd.Wait(); err != nil {
+			if exitErr, ok := err.(*exec.ExitError); ok {
+				exitStatus = 1
+
+				// There is no process-independent way to get the REAL
+				// exit status so we just try to go deeper.
+				if status, ok := exitErr.Sys().(syscall.WaitStatus); ok {
+					exitStatus = status.ExitStatus()
+				}
+			}
+		}
+
+		log.Printf(
+			"Chroot executation ended with '%d': '%s'",
+			exitStatus, cmd.Command)
+		cmd.SetExited(exitStatus)
+	}()
+
+	return nil
+}
+
+func (c *Communicator) Upload(dst string, r io.Reader) error {
+	dst = filepath.Join(c.Chroot, dst)
+	log.Printf("Uploading to chroot dir: %s", dst)
+	f, err := os.Create(dst)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if _, err := io.Copy(f, r); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (c *Communicator) Download(src string, w io.Writer) error {
+	src = filepath.Join(c.Chroot, src)
+	log.Printf("Downloading from chroot dir: %s", src)
+	f, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if _, err := io.Copy(w, f); err != nil {
+		return err
+	}
+
+	return nil
+}

builder/amazon/chroot/communicator_test.go

@@ -0,0 +1,14 @@
+package chroot
+
+import (
+	"github.com/mitchellh/packer/packer"
+	"testing"
+)
+
+func TestCommunicator_ImplementsCommunicator(t *testing.T) {
+	var raw interface{}
+	raw = &Communicator{}
+	if _, ok := raw.(packer.Communicator); !ok {
+		t.Fatalf("Communicator should be a communicator")
+	}
+}

builder/amazon/chroot/device.go

@@ -0,0 +1,61 @@
+package chroot
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// AvailableDevice finds an available device and returns it. Note that
+// you should externally hold a flock or something in order to guarantee
+// that this device is available across processes.
+func AvailableDevice() (string, error) {
+	prefix, err := devicePrefix()
+	if err != nil {
+		return "", err
+	}
+
+	letters := "fghijklmnop"
+	for _, letter := range letters {
+		for i := 1; i < 16; i++ {
+			device := fmt.Sprintf("/dev/%s%c%d", prefix, letter, i)
+			if _, err := os.Stat(device); err != nil {
+				return device, nil
+			}
+		}
+	}
+
+	return "", errors.New("available device could not be found")
+}
+
+// devicePrefix returns the prefix ("sd" or "xvd" or so on) of the devices
+// on the system.
+func devicePrefix() (string, error) {
+	available := []string{"sd", "xvd"}
+
+	f, err := os.Open("/sys/block")
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	dirs, err := f.Readdirnames(-1)
+	if dirs != nil && len(dirs) > 0 {
+		for _, dir := range dirs {
+			dirBase := filepath.Base(dir)
+			for _, prefix := range available {
+				if strings.HasPrefix(dirBase, prefix) {
+					return prefix, nil
+				}
+			}
+		}
+	}
+
+	if err != nil {
+		return "", err
+	}
+
+	return "", errors.New("device prefix could not be detected")
+}

builder/amazon/chroot/lockfile.go

@@ -0,0 +1,16 @@
+// +build windows
+
+package chroot
+
+import (
+	"errors"
+	"os"
+)
+
+func lockFile(*os.File) error {
+	return errors.New("not supported on Windows")
+}
+
+func unlockFile(f *os.File) error {
+	return nil
+}

builder/amazon/chroot/lockfile_unix.go

@@ -0,0 +1,32 @@
+// +build !windows
+
+package chroot
+
+import (
+	"errors"
+	"os"
+	"syscall"
+)
+
+// See: http://linux.die.net/include/sys/file.h
+const LOCK_EX = 2
+const LOCK_NB = 4
+const LOCK_UN = 8
+
+func lockFile(f *os.File) error {
+	err := syscall.Flock(int(f.Fd()), LOCK_EX|LOCK_NB)
+	if err != nil {
+		errno, ok := err.(syscall.Errno)
+		if ok && errno == syscall.EWOULDBLOCK {
+			return errors.New("file already locked")
+		}
+
+		return err
+	}
+
+	return nil
+}
+
+func unlockFile(f *os.File) error {
+	return syscall.Flock(int(f.Fd()), LOCK_UN)
+}

builder/amazon/chroot/step_attach_volume.go

@@ -0,0 +1,129 @@
+package chroot
+
+import (
+	"errors"
+	"fmt"
+	"github.com/mitchellh/goamz/ec2"
+	"github.com/mitchellh/multistep"
+	awscommon "github.com/mitchellh/packer/builder/amazon/common"
+	"github.com/mitchellh/packer/packer"
+	"strings"
+)
+
+// StepAttachVolume attaches the previously created volume to an
+// available device location.
+//
+// Produces:
+//   device string - The location where the volume was attached.
+//   attach_cleanup CleanupFunc
+type StepAttachVolume struct {
+	attached bool
+	volumeId string
+}
+
+func (s *StepAttachVolume) Run(state map[string]interface{}) multistep.StepAction {
+	ec2conn := state["ec2"].(*ec2.EC2)
+	device := state["device"].(string)
+	instance := state["instance"].(*ec2.Instance)
+	ui := state["ui"].(packer.Ui)
+	volumeId := state["volume_id"].(string)
+
+	// For the API call, it expects "sd" prefixed devices.
+	attachVolume := strings.Replace(device, "/xvd", "/sd", 1)
+
+	ui.Say(fmt.Sprintf("Attaching the root volume to %s", attachVolume))
+	_, err := ec2conn.AttachVolume(volumeId, instance.InstanceId, attachVolume)
+	if err != nil {
+		err := fmt.Errorf("Error attaching volume: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	// Mark that we attached it so we can detach it later
+	s.attached = true
+	s.volumeId = volumeId
+
+	// Wait for the volume to become attached
+	stateChange := awscommon.StateChangeConf{
+		Conn:      ec2conn,
+		Pending:   []string{"attaching"},
+		StepState: state,
+		Target:    "attached",
+		Refresh: func() (interface{}, string, error) {
+			resp, err := ec2conn.Volumes([]string{volumeId}, ec2.NewFilter())
+			if err != nil {
+				return nil, "", err
+			}
+
+			if len(resp.Volumes[0].Attachments) == 0 {
+				return nil, "", errors.New("No attachments on volume.")
+			}
+
+			return nil, resp.Volumes[0].Attachments[0].Status, nil
+		},
+	}
+
+	_, err = awscommon.WaitForState(&stateChange)
+	if err != nil {
+		err := fmt.Errorf("Error waiting for volume: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	state["attach_cleanup"] = s
+	return multistep.ActionContinue
+}
+
+func (s *StepAttachVolume) Cleanup(state map[string]interface{}) {
+	ui := state["ui"].(packer.Ui)
+	if err := s.CleanupFunc(state); err != nil {
+		ui.Error(err.Error())
+	}
+}
+
+func (s *StepAttachVolume) CleanupFunc(state map[string]interface{}) error {
+	if !s.attached {
+		return nil
+	}
+
+	ec2conn := state["ec2"].(*ec2.EC2)
+	ui := state["ui"].(packer.Ui)
+
+	ui.Say("Detaching EBS volume...")
+	_, err := ec2conn.DetachVolume(s.volumeId)
+	if err != nil {
+		return fmt.Errorf("Error detaching EBS volume: %s", err)
+	}
+
+	s.attached = false
+
+	// Wait for the volume to detach
+	stateChange := awscommon.StateChangeConf{
+		Conn:      ec2conn,
+		Pending:   []string{"attaching", "attached", "detaching"},
+		StepState: state,
+		Target:    "detached",
+		Refresh: func() (interface{}, string, error) {
+			resp, err := ec2conn.Volumes([]string{s.volumeId}, ec2.NewFilter())
+			if err != nil {
+				return nil, "", err
+			}
+
+			state := "detached"
+			if len(resp.Volumes[0].Attachments) > 0 {
+				state = resp.Volumes[0].Attachments[0].Status
+			}
+
+			return nil, state, nil
+		},
+	}
+
+	_, err = awscommon.WaitForState(&stateChange)
+	if err != nil {
+		return fmt.Errorf("Error waiting for volume: %s", err)
+	}
+
+	return nil
+}

builder/amazon/chroot/step_attach_volume_test.go

@@ -0,0 +1,11 @@
+package chroot
+
+import "testing"
+
+func TestAttachVolumeCleanupFunc_ImplementsCleanupFunc(t *testing.T) {
+	var raw interface{}
+	raw = new(StepAttachVolume)
+	if _, ok := raw.(Cleanup); !ok {
+		t.Fatalf("cleanup func should be a CleanupFunc")
+	}
+}

builder/amazon/chroot/step_chroot_provision.go

@@ -0,0 +1,34 @@
+package chroot
+
+import (
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"log"
+)
+
+// StepChrootProvision provisions the instance within a chroot.
+type StepChrootProvision struct {
+	mounts []string
+}
+
+func (s *StepChrootProvision) Run(state map[string]interface{}) multistep.StepAction {
+	hook := state["hook"].(packer.Hook)
+	mountPath := state["mount_path"].(string)
+	ui := state["ui"].(packer.Ui)
+
+	// Create our communicator
+	comm := &Communicator{
+		Chroot: mountPath,
+	}
+
+	// Provision
+	log.Println("Running the provision hook")
+	if err := hook.Run(packer.HookProvision, ui, comm, nil); err != nil {
+		state["error"] = err
+		return multistep.ActionHalt
+	}
+
+	return multistep.ActionContinue
+}
+
+func (s *StepChrootProvision) Cleanup(state map[string]interface{}) {}

builder/amazon/chroot/step_copy_files.go

@@ -0,0 +1,107 @@
+package chroot
+
+import (
+	"fmt"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"io"
+	"log"
+	"os"
+	"path/filepath"
+)
+
+// StepCopyFiles copies some files from the host into the chroot environment.
+//
+// Produces:
+//   copy_files_cleanup CleanupFunc - A function to clean up the copied files
+//   early.
+type StepCopyFiles struct {
+	files []string
+}
+
+func (s *StepCopyFiles) Run(state map[string]interface{}) multistep.StepAction {
+	config := state["config"].(*Config)
+	mountPath := state["mount_path"].(string)
+	ui := state["ui"].(packer.Ui)
+
+	s.files = make([]string, 0, len(config.CopyFiles))
+	if len(config.CopyFiles) > 0 {
+		ui.Say("Copying files from host to chroot...")
+		for _, path := range config.CopyFiles {
+			ui.Message(path)
+			chrootPath := filepath.Join(mountPath, path)
+			log.Printf("Copying '%s' to '%s'", path, chrootPath)
+
+			if err := s.copySingle(chrootPath, path); err != nil {
+				err := fmt.Errorf("Error copying file: %s", err)
+				state["error"] = err
+				ui.Error(err.Error())
+				return multistep.ActionHalt
+			}
+
+			s.files = append(s.files, chrootPath)
+		}
+	}
+
+	state["copy_files_cleanup"] = s
+	return multistep.ActionContinue
+}
+
+func (s *StepCopyFiles) Cleanup(state map[string]interface{}) {
+	ui := state["ui"].(packer.Ui)
+	if err := s.CleanupFunc(state); err != nil {
+		ui.Error(err.Error())
+	}
+}
+
+func (s *StepCopyFiles) CleanupFunc(map[string]interface{}) error {
+	if s.files != nil {
+		for _, file := range s.files {
+			log.Printf("Removing: %s", file)
+			if err := os.Remove(file); err != nil {
+				return err
+			}
+		}
+	}
+
+	s.files = nil
+	return nil
+}
+
+func (s *StepCopyFiles) copySingle(dst, src string) error {
+	// Stat the src file so we can copy the mode later
+	srcInfo, err := os.Stat(src)
+	if err != nil {
+		return err
+	}
+
+	// Remove any existing destination file
+	if err := os.Remove(dst); err != nil {
+		return err
+	}
+
+	// Copy the files
+	srcF, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer srcF.Close()
+
+	dstF, err := os.Create(dst)
+	if err != nil {
+		return err
+	}
+	defer dstF.Close()
+
+	if _, err := io.Copy(dstF, srcF); err != nil {
+		return err
+	}
+	dstF.Close()
+
+	// Match the mode
+	if err := os.Chmod(dst, srcInfo.Mode()); err != nil {
+		return err
+	}
+
+	return nil
+}

builder/amazon/chroot/step_copy_files_test.go

@@ -0,0 +1,11 @@
+package chroot
+
+import "testing"
+
+func TestCopyFilesCleanupFunc_ImplementsCleanupFunc(t *testing.T) {
+	var raw interface{}
+	raw = new(StepCopyFiles)
+	if _, ok := raw.(Cleanup); !ok {
+		t.Fatalf("cleanup func should be a CleanupFunc")
+	}
+}

builder/amazon/chroot/step_create_volume.go

@@ -0,0 +1,107 @@
+package chroot
+
+import (
+	"fmt"
+	"github.com/mitchellh/goamz/ec2"
+	"github.com/mitchellh/multistep"
+	awscommon "github.com/mitchellh/packer/builder/amazon/common"
+	"github.com/mitchellh/packer/packer"
+	"log"
+)
+
+// StepCreateVolume creates a new volume from the snapshot of the root
+// device of the AMI.
+//
+// Produces:
+//   volume_id string - The ID of the created volume
+type StepCreateVolume struct {
+	volumeId string
+}
+
+func (s *StepCreateVolume) Run(state map[string]interface{}) multistep.StepAction {
+	ec2conn := state["ec2"].(*ec2.EC2)
+	image := state["source_image"].(*ec2.Image)
+	instance := state["instance"].(*ec2.Instance)
+	ui := state["ui"].(packer.Ui)
+
+	// Determine the root device snapshot
+	log.Printf("Searching for root device of the image (%s)", image.RootDeviceName)
+	var rootDevice *ec2.BlockDeviceMapping
+	for _, device := range image.BlockDevices {
+		if device.DeviceName == image.RootDeviceName {
+			rootDevice = &device
+			break
+		}
+	}
+
+	if rootDevice == nil {
+		err := fmt.Errorf("Couldn't find root device!")
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	ui.Say("Creating the root volume...")
+	createVolume := &ec2.CreateVolume{
+		AvailZone:  instance.AvailZone,
+		Size:       rootDevice.VolumeSize,
+		SnapshotId: rootDevice.SnapshotId,
+		VolumeType: rootDevice.VolumeType,
+		IOPS:       rootDevice.IOPS,
+	}
+	log.Printf("Create args: %#v", createVolume)
+
+	createVolumeResp, err := ec2conn.CreateVolume(createVolume)
+	if err != nil {
+		err := fmt.Errorf("Error creating root volume: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	// Set the volume ID so we remember to delete it later
+	s.volumeId = createVolumeResp.VolumeId
+	log.Printf("Volume ID: %s", s.volumeId)
+
+	// Wait for the volume to become ready
+	stateChange := awscommon.StateChangeConf{
+		Conn:      ec2conn,
+		Pending:   []string{"creating"},
+		StepState: state,
+		Target:    "available",
+		Refresh: func() (interface{}, string, error) {
+			resp, err := ec2conn.Volumes([]string{s.volumeId}, ec2.NewFilter())
+			if err != nil {
+				return nil, "", err
+			}
+
+			return nil, resp.Volumes[0].Status, nil
+		},
+	}
+
+	_, err = awscommon.WaitForState(&stateChange)
+	if err != nil {
+		err := fmt.Errorf("Error waiting for volume: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	state["volume_id"] = s.volumeId
+	return multistep.ActionContinue
+}
+
+func (s *StepCreateVolume) Cleanup(state map[string]interface{}) {
+	if s.volumeId == "" {
+		return
+	}
+
+	ec2conn := state["ec2"].(*ec2.EC2)
+	ui := state["ui"].(packer.Ui)
+
+	ui.Say("Deleting the created EBS volume...")
+	_, err := ec2conn.DeleteVolume(s.volumeId)
+	if err != nil {
+		ui.Error(fmt.Sprintf("Error deleting EBS volume: %s", err))
+	}
+}

builder/amazon/chroot/step_early_cleanup.go

@@ -0,0 +1,37 @@
+package chroot
+
+import (
+	"fmt"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"log"
+)
+
+// StepEarlyCleanup performs some of the cleanup steps early in order to
+// prepare for snapshotting and creating an AMI.
+type StepEarlyCleanup struct{}
+
+func (s *StepEarlyCleanup) Run(state map[string]interface{}) multistep.StepAction {
+	ui := state["ui"].(packer.Ui)
+	cleanupKeys := []string{
+		"copy_files_cleanup",
+		"mount_extra_cleanup",
+		"mount_device_cleanup",
+		"attach_cleanup",
+	}
+
+	for _, key := range cleanupKeys {
+		c := state[key].(Cleanup)
+		log.Printf("Running cleanup func: %s", key)
+		if err := c.CleanupFunc(state); err != nil {
+			err := fmt.Errorf("Error cleaning up: %s", err)
+			state["error"] = err
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+	}
+
+	return multistep.ActionContinue
+}
+
+func (s *StepEarlyCleanup) Cleanup(state map[string]interface{}) {}

builder/amazon/chroot/step_early_unflock.go

@@ -0,0 +1,28 @@
+package chroot
+
+import (
+	"fmt"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"log"
+)
+
+// StepEarlyUnflock unlocks the flock.
+type StepEarlyUnflock struct{}
+
+func (s *StepEarlyUnflock) Run(state map[string]interface{}) multistep.StepAction {
+	cleanup := state["flock_cleanup"].(Cleanup)
+	ui := state["ui"].(packer.Ui)
+
+	log.Println("Unlocking file lock...")
+	if err := cleanup.CleanupFunc(state); err != nil {
+		err := fmt.Errorf("Error unlocking file lock: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	return multistep.ActionContinue
+}
+
+func (s *StepEarlyUnflock) Cleanup(state map[string]interface{}) {}

builder/amazon/chroot/step_flock.go

@@ -0,0 +1,72 @@
+package chroot
+
+import (
+	"fmt"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"log"
+	"os"
+	"path/filepath"
+)
+
+// StepFlock provisions the instance within a chroot.
+//
+// Produces:
+//   flock_cleanup Cleanup - To perform early cleanup
+type StepFlock struct {
+	fh *os.File
+}
+
+func (s *StepFlock) Run(state map[string]interface{}) multistep.StepAction {
+	ui := state["ui"].(packer.Ui)
+
+	lockfile := "/var/lock/packer-chroot/lock"
+	if err := os.MkdirAll(filepath.Dir(lockfile), 0755); err != nil {
+		err := fmt.Errorf("Error creating lock: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	log.Printf("Obtaining lock: %s", lockfile)
+	f, err := os.Create(lockfile)
+	if err != nil {
+		err := fmt.Errorf("Error creating lock: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	// LOCK!
+	if err := lockFile(f); err != nil {
+		err := fmt.Errorf("Error creating lock: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	// Set the file handle, we can't close it because we need to hold
+	// the lock.
+	s.fh = f
+
+	state["flock_cleanup"] = s
+	return multistep.ActionContinue
+}
+
+func (s *StepFlock) Cleanup(state map[string]interface{}) {
+	s.CleanupFunc(state)
+}
+
+func (s *StepFlock) CleanupFunc(state map[string]interface{}) error {
+	if s.fh == nil {
+		return nil
+	}
+
+	log.Printf("Unlocking: %s", s.fh.Name())
+	if err := unlockFile(s.fh); err != nil {
+		return err
+	}
+
+	s.fh = nil
+	return nil
+}

builder/amazon/chroot/step_flock_test.go

@@ -0,0 +1,11 @@
+package chroot
+
+import "testing"
+
+func TestFlockCleanupFunc_ImplementsCleanupFunc(t *testing.T) {
+	var raw interface{}
+	raw = new(StepFlock)
+	if _, ok := raw.(Cleanup); !ok {
+		t.Fatalf("cleanup func should be a CleanupFunc")
+	}
+}

builder/amazon/chroot/step_instance_info.go

@@ -0,0 +1,57 @@
+package chroot
+
+import (
+	"fmt"
+	"github.com/mitchellh/goamz/aws"
+	"github.com/mitchellh/goamz/ec2"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"log"
+)
+
+// StepInstanceInfo verifies that this builder is running on an EC2 instance.
+type StepInstanceInfo struct{}
+
+func (s *StepInstanceInfo) Run(state map[string]interface{}) multistep.StepAction {
+	ec2conn := state["ec2"].(*ec2.EC2)
+	ui := state["ui"].(packer.Ui)
+
+	// Get our own instance ID
+	ui.Say("Gathering information about this EC2 instance...")
+	instanceIdBytes, err := aws.GetMetaData("instance-id")
+	if err != nil {
+		log.Printf("Error: %s", err)
+		err := fmt.Errorf(
+			"Error retrieving the ID of the instance Packer is running on.\n" +
+				"Please verify Packer is running on a proper AWS EC2 instance.")
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	instanceId := string(instanceIdBytes)
+	log.Printf("Instance ID: %s", instanceId)
+
+	// Query the entire instance metadata
+	instancesResp, err := ec2conn.Instances([]string{instanceId}, ec2.NewFilter())
+	if err != nil {
+		err := fmt.Errorf("Error getting instance data: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	if len(instancesResp.Reservations) == 0 {
+		err := fmt.Errorf("Error getting instance data: no instance found.")
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	instance := &instancesResp.Reservations[0].Instances[0]
+	state["instance"] = instance
+
+	return multistep.ActionContinue
+}
+
+func (s *StepInstanceInfo) Cleanup(map[string]interface{}) {}

builder/amazon/chroot/step_mount_device.go

@@ -0,0 +1,103 @@
+package chroot
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"text/template"
+)
+
+type mountPathData struct {
+	Device string
+}
+
+// StepMountDevice mounts the attached device.
+//
+// Produces:
+//   mount_path string - The location where the volume was mounted.
+//   mount_device_cleanup CleanupFunc - To perform early cleanup
+type StepMountDevice struct {
+	mountPath string
+}
+
+func (s *StepMountDevice) Run(state map[string]interface{}) multistep.StepAction {
+	config := state["config"].(*Config)
+	ui := state["ui"].(packer.Ui)
+	device := state["device"].(string)
+
+	mountPathRaw := new(bytes.Buffer)
+	t := template.Must(template.New("mountPath").Parse(config.MountPath))
+	t.Execute(mountPathRaw, &mountPathData{
+		Device: filepath.Base(device),
+	})
+
+	var err error
+	mountPath := mountPathRaw.String()
+	mountPath, err = filepath.Abs(mountPath)
+	if err != nil {
+		err := fmt.Errorf("Error preparing mount directory: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	log.Printf("Mount path: %s", mountPath)
+
+	if err := os.MkdirAll(mountPath, 0755); err != nil {
+		err := fmt.Errorf("Error creating mount directory: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	ui.Say("Mounting the root device...")
+	stderr := new(bytes.Buffer)
+	mountCommand := fmt.Sprintf("%s %s %s", config.MountCommand, device, mountPath)
+	cmd := exec.Command("/bin/sh", "-c", mountCommand)
+	cmd.Stderr = stderr
+	if err := cmd.Run(); err != nil {
+		err := fmt.Errorf(
+			"Error mounting root volume: %s\nStderr: %s", err, stderr.String())
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	// Set the mount path so we remember to unmount it later
+	s.mountPath = mountPath
+	state["mount_path"] = s.mountPath
+	state["mount_device_cleanup"] = s
+
+	return multistep.ActionContinue
+}
+
+func (s *StepMountDevice) Cleanup(state map[string]interface{}) {
+	ui := state["ui"].(packer.Ui)
+	if err := s.CleanupFunc(state); err != nil {
+		ui.Error(err.Error())
+	}
+}
+
+func (s *StepMountDevice) CleanupFunc(state map[string]interface{}) error {
+	if s.mountPath == "" {
+		return nil
+	}
+
+	config := state["config"].(*Config)
+	ui := state["ui"].(packer.Ui)
+	ui.Say("Unmounting the root device...")
+
+	unmountCommand := fmt.Sprintf("%s %s", config.UnmountCommand, s.mountPath)
+	cmd := exec.Command("/bin/sh", "-c", unmountCommand)
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("Error unmounting root device: %s", err)
+	}
+
+	s.mountPath = ""
+	return nil
+}

builder/amazon/chroot/step_mount_device_test.go

@@ -0,0 +1,11 @@
+package chroot
+
+import "testing"
+
+func TestMountDeviceCleanupFunc_ImplementsCleanupFunc(t *testing.T) {
+	var raw interface{}
+	raw = new(StepMountDevice)
+	if _, ok := raw.(Cleanup); !ok {
+		t.Fatalf("cleanup func should be a CleanupFunc")
+	}
+}

builder/amazon/chroot/step_mount_extra.go

@@ -0,0 +1,100 @@
+package chroot
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"os"
+	"os/exec"
+)
+
+// StepMountExtra mounts the attached device.
+//
+// Produces:
+//   mount_extra_cleanup CleanupFunc - To perform early cleanup
+type StepMountExtra struct {
+	mounts []string
+}
+
+func (s *StepMountExtra) Run(state map[string]interface{}) multistep.StepAction {
+	config := state["config"].(*Config)
+	mountPath := state["mount_path"].(string)
+	ui := state["ui"].(packer.Ui)
+
+	s.mounts = make([]string, 0, len(config.ChrootMounts))
+
+	ui.Say("Mounting additional paths within the chroot...")
+	for _, mountInfo := range config.ChrootMounts {
+		innerPath := mountPath + mountInfo[2]
+
+		if err := os.MkdirAll(innerPath, 0755); err != nil {
+			err := fmt.Errorf("Error creating mount directory: %s", err)
+			state["error"] = err
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+
+		flags := "-t " + mountInfo[0]
+		if mountInfo[0] == "bind" {
+			flags = "--bind"
+		}
+
+		ui.Message(fmt.Sprintf("Mounting: %s", mountInfo[2]))
+		stderr := new(bytes.Buffer)
+		mountCommand := fmt.Sprintf(
+			"%s %s %s %s",
+			config.MountCommand,
+			flags,
+			mountInfo[1],
+			innerPath)
+		cmd := exec.Command("/bin/sh", "-c", mountCommand)
+		cmd.Stderr = stderr
+		if err := cmd.Run(); err != nil {
+			err := fmt.Errorf(
+				"Error mounting: %s\nStderr: %s", err, stderr.String())
+			state["error"] = err
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+
+		s.mounts = append(s.mounts, innerPath)
+	}
+
+	state["mount_extra_cleanup"] = s
+	return multistep.ActionContinue
+}
+
+func (s *StepMountExtra) Cleanup(state map[string]interface{}) {
+	ui := state["ui"].(packer.Ui)
+
+	if err := s.CleanupFunc(state); err != nil {
+		ui.Error(err.Error())
+		return
+	}
+}
+
+func (s *StepMountExtra) CleanupFunc(state map[string]interface{}) error {
+	if s.mounts == nil {
+		return nil
+	}
+
+	config := state["config"].(*Config)
+	for len(s.mounts) > 0 {
+		var path string
+		lastIndex := len(s.mounts) - 1
+		path, s.mounts = s.mounts[lastIndex], s.mounts[:lastIndex]
+		unmountCommand := fmt.Sprintf("%s %s", config.UnmountCommand, path)
+
+		stderr := new(bytes.Buffer)
+		cmd := exec.Command("/bin/sh", "-c", unmountCommand)
+		cmd.Stderr = stderr
+		if err := cmd.Run(); err != nil {
+			return fmt.Errorf(
+				"Error unmounting device: %s\nStderr: %s", err, stderr.String())
+		}
+	}
+
+	s.mounts = nil
+	return nil
+}

builder/amazon/chroot/step_mount_extra_test.go

@@ -0,0 +1,11 @@
+package chroot
+
+import "testing"
+
+func TestMountExtraCleanupFunc_ImplementsCleanupFunc(t *testing.T) {
+	var raw interface{}
+	raw = new(StepMountExtra)
+	if _, ok := raw.(Cleanup); !ok {
+		t.Fatalf("cleanup func should be a CleanupFunc")
+	}
+}

builder/amazon/chroot/step_prepare_device.go

@@ -0,0 +1,45 @@
+package chroot
+
+import (
+	"fmt"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"log"
+	"os"
+)
+
+// StepPrepareDevice finds an available device and sets it.
+type StepPrepareDevice struct {
+	mounts []string
+}
+
+func (s *StepPrepareDevice) Run(state map[string]interface{}) multistep.StepAction {
+	config := state["config"].(*Config)
+	ui := state["ui"].(packer.Ui)
+
+	device := config.DevicePath
+	if device == "" {
+		var err error
+		log.Println("Device path not specified, searching for available device...")
+		device, err = AvailableDevice()
+		if err != nil {
+			err := fmt.Errorf("Error finding available device: %s", err)
+			state["error"] = err
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+	}
+
+	if _, err := os.Stat(device); err == nil {
+		err := fmt.Errorf("Device is in use: %s", device)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	log.Printf("Device: %s", device)
+	state["device"] = device
+	return multistep.ActionContinue
+}
+
+func (s *StepPrepareDevice) Cleanup(state map[string]interface{}) {}

builder/amazon/chroot/step_register_ami.go

@@ -0,0 +1,84 @@
+package chroot
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/mitchellh/goamz/ec2"
+	"github.com/mitchellh/multistep"
+	awscommon "github.com/mitchellh/packer/builder/amazon/common"
+	"github.com/mitchellh/packer/packer"
+	"strconv"
+	"text/template"
+	"time"
+)
+
+type amiNameData struct {
+	CreateTime string
+}
+
+// StepRegisterAMI creates the AMI.
+type StepRegisterAMI struct{}
+
+func (s *StepRegisterAMI) Run(state map[string]interface{}) multistep.StepAction {
+	config := state["config"].(*Config)
+	ec2conn := state["ec2"].(*ec2.EC2)
+	image := state["source_image"].(*ec2.Image)
+	snapshotId := state["snapshot_id"].(string)
+	ui := state["ui"].(packer.Ui)
+
+	// Parse the name of the AMI
+	amiNameBuf := new(bytes.Buffer)
+	tData := amiNameData{
+		strconv.FormatInt(time.Now().UTC().Unix(), 10),
+	}
+
+	t := template.Must(template.New("ami").Parse(config.AMIName))
+	t.Execute(amiNameBuf, tData)
+	amiName := amiNameBuf.String()
+
+	ui.Say("Registering the AMI...")
+	blockDevices := make([]ec2.BlockDeviceMapping, len(image.BlockDevices))
+	for i, device := range image.BlockDevices {
+		newDevice := device
+		if newDevice.DeviceName == image.RootDeviceName {
+			newDevice.SnapshotId = snapshotId
+		}
+
+		blockDevices[i] = newDevice
+	}
+
+	registerOpts := &ec2.RegisterImage{
+		Name:           amiName,
+		Architecture:   image.Architecture,
+		KernelId:       image.KernelId,
+		RamdiskId:      image.RamdiskId,
+		RootDeviceName: image.RootDeviceName,
+		BlockDevices:   blockDevices,
+	}
+
+	registerResp, err := ec2conn.RegisterImage(registerOpts)
+	if err != nil {
+		state["error"] = fmt.Errorf("Error registering AMI: %s", err)
+		ui.Error(state["error"].(error).Error())
+		return multistep.ActionHalt
+	}
+
+	// Set the AMI ID in the state
+	ui.Say(fmt.Sprintf("AMI: %s", registerResp.ImageId))
+	amis := make(map[string]string)
+	amis[ec2conn.Region.Name] = registerResp.ImageId
+	state["amis"] = amis
+
+	// Wait for the image to become ready
+	ui.Say("Waiting for AMI to become ready...")
+	if err := awscommon.WaitForAMI(ec2conn, registerResp.ImageId); err != nil {
+		err := fmt.Errorf("Error waiting for AMI: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	return multistep.ActionContinue
+}
+
+func (s *StepRegisterAMI) Cleanup(state map[string]interface{}) {}

builder/amazon/chroot/step_snapshot.go

@@ -0,0 +1,87 @@
+package chroot
+
+import (
+	"errors"
+	"fmt"
+	"github.com/mitchellh/goamz/ec2"
+	"github.com/mitchellh/multistep"
+	awscommon "github.com/mitchellh/packer/builder/amazon/common"
+	"github.com/mitchellh/packer/packer"
+)
+
+// StepSnapshot creates a snapshot of the created volume.
+//
+// Produces:
+//   snapshot_id string - ID of the created snapshot
+type StepSnapshot struct {
+	snapshotId string
+}
+
+func (s *StepSnapshot) Run(state map[string]interface{}) multistep.StepAction {
+	ec2conn := state["ec2"].(*ec2.EC2)
+	ui := state["ui"].(packer.Ui)
+	volumeId := state["volume_id"].(string)
+
+	ui.Say("Creating snapshot...")
+	createSnapResp, err := ec2conn.CreateSnapshot(volumeId, "")
+	if err != nil {
+		err := fmt.Errorf("Error creating snapshot: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	// Set the snapshot ID so we can delete it later
+	s.snapshotId = createSnapResp.Id
+	ui.Message(fmt.Sprintf("Snapshot ID: %s", s.snapshotId))
+
+	// Wait for the snapshot to be ready
+	stateChange := awscommon.StateChangeConf{
+		Conn:      ec2conn,
+		Pending:   []string{"pending"},
+		StepState: state,
+		Target:    "completed",
+		Refresh: func() (interface{}, string, error) {
+			resp, err := ec2conn.Snapshots([]string{s.snapshotId}, ec2.NewFilter())
+			if err != nil {
+				return nil, "", err
+			}
+
+			if len(resp.Snapshots) == 0 {
+				return nil, "", errors.New("No snapshots found.")
+			}
+
+			return nil, resp.Snapshots[0].Status, nil
+		},
+	}
+
+	_, err = awscommon.WaitForState(&stateChange)
+	if err != nil {
+		err := fmt.Errorf("Error waiting for snapshot: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	state["snapshot_id"] = s.snapshotId
+	return multistep.ActionContinue
+}
+
+func (s *StepSnapshot) Cleanup(state map[string]interface{}) {
+	if s.snapshotId == "" {
+		return
+	}
+
+	_, cancelled := state[multistep.StateCancelled]
+	_, halted := state[multistep.StateHalted]
+
+	if cancelled || halted {
+		ec2conn := state["ec2"].(*ec2.EC2)
+		ui := state["ui"].(packer.Ui)
+		ui.Say("Removing snapshot since we cancelled or halted...")
+		_, err := ec2conn.DeleteSnapshots([]string{s.snapshotId})
+		if err != nil {
+			ui.Error(fmt.Sprintf("Error: %s", err))
+		}
+	}
+}

builder/amazon/chroot/step_source_ami_info.go

@@ -0,0 +1,52 @@
+package chroot
+
+import (
+	"fmt"
+	"github.com/mitchellh/goamz/ec2"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+)
+
+// StepSourceAMIInfo extracts critical information from the source AMI
+// that is used throughout the AMI creation process.
+//
+// Produces:
+//   source_image *ec2.Image - the source AMI info
+type StepSourceAMIInfo struct{}
+
+func (s *StepSourceAMIInfo) Run(state map[string]interface{}) multistep.StepAction {
+	config := state["config"].(*Config)
+	ec2conn := state["ec2"].(*ec2.EC2)
+	ui := state["ui"].(packer.Ui)
+
+	ui.Say("Inspecting the source AMI...")
+	imageResp, err := ec2conn.Images([]string{config.SourceAmi}, ec2.NewFilter())
+	if err != nil {
+		err := fmt.Errorf("Error querying AMI: %s", err)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	if len(imageResp.Images) == 0 {
+		err := fmt.Errorf("Source AMI '%s' was not found!", config.SourceAmi)
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	image := &imageResp.Images[0]
+
+	// It must be EBS-backed otherwise the build won't work
+	if image.RootDeviceType != "ebs" {
+		err := fmt.Errorf("The root device of the source AMI must be EBS-backed.")
+		state["error"] = err
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	state["source_image"] = image
+	return multistep.ActionContinue
+}
+
+func (s *StepSourceAMIInfo) Cleanup(map[string]interface{}) {}

builder/amazon/common/access_config.go

@@ -1,13 +1,17 @@
 package common
 
 import (
+	"fmt"
 	"github.com/mitchellh/goamz/aws"
+	"strings"
+	"unicode"
 )
 
 // AccessConfig is for common configuration related to AWS access
 type AccessConfig struct {
 	AccessKey string `mapstructure:"access_key"`
 	SecretKey string `mapstructure:"secret_key"`
+	RawRegion string `mapstructure:"region"`
 }
 
 // Auth returns a valid aws.Auth object for access to AWS services, or
@@ -16,6 +20,28 @@ func (c *AccessConfig) Auth() (aws.Auth, error) {
 	return aws.GetAuth(c.AccessKey, c.SecretKey)
 }
 
+// Region returns the aws.Region object for access to AWS services, requesting
+// the region from the instance metadata if possible.
+func (c *AccessConfig) Region() (aws.Region, error) {
+	if c.RawRegion != "" {
+		return aws.Regions[c.RawRegion], nil
+	}
+
+	md, err := aws.GetMetaData("placement/availability-zone")
+	if err != nil {
+		return aws.Region{}, err
+	}
+
+	region := strings.TrimRightFunc(string(md), unicode.IsLetter)
+	return aws.Regions[region], nil
+}
+
 func (c *AccessConfig) Prepare() []error {
+	if c.RawRegion != "" {
+		if _, ok := aws.Regions[c.RawRegion]; !ok {
+			return []error{fmt.Errorf("Unknown region: %s", c.RawRegion)}
+		}
+	}
+
 	return nil
 }

builder/amazon/common/access_config_test.go

@@ -0,0 +1,27 @@
+package common
+
+import (
+	"testing"
+)
+
+func testAccessConfig() *AccessConfig {
+	return &AccessConfig{}
+}
+
+func TestAccessConfigPrepare_Region(t *testing.T) {
+	c := testAccessConfig()
+	c.RawRegion = ""
+	if err := c.Prepare(); err != nil {
+		t.Fatalf("shouldn't have err: %s", err)
+	}
+
+	c.RawRegion = "us-east-12"
+	if err := c.Prepare(); err == nil {
+		t.Fatal("should have error")
+	}
+
+	c.RawRegion = "us-east-1"
+	if err := c.Prepare(); err != nil {
+		t.Fatalf("shouldn't have err: %s", err)
+	}
+}

builder/amazon/common/instance.go

@@ -11,17 +11,38 @@ import (
 
 type StateChangeConf struct {
 	Conn      *ec2.EC2
-	Instance  *ec2.Instance
 	Pending   []string
+	Refresh   func() (interface{}, string, error)
 	StepState map[string]interface{}
 	Target    string
 }
 
-func WaitForState(conf *StateChangeConf) (i *ec2.Instance, err error) {
-	log.Printf("Waiting for instance state to become: %s", conf.Target)
+func InstanceStateRefreshFunc(conn *ec2.EC2, i *ec2.Instance) func() (interface{}, string, error) {
+	return func() (interface{}, string, error) {
+		resp, err := conn.Instances([]string{i.InstanceId}, ec2.NewFilter())
+		if err != nil {
+			return nil, "", err
+		}
+
+		i = &resp.Reservations[0].Instances[0]
+		return i, i.State.Name, nil
+	}
+}
+
+func WaitForState(conf *StateChangeConf) (i interface{}, err error) {
+	log.Printf("Waiting for state to become: %s", conf.Target)
+
+	for {
+		var currentState string
+		i, currentState, err = conf.Refresh()
+		if err != nil {
+			return
+		}
+
+		if currentState == conf.Target {
+			return
+		}
 
-	i = conf.Instance
-	for i.State.Name != conf.Target {
 		if conf.StepState != nil {
 			if _, ok := conf.StepState[multistep.StateCancelled]; ok {
 				return nil, errors.New("interrupted")
@@ -30,24 +51,17 @@ func WaitForState(conf *StateChangeConf) (i *ec2.Instance, err error) {
 
 		found := false
 		for _, allowed := range conf.Pending {
-			if i.State.Name == allowed {
+			if currentState == allowed {
 				found = true
 				break
 			}
 		}
 
 		if !found {
-			fmt.Errorf("unexpected state '%s', wanted target '%s'", i.State.Name, conf.Target)
+			fmt.Errorf("unexpected state '%s', wanted target '%s'", currentState, conf.Target)
 			return
 		}
 
-		var resp *ec2.InstancesResp
-		resp, err = conf.Conn.Instances([]string{i.InstanceId}, ec2.NewFilter())
-		if err != nil {
-			return
-		}
-
-		i = &resp.Reservations[0].Instances[0]
 		time.Sleep(2 * time.Second)
 	}
 

builder/amazon/common/run_config.go

@@ -3,14 +3,12 @@ package common
 import (
 	"errors"
 	"fmt"
-	"github.com/mitchellh/goamz/aws"
 	"time"
 )
 
 // RunConfig contains configuration for running an instance from a source
 // AMI and details on how to access that launched image.
 type RunConfig struct {
-	Region          string
 	SourceAmi       string `mapstructure:"source_ami"`
 	InstanceType    string `mapstructure:"instance_type"`
 	RawSSHTimeout   string `mapstructure:"ssh_timeout"`
@@ -45,12 +43,6 @@ func (c *RunConfig) Prepare() []error {
 		errs = append(errs, errors.New("An instance_type must be specified"))
 	}
 
-	if c.Region == "" {
-		errs = append(errs, errors.New("A region must be specified"))
-	} else if _, ok := aws.Regions[c.Region]; !ok {
-		errs = append(errs, fmt.Errorf("Unknown region: %s", c.Region))
-	}
-
 	if c.SSHUsername == "" {
 		errs = append(errs, errors.New("An ssh_username must be specified"))
 	}

builder/amazon/common/run_config_test.go

@@ -16,7 +16,6 @@ func init() {
 
 func testConfig() *RunConfig {
 	return &RunConfig{
-		Region:       "us-east-1",
 		SourceAmi:    "abcd",
 		InstanceType: "m1.small",
 		SSHUsername:  "root",
@@ -39,24 +38,6 @@ func TestRunConfigPrepare_InstanceType(t *testing.T) {
 	}
 }
 
-func TestRunConfigPrepare_Region(t *testing.T) {
-	c := testConfig()
-	c.Region = ""
-	if err := c.Prepare(); len(err) != 1 {
-		t.Fatalf("err: %s", err)
-	}
-
-	c.Region = "us-east-12"
-	if err := c.Prepare(); len(err) != 1 {
-		t.Fatalf("err: %s", err)
-	}
-
-	c.Region = "us-east-1"
-	if err := c.Prepare(); len(err) != 0 {
-		t.Fatalf("err: %s", err)
-	}
-}
-
 func TestRunConfigPrepare_SourceAmi(t *testing.T) {
 	c := testConfig()
 	c.SourceAmi = ""

builder/amazon/common/step_run_source_instance.go

@@ -62,12 +62,13 @@ func (s *StepRunSourceInstance) Run(state map[string]interface{}) multistep.Step
 	ui.Say(fmt.Sprintf("Waiting for instance (%s) to become ready...", s.instance.InstanceId))
 	stateChange := StateChangeConf{
 		Conn:      ec2conn,
-		Instance:  s.instance,
 		Pending:   []string{"pending"},
 		Target:    "running",
+		Refresh:   InstanceStateRefreshFunc(ec2conn, s.instance),
 		StepState: state,
 	}
-	s.instance, err = WaitForState(&stateChange)
+	latestInstance, err := WaitForState(&stateChange)
+	s.instance = latestInstance.(*ec2.Instance)
 	if err != nil {
 		err := fmt.Errorf("Error waiting for instance (%s) to become ready: %s", s.instance.InstanceId, err)
 		state["error"] = err
@@ -95,10 +96,10 @@ func (s *StepRunSourceInstance) Cleanup(state map[string]interface{}) {
 	}
 
 	stateChange := StateChangeConf{
-		Conn:     ec2conn,
-		Instance: s.instance,
-		Pending:  []string{"pending", "running", "shutting-down", "stopped", "stopping"},
-		Target:   "running",
+		Conn:    ec2conn,
+		Pending: []string{"pending", "running", "shutting-down", "stopped", "stopping"},
+		Refresh: InstanceStateRefreshFunc(ec2conn, s.instance),
+		Target:  "running",
 	}
 
 	WaitForState(&stateChange)

builder/amazon/ebs/builder.go

@@ -8,7 +8,6 @@ package ebs
 import (
 	"errors"
 	"fmt"
-	"github.com/mitchellh/goamz/aws"
 	"github.com/mitchellh/goamz/ec2"
 	"github.com/mitchellh/multistep"
 	awscommon "github.com/mitchellh/packer/builder/amazon/common"
@@ -67,9 +66,9 @@ func (b *Builder) Prepare(raws ...interface{}) error {
 }
 
 func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packer.Artifact, error) {
-	region, ok := aws.Regions[b.config.Region]
-	if !ok {
-		panic("region not found")
+	region, err := b.config.Region()
+	if err != nil {
+		return nil, err
 	}
 
 	auth, err := b.config.AccessConfig.Auth()

builder/amazon/ebs/step_create_ami.go

@@ -52,7 +52,7 @@ func (s *stepCreateAMI) Run(state map[string]interface{}) multistep.StepAction {
 	// Set the AMI ID in the state
 	ui.Say(fmt.Sprintf("AMI: %s", createResp.ImageId))
 	amis := make(map[string]string)
-	amis[config.Region] = createResp.ImageId
+	amis[ec2conn.Region.Name] = createResp.ImageId
 	state["amis"] = amis
 
 	// Wait for the image to become ready

builder/amazon/ebs/step_stop_instance.go

@@ -29,12 +29,13 @@ func (s *stepStopInstance) Run(state map[string]interface{}) multistep.StepActio
 	ui.Say("Waiting for the instance to stop...")
 	stateChange := awscommon.StateChangeConf{
 		Conn:      ec2conn,
-		Instance:  instance,
 		Pending:   []string{"running", "stopping"},
 		Target:    "stopped",
+		Refresh:   awscommon.InstanceStateRefreshFunc(ec2conn, instance),
 		StepState: state,
 	}
-	instance, err = awscommon.WaitForState(&stateChange)
+	instanceRaw, err := awscommon.WaitForState(&stateChange)
+	instance = instanceRaw.(*ec2.Instance)
 	if err != nil {
 		err := fmt.Errorf("Error waiting for instance to stop: %s", err)
 		state["error"] = err

builder/amazon/instance/builder.go

@@ -5,7 +5,6 @@ package instance
 import (
 	"errors"
 	"fmt"
-	"github.com/mitchellh/goamz/aws"
 	"github.com/mitchellh/goamz/ec2"
 	"github.com/mitchellh/multistep"
 	awscommon "github.com/mitchellh/packer/builder/amazon/common"
@@ -134,9 +133,9 @@ func (b *Builder) Prepare(raws ...interface{}) error {
 }
 
 func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packer.Artifact, error) {
-	region, ok := aws.Regions[b.config.Region]
-	if !ok {
-		panic("region not found")
+	region, err := b.config.Region()
+	if err != nil {
+		return nil, err
 	}
 
 	auth, err := b.config.AccessConfig.Auth()

builder/amazon/instance/step_register_ami.go

@@ -50,7 +50,7 @@ func (s *StepRegisterAMI) Run(state map[string]interface{}) multistep.StepAction
 	// Set the AMI ID in the state
 	ui.Say(fmt.Sprintf("AMI: %s", registerResp.ImageId))
 	amis := make(map[string]string)
-	amis[config.Region] = registerResp.ImageId
+	amis[ec2conn.Region.Name] = registerResp.ImageId
 	state["amis"] = amis
 
 	// Wait for the image to become ready

communicator/ssh/communicator.go

@@ -87,6 +87,7 @@ func (c *comm) Start(cmd *packer.RemoteCmd) (err error) {
 			}
 		}
 
+		log.Printf("remote command exited with '%d': %s", exitStatus, cmd.Command)
 		cmd.SetExited(exitStatus)
 	}()
 

config.go

@@ -20,6 +20,7 @@ const defaultConfig = `
 
 	"builders": {
 		"amazon-ebs": "packer-builder-amazon-ebs",
+		"amazon-chroot": "packer-builder-amazon-chroot",
 		"amazon-instance": "packer-builder-amazon-instance",
 		"digitalocean": "packer-builder-digitalocean",
 		"virtualbox": "packer-builder-virtualbox",

plugin/builder-amazon-chroot/main.go

@@ -0,0 +1,10 @@
+package main
+
+import (
+	"github.com/mitchellh/packer/builder/amazon/chroot"
+	"github.com/mitchellh/packer/packer/plugin"
+)
+
+func main() {
+	plugin.ServeBuilder(new(chroot.Builder))
+}

plugin/builder-amazon-chroot/main_test.go

@@ -0,0 +1 @@
+package main

website/source/docs/builders/amazon-chroot.html.markdown

@@ -0,0 +1,177 @@
+---
+layout: "docs"
+page_title: "Amazon AMI Builder (chroot)"
+---
+
+# AMI Builder (chroot)
+
+Type: `amazon-chroot`
+
+The `amazon-chroot` builder is able to create Amazon AMIs backed by
+an EBS volume as the root device. For more information on the difference
+between instance storage and EBS-backed instances, see the
+["storage for the root device" section in the EC2 documentation](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ComponentsAMIs.html#storage-for-the-root-device).
+
+The difference between this builder and the `amazon-ebs` builder is that
+this builder is able to build an EBS-backed AMI without launching a new
+EC2 instance. This can dramatically speed up AMI builds for organizations
+who need the extra fast build.
+
+<div class="alert alert-block alert-warn">
+<p><strong>This is an advanced builder.</strong> If you're just getting
+started with Packer, we recommend starting with the
+<a href="/docs/builders/amazon-ebs.html">amazon-ebs builder</a>, which is
+much easier to use.</p>
+</div>
+
+The builder does _not_ manage AMIs. Once it creates an AMI and stores it
+in your account, it is up to you to use, delete, etc. the AMI.
+
+## How Does it Work?
+
+This builder works by creating a new EBS volume from an existing source AMI
+and attaching it into an already-running EC2 instance. One attached, a
+[chroot](http://en.wikipedia.org/wiki/Chroot) is used to provision the
+system within that volume. After provisioning, the volume is detached,
+snapshotted, and an AMI is made.
+
+Using this process, minutes can be shaved off the AMI creation process
+because a new EC2 instance doesn't need to be launched.
+
+There are some restrictions, however. The host EC2 instance where the
+volume is attached to must be a similar system (generally the same OS
+version, kernel versions, etc.) as the AMI being built. Additionally,
+this process is much more expensive because the EC2 instance must be kept
+running persistently in order to build AMIs, whereas the other AMI builders
+start instances on-demand to build AMIs as needed.
+
+## Configuration Reference
+
+There are many configuration options available for the builder. They are
+segmented below into two categories: required and optional parameters. Within
+each category, the available configuration keys are alphabetized.
+
+Required:
+
+* `access_key` (string) - The access key used to communicate with AWS.
+  If not specified, Packer will attempt to read this from environmental
+  variables `AWS_ACCESS_KEY_ID` or `AWS_ACCESS_KEY` (in that order).
+  If the environmental variables aren't set and Packer is running on
+  an EC2 instance, Packer will check the instance metadata for IAM role
+  keys.
+
+* `ami_name` (string) - The name of the resulting AMI that will appear
+  when managing AMIs in the AWS console or via APIs. This must be unique.
+  To help make this unique, certain template parameters are available for
+  this value, which are documented below.
+
+* `secret_key` (string) - The secret key used to communicate with AWS.
+  If not specified, Packer will attempt to read this from environmental
+  variables `AWS_SECRET_ACCESS_KEY` or `AWS_SECRET_KEY` (in that order).
+  If the environmental variables aren't set and Packer is running on
+  an EC2 instance, Packer will check the instance metadata for IAM role
+  keys.
+
+* `source_ami` (string) - The source AMI whose root volume will be copied
+  and provisioned on the currently running instance. This must be an
+  EBS-backed AMI with a root volume snapshot that you have access to.
+
+Optional:
+
+* `chroot_mounts` (list of list of strings) - This is a list of additional
+  devices to mount into the chroot environment. This configuration parameter
+  requires some additional documentation which is in the "Chroot Mounts" section
+  below. Please read that section for more information on how to use this.
+
+* `copy_files` (list of strings) - Paths to files on the running EC2 instance
+  that will be copied into the chroot environment prior to provisioning.
+  This is useful, for example, to copy `/etc/resolv.conf` so that DNS lookups
+  work.
+
+* `device_path` (string) - The path to the device where the root volume
+  of the source AMI will be attached. This defaults to "" (empty string),
+  which forces Packer to find an open device automatically.
+
+* `mount_command` (string) - The command to use to mount devices. This
+  defaults to "mount". This may be useful to set if you want to set
+  environmental variables or perhaps run it with `sudo` or so on.
+
+* `mount_path` (string) - The path where the volume will be mounted. This is
+  where the chroot environment will be. This defaults to
+  `packer-amazon-chroot-volumes/{{.Device}}`. This is a configuration
+  template where the `.Device` variable is replaced with the name of the
+  device where the volume is attached.
+
+* `unmount_command` (string) - Just like `mount_command`, except this is
+  the command to unmount devices.
+
+## Basic Example
+
+Here is a basic example. It is completely valid except for the access keys:
+
+<pre class="prettyprint">
+{
+  "type": "amazon-chroot",
+  "access_key": "YOUR KEY HERE",
+  "secret_key": "YOUR SECRET KEY HERE",
+  "source_ami": "ami-e81d5881",
+  "ami_name": "packer-amazon-chroot {{.CreateTime}}"
+}
+</pre>
+
+## AMI Name Variables
+
+The AMI name specified by the `ami_name` configuration variable is actually
+treated as a [configuration template](/docs/templates/configuration-templates.html).
+Packer provides a set of variables that it will replace
+within the AMI name. This helps ensure the AMI name is unique, as AWS requires.
+
+The available variables are shown below:
+
+* `CreateTime` - This will be replaced with the Unix timestamp of when
+  the AMI was built.
+
+## Chroot Mounts
+
+The `chroot_mounts` configuration can be used to mount additional devices
+within the chroot. By default, the following additional mounts are added
+into the chroot by Packer:
+
+* `/proc` (proc)
+* `/sys` (sysfs)
+* `/dev` (bind to real `/dev`)
+* `/dev/pts` (devpts)
+* `/proc/sys/fs/binfmt_misc` (binfmt_misc)
+
+These default mounts are usually good enough for anyone and are sane
+defaults. However, if you want to change or add the mount points, you may
+using the `chroot_mounts` configuration. Here is an example configuration:
+
+<pre class="prettyprint">
+{
+  "chroot_mounts": [
+    ["proc", "proc", "/proc"],
+    ["bind", "/dev", "/dev"]
+  ]
+}
+</pre>
+
+`chroot_mounts` is a list of a 3-tuples of strings. The three components
+of the 3-tuple, in order, are:
+
+* The filesystem type. If this is "bind", then Packer will properly bind
+  the filesystem to another mount point.
+
+* The source device.
+
+* The mount directory.
+
+## Parallelism
+
+A quick note on parallelism: it is perfectly safe to run multiple
+_separate_ Packer processes with the `amazon-chroot` builder on the same
+EC2 instance. In fact, this is recommended as a way to push the most performance
+out of your AMI builds.
+
+Packer properly obtains a process lock for the parallelism-sensitive parts
+of its internals such as finding an available device.

website/source/docs/builders/amazon.html.markdown

@@ -18,6 +18,13 @@ AMI. Packer supports the following builders at the moment:
   instance-store AMIs by launching and provisioning a source instance, then
   rebundling it and uploading it to S3.
 
+* [amazon-chroot](/docs/builders/amazon-chroot.html) - Create EBS-backed AMIs
+  from an existing EC2 instance by mounting the root device and using a
+  [Chroot](http://en.wikipedia.org/wiki/Chroot) environment to provision
+  that device. This is an **advanced builder and should not be used by
+  newcomers**. However, it is also the fastest way to build an EBS-backed
+  AMI since no new EC2 instance needs to be launched.
+
 <div class="alert alert-block alert-info">
 <strong>Don't know which builder to use?</strong> If in doubt, use the
 <a href="/docs/builders/amazon-ebs.html">amazon-ebs builder</a>. It is