builder/amazon: drop private key if debug mode [GH-373]

CHANGELOG.md

 ## 0.3.6 (unreleased)
 
+IMPROVEMENTS:
+
+* builder/amazon: In `-debug` mode, the keypair used will be saved to
+  the current directory so you can access the machine. [GH-373]
+
 BUG FIXES:
 
 * core: Fix possible panic when ctrl-C during provisioner run.

builder/amazon/common/step_key_pair.go

@@ -8,9 +8,13 @@ import (
 	"github.com/mitchellh/multistep"
 	"github.com/mitchellh/packer/packer"
 	"log"
+	"os"
 )
 
 type StepKeyPair struct {
+	Debug        bool
+	DebugKeyPath string
+
 	keyName string
 }
 
@@ -34,6 +38,23 @@ func (s *StepKeyPair) Run(state map[string]interface{}) multistep.StepAction {
 	state["keyPair"] = keyName
 	state["privateKey"] = keyResp.KeyMaterial
 
+	// If we're in debug mode, output the private key to the working
+	// directory.
+	if s.Debug {
+		ui.Message(fmt.Sprintf("Saving key for debug purposes: %s", s.DebugKeyPath))
+		f, err := os.Create(s.DebugKeyPath)
+		if err != nil {
+			state["error"] = fmt.Errorf("Error saving debug key: %s", err)
+			return multistep.ActionHalt
+		}
+		defer f.Close()
+
+		if _, err := f.Write([]byte(keyResp.KeyMaterial)); err != nil {
+			state["error"] = fmt.Errorf("Error saving debug key: %s", err)
+			return multistep.ActionHalt
+		}
+	}
+
 	return multistep.ActionContinue
 }
 

builder/amazon/ebs/builder.go

@@ -6,6 +6,7 @@
 package ebs
 
 import (
+	"fmt"
 	"github.com/mitchellh/goamz/ec2"
 	"github.com/mitchellh/multistep"
 	awscommon "github.com/mitchellh/packer/builder/amazon/common"
@@ -80,7 +81,10 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 
 	// Build the steps
 	steps := []multistep.Step{
-		&awscommon.StepKeyPair{},
+		&awscommon.StepKeyPair{
+			Debug:        b.config.PackerDebug,
+			DebugKeyPath: fmt.Sprintf("ec2_%s.pem", b.config.PackerBuildName),
+		},
 		&awscommon.StepSecurityGroup{
 			SecurityGroupId: b.config.SecurityGroupId,
 			SSHPort:         b.config.SSHPort,

builder/amazon/instance/builder.go

@@ -184,7 +184,10 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 
 	// Build the steps
 	steps := []multistep.Step{
-		&awscommon.StepKeyPair{},
+		&awscommon.StepKeyPair{
+			Debug:        b.config.PackerDebug,
+			DebugKeyPath: fmt.Sprintf("ec2_%s.pem", b.config.PackerBuildName),
+		},
 		&awscommon.StepSecurityGroup{
 			SecurityGroupId: b.config.SecurityGroupId,
 			SSHPort:         b.config.SSHPort,