Allow EC2 fleet packer instances to run in parallel

Without conflicting over the name of the launch template that they create/delete.

Previously, the launch template name was just hard coded to `packer-fleet-launch-template`, but since AWS enforces unique template names within an account, this caused simultaneously running packer instances to hit template-already-exists errors when creating their templates and race-conditions around deleting the template. Now, the template name is randomly generated on each run, so there should be no conflicts.

builder/amazon/common/step_run_spot_instance.go

@@ -14,6 +14,7 @@ import (
 	"github.com/aws/aws-sdk-go/service/ec2"
 
 	"github.com/aws/aws-sdk-go/service/ec2/ec2iface"
+	"github.com/hashicorp/packer/common/random"
 	"github.com/hashicorp/packer/common/retry"
 	"github.com/hashicorp/packer/helper/communicator"
 	"github.com/hashicorp/packer/helper/multistep"
@@ -259,6 +260,14 @@ func (s *StepRunSpotInstance) Run(ctx context.Context, state multistep.StateBag)
 
 	// Create a launch template for the instance
 	ui.Message("Loading User Data File...")
+
+	// Generate a random name to avoid conflicting with other
+	// instances of packer running in this AWS account
+	launchTemplateName := fmt.Sprintf(
+		"packer-fleet-launch-template-%s",
+		random.AlphaNum(7))
+	state.Put("launchTemplateName", launchTemplateName) // For the cleanup step
+
 	userData, err := s.LoadUserData()
 	if err != nil {
 		state.Put("error", err)
@@ -268,7 +277,7 @@ func (s *StepRunSpotInstance) Run(ctx context.Context, state multistep.StateBag)
 	templateData := s.CreateTemplateData(&userData, az, state, marketOptions)
 	launchTemplate := &ec2.CreateLaunchTemplateInput{
 		LaunchTemplateData: templateData,
-		LaunchTemplateName: aws.String("packer-fleet-launch-template"),
+		LaunchTemplateName: aws.String(launchTemplateName),
 		VersionDescription: aws.String("template generated by packer for launching spot instances"),
 	}
 
@@ -294,7 +303,7 @@ func (s *StepRunSpotInstance) Run(ctx context.Context, state multistep.StateBag)
 		LaunchTemplateConfigs: []*ec2.FleetLaunchTemplateConfigRequest{
 			{
 				LaunchTemplateSpecification: &ec2.FleetLaunchTemplateSpecificationRequest{
-					LaunchTemplateName: aws.String("packer-fleet-launch-template"),
+					LaunchTemplateName: aws.String(launchTemplateName),
 					Version:            aws.String("1"),
 				},
 				Overrides: overrides,
@@ -460,6 +469,7 @@ func (s *StepRunSpotInstance) Cleanup(state multistep.StateBag) {
 
 	ec2conn := state.Get("ec2").(*ec2.EC2)
 	ui := state.Get("ui").(packer.Ui)
+	launchTemplateName := state.Get("launchTemplateName").(string)
 
 	// Cancel the spot request if it exists
 	if s.spotRequest != nil {
@@ -494,7 +504,7 @@ func (s *StepRunSpotInstance) Cleanup(state multistep.StateBag) {
 
 	// Delete the launch template used to create the spot fleet
 	deleteInput := &ec2.DeleteLaunchTemplateInput{
-		LaunchTemplateName: aws.String("packer-fleet-launch-template"),
+		LaunchTemplateName: aws.String(launchTemplateName),
 	}
 	if _, err := ec2conn.DeleteLaunchTemplate(deleteInput); err != nil {
 		ui.Error(err.Error())