simplify things a bit more

builder/amazon/common/ssm/driver.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log"
 	"os/exec"
+	"strconv"
 	"time"
 
 	"github.com/aws/aws-sdk-go/aws"
@@ -20,17 +21,34 @@ import (
 type Session struct {
 	SvcClient             ssmiface.SSMAPI
 	Region                string
-	Input     ssm.StartSessionInput
+	InstanceID            string
+	LocalPort, RemotePort int
+}
+
+func (s Session) buildTunnelInput() *ssm.StartSessionInput {
+	portNumber, localPortNumber := strconv.Itoa(s.RemotePort), strconv.Itoa(s.LocalPort)
+	params := map[string][]*string{
+		"portNumber":      []*string{aws.String(portNumber)},
+		"localPortNumber": []*string{aws.String(localPortNumber)},
+	}
+
+	return &ssm.StartSessionInput{
+		DocumentName: aws.String("AWS-StartPortForwardingSession"),
+		Parameters:   params,
+		Target:       aws.String(s.InstanceID),
+	}
 }
 
 // getCommand return a valid ordered set of arguments to pass to the driver command.
 func (s Session) getCommand(ctx context.Context) ([]string, string, error) {
+	input := s.buildTunnelInput()
+
 	var session *ssm.StartSessionOutput
 	err := retry.Config{
 		ShouldRetry: func(err error) bool { return awserrors.Matches(err, "TargetNotConnected", "") },
 		RetryDelay:  (&retry.Backoff{InitialBackoff: 200 * time.Millisecond, MaxBackoff: 60 * time.Second, Multiplier: 2}).Linear,
 	}.Run(ctx, func(ctx context.Context) (err error) {
-		session, err = s.SvcClient.StartSessionWithContext(ctx, &s.Input)
+		session, err = s.SvcClient.StartSessionWithContext(ctx, input)
 		return err
 	})
 
@@ -49,7 +67,7 @@ func (s Session) getCommand(ctx context.Context) ([]string, string, error) {
 	}
 
 	// AWS session-manager-plugin requires the parameters used in the session to be passed in JSON as well.
-	sessionParameters, err := json.Marshal(s.Input)
+	sessionParameters, err := json.Marshal(input)
 	if err != nil {
 		return nil, "", fmt.Errorf("error encountered in reading session parameter details %s", err)
 	}
@@ -73,7 +91,7 @@ func (s Session) getCommand(ctx context.Context) ([]string, string, error) {
 // created from calling StartSession.
 func (s Session) Start(ctx context.Context, ui packer.Ui) error {
 	for ctx.Err() == nil {
-		log.Printf("ssm: Starting PortForwarding session to instance %q", *s.Input.Target)
+		log.Printf("ssm: Starting PortForwarding session to instance %s", s.InstanceID)
 		args, sessionID, err := s.getCommand(ctx)
 		if sessionID != "" {
 			defer func() {

builder/amazon/common/step_create_ssm_tunnel.go

@@ -3,7 +3,6 @@ package common
 import (
 	"context"
 	"fmt"
-	"strconv"
 	"time"
 
 	"github.com/aws/aws-sdk-go/aws"
@@ -22,7 +21,6 @@ type StepCreateSSMTunnel struct {
 	LocalPortNumber  int
 	RemotePortNumber int
 	SSMAgentEnabled  bool
-	instanceId       string
 	PauseBeforeSSM   time.Duration
 	stopSSMCommand   func()
 }
@@ -62,12 +60,9 @@ func (s *StepCreateSSMTunnel) Run(ctx context.Context, state multistep.StateBag)
 		state.Put("error", err)
 		return multistep.ActionHalt
 	}
-	s.instanceId = aws.StringValue(instance.InstanceId)
 
 	state.Put("sessionPort", s.LocalPortNumber)
 
-	input := s.BuildTunnelInputForInstance(s.instanceId)
-
 	ssmCtx, ssmCancel := context.WithCancel(ctx)
 	s.stopSSMCommand = ssmCancel
 
@@ -75,7 +70,9 @@ func (s *StepCreateSSMTunnel) Run(ctx context.Context, state multistep.StateBag)
 		ssmconn := ssm.New(s.AWSSession)
 		err := pssm.Session{
 			SvcClient:  ssmconn,
-			Input:     input,
+			InstanceID: aws.StringValue(instance.InstanceId),
+			RemotePort: s.RemotePortNumber,
+			LocalPort:  s.LocalPortNumber,
 			Region:     s.Region,
 		}.Start(ssmCtx, ui)
 
@@ -127,19 +124,3 @@ func (s *StepCreateSSMTunnel) ConfigureLocalHostPort(ctx context.Context) error
 	return nil
 
 }
-
-func (s *StepCreateSSMTunnel) BuildTunnelInputForInstance(instance string) ssm.StartSessionInput {
-	dst, src := strconv.Itoa(s.RemotePortNumber), strconv.Itoa(s.LocalPortNumber)
-	params := map[string][]*string{
-		"portNumber":      []*string{aws.String(dst)},
-		"localPortNumber": []*string{aws.String(src)},
-	}
-
-	input := ssm.StartSessionInput{
-		DocumentName: aws.String("AWS-StartPortForwardingSession"),
-		Parameters:   params,
-		Target:       aws.String(instance),
-	}
-
-	return input
-}