Valadating early ⏰

builder/amazon/common/run_config.go

@@ -76,11 +76,24 @@ func (c *RunConfig) Prepare(ctx *interpolate.Context) []error {
 		c.RunTags = make(map[string]string)
 	}
 
+	if c.SSHPrivateIp && c.SSHInterface {
+		errs = append(errs, errors.New("ssh_interface and ssh_private_ip should not both be specified"))
+	}
+
 	// Legacy configurable
 	if c.SSHPrivateIp {
 		c.SSHInterface = "private_ip"
 	}
 
+	// Valadating ssh_interface
+	if c.SSHInterface != "public_ip" ||
+		c.SSHInterface != "private_ip" ||
+		c.SSHInterface != "public_dns" ||
+		c.SSHInterface != "private_dns" ||
+		c.SSHInterface != "" {
+		errs = append(errs, errors.New("Unknown interface type: %s", SSHInterface))
+	}
+
 	// Validation
 	errs := c.Comm.Prepare(ctx)
 	if c.SSHKeyPairName != "" {

builder/amazon/common/ssh.go

@@ -51,7 +51,7 @@ func SSHHost(e ec2Describer, sshInterface string) func(multistep.StateBag) (stri
 						host = *i.PrivateDnsName
 					}
 				default:
-					return "", fmt.Errorf("unknown interface type: %s", sshInterface)
+					panic(fmt.Sprintf("Unknown interface type: %s", sshInterface))
 				}
 			} else if i.VpcId != nil && *i.VpcId != "" {
 				if i.PublicIpAddress != nil && *i.PublicIpAddress != "" {