diff --git a/builder/docker/builder.go b/builder/docker/builder.go
index 89880aacc..702d530ce 100644
--- a/builder/docker/builder.go
+++ b/builder/docker/builder.go
@@ -9,8 +9,10 @@ import (
 	"github.com/mitchellh/packer/packer"
 )
 
-const BuilderId = "packer.docker"
-const BuilderIdImport = "packer.post-processor.docker-import"
+const (
+	BuilderId       = "packer.docker"
+	BuilderIdImport = "packer.post-processor.docker-import"
+)
 
 type Builder struct {
 	config *Config
@@ -54,10 +56,16 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 		&common.StepProvision{},
 	}
 
-	if b.config.Commit {
+	if b.config.Discard {
+		log.Print("[DEBUG] Container will be discarded")
+	} else if b.config.Commit {
+		log.Print("[DEBUG] Container will be committed")
 		steps = append(steps, new(StepCommit))
-	} else {
+	} else if b.config.ExportPath != "" {
+		log.Printf("[DEBUG] Container will be exported to %s", b.config.ExportPath)
 		steps = append(steps, new(StepExport))
+	} else {
+		return nil, ErrArtifactNotUsed
 	}
 
 	// Setup the state bag and initial state for the steps
diff --git a/builder/docker/config.go b/builder/docker/config.go
index 36322080c..dc205eaf0 100644
--- a/builder/docker/config.go
+++ b/builder/docker/config.go
@@ -12,23 +12,33 @@ import (
 	"github.com/mitchellh/packer/template/interpolate"
 )
 
+var (
+	ErrArtifactNotUsed     = fmt.Errorf("No instructions given for handling the artifact; expected commit, discard, or export_path")
+	ErrArtifactUseConflict = fmt.Errorf("Cannot specify more than one of commit, discard, and export_path")
+	ErrExportPathNotFile   = fmt.Errorf("export_path must be a file, not a directory")
+	ErrImageNotSpecified   = fmt.Errorf("Image must be specified")
+)
+
 type Config struct {
 	common.PackerConfig `mapstructure:",squash"`
 	Comm                communicator.Config `mapstructure:",squash"`
 
 	Commit     bool
+	Discard    bool
 	ExportPath string `mapstructure:"export_path"`
 	Image      string
+	Pty        bool
 	Pull       bool
 	RunCommand []string `mapstructure:"run_command"`
 	Volumes    map[string]string
 
+	// This is used to login to dockerhub to pull a private base container
+	// For pushing to dockerhub, see the docker post-processors
 	Login         bool
 	LoginEmail    string `mapstructure:"login_email"`
-	LoginUsername string `mapstructure:"login_username"`
 	LoginPassword string `mapstructure:"login_password"`
 	LoginServer   string `mapstructure:"login_server"`
-	Pty           bool
+	LoginUsername string `mapstructure:"login_username"`
 
 	ctx interpolate.Context
 }
@@ -84,18 +94,20 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 	}
 	if c.Image == "" {
 		errs = packer.MultiErrorAppend(errs,
-			fmt.Errorf("image must be specified"))
+			ErrImageNotSpecified)
 	}
 
-	if c.ExportPath != "" && c.Commit {
-		errs = packer.MultiErrorAppend(errs,
-			fmt.Errorf("both commit and export_path cannot be set"))
+	if (c.ExportPath != "" && c.Commit) || (c.ExportPath != "" && c.Discard) || (c.Commit && c.Discard) {
+		errs = packer.MultiErrorAppend(errs, ErrArtifactUseConflict)
+	}
+
+	if c.ExportPath == "" && !c.Commit && !c.Discard {
+		errs = packer.MultiErrorAppend(errs, ErrArtifactNotUsed)
 	}
 
 	if c.ExportPath != "" {
 		if fi, err := os.Stat(c.ExportPath); err == nil && fi.IsDir() {
-			errs = packer.MultiErrorAppend(errs, fmt.Errorf(
-				"export_path must be a file, not a directory"))
+			errs = packer.MultiErrorAppend(errs, ErrExportPathNotFile)
 		}
 	}