builder/docker: customize run command [GH-648]

CHANGELOG.md

@@ -45,6 +45,8 @@ IMPROVEMENTS:
   "Packer Builder" so that they are easily recognizable. [GH-642]
 * builder/amazon/all: Copying AMIs to multiple regions now happens
   in parallel. [GH-495]
+* builder/docker: A "run\_command" can be specified, configuring how
+  the container is started. [GH-648]
 * builder/openstack: In debug mode, the generated SSH keypair is saved
   so you can SSH into the machine. [GH-746]
 * builder/qemu: Floppy files are supported. [GH-686]

builder/docker/builder.go

@@ -25,7 +25,7 @@ func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
 }
 
 func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packer.Artifact, error) {
-	driver := &DockerDriver{Ui: ui}
+	driver := &DockerDriver{Tpl: b.config.tpl, Ui: ui}
 	if err := driver.Verify(); err != nil {
 		return nil, err
 	}

builder/docker/config.go

@@ -12,6 +12,7 @@ type Config struct {
 	ExportPath string `mapstructure:"export_path"`
 	Image      string
 	Pull       bool
+	RunCommand []string `mapstructure:"run_command"`
 
 	tpl *packer.ConfigTemplate
 }
@@ -28,6 +29,17 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 		return nil, nil, err
 	}
 
+	// Defaults
+	if len(c.RunCommand) == 0 {
+		c.RunCommand = []string{
+			"run",
+			"-d", "-i", "-t",
+			"-v", "{{.Volumes}}",
+			"{{.Image}}",
+			"/bin/bash",
+		}
+	}
+
 	// Default Pull if it wasn't set
 	hasPull := false
 	for _, k := range md.Keys {

builder/docker/driver.go

@@ -28,5 +28,12 @@ type Driver interface {
 // ContainerConfig is the configuration used to start a container.
 type ContainerConfig struct {
 	Image      string
+	RunCommand []string
 	Volumes    map[string]string
 }
+
+// This is the template that is used for the RunCommand in the ContainerConfig.
+type startContainerTemplate struct {
+	Image   string
+	Volumes string
+}

builder/docker/driver_docker.go

@@ -12,6 +12,7 @@ import (
 
 type DockerDriver struct {
 	Ui  packer.Ui
+	Tpl *packer.ConfigTemplate
 }
 
 func (d *DockerDriver) Export(id string, dst io.Writer) error {
@@ -40,19 +41,29 @@ func (d *DockerDriver) Pull(image string) error {
 }
 
 func (d *DockerDriver) StartContainer(config *ContainerConfig) (string, error) {
-	// Args that we're going to pass to Docker
+	// Build up the template data
-	args := []string{"run", "-d", "-i", "-t"}
+	var tplData startContainerTemplate
-
+	tplData.Image = config.Image
 	if len(config.Volumes) > 0 {
 		volumes := make([]string, 0, len(config.Volumes))
 		for host, guest := range config.Volumes {
 			volumes = append(volumes, fmt.Sprintf("%s:%s", host, guest))
 		}
 
-		args = append(args, "-v", strings.Join(volumes, ","))
+		tplData.Volumes = strings.Join(volumes, ",")
 	}
 
-	args = append(args, config.Image, "/bin/bash")
+	// Args that we're going to pass to Docker
+	args := config.RunCommand
+	for i, v := range args {
+		var err error
+		args[i], err = d.Tpl.Process(v, &tplData)
+		if err != nil {
+			return "", err
+		}
+	}
+	d.Ui.Message(fmt.Sprintf(
+		"Run command: docker %s", strings.Join(args, " ")))
 
 	// Start the container
 	var stdout, stderr bytes.Buffer

builder/docker/step_run.go

@@ -18,12 +18,13 @@ func (s *StepRun) Run(state multistep.StateBag) multistep.StepAction {
 
 	runConfig := ContainerConfig{
 		Image:      config.Image,
+		RunCommand: config.RunCommand,
 		Volumes: map[string]string{
 			tempDir: "/packer-files",
 		},
 	}
 
-	ui.Say("Starting docker container with /bin/bash")
+	ui.Say("Starting docker container...")
 	containerId, err := driver.StartContainer(&runConfig)
 	if err != nil {
 		err := fmt.Errorf("Error running container: %s", err)

website/source/docs/builders/docker.html.markdown

@@ -59,6 +59,11 @@ Optional:
   `docker pull` prior to use. Otherwise, it is assumed the image already
   exists and can be used. This defaults to true if not set.
 
+* `run_command` (array of strings) - An array of arguments to pass to
+  `docker` in order to run the container. By default this is set to
+  `["run", "-d", "-i", "-t", "-v", "{{.Volumes}}", "{{.Image}}", "/bin/bash"]`.
+  As you can see, you have a couple template variables to customize, as well.
+
 ## Using the generated artifact
 
 Once the tar artifact has been generated, you will likely want to import, tag,