add "command" parameter to docker provisioning

setting a "command" will set the container command, i.e. will override
the default argument executed when the container starts. It supports
template expansion.

cmd/vm_exec.go

@@ -84,7 +84,7 @@ func execDocker(ctx context.Context, v *virter.Virter, s *virter.ProvisionDocker
 		log.Fatal(err)
 	}
 
-	containerCfg := containerapi.NewContainerConfig("virter-"+strings.Join(vmNames, "-"), s.Image, s.Env)
+	containerCfg := containerapi.NewContainerConfig("virter-"+strings.Join(vmNames, "-"), s.Image, s.Env, containerapi.WithCommand(s.Command...))
 
 	return v.VMExecDocker(ctx, containerProvider, vmNames, containerCfg, privateKey, s.Copy)
 }

doc/provisioning.md

@@ -26,6 +26,7 @@ A `docker` provisioning step allows specifying a Docker image to run provisionin
 The Docker provisioning step can be parameterized using the following configuration options:
 * `image` is the Docker image used to provision the VM. It follows the standard Docker format of `<repository>/<image>:<tag>`. This is a Go template.
 * `env` is a map of environment variables to be passed to the Docker container, in `KEY=value` format. The values are Go templates.
+* `command` is a string array and sets the command to execute in the container (basically `<args>...` in `docker run <image> <args>...`). The items are Go templates.
 
   Note that Virter already passes two environment variables by default:
   * `TARGETS` is a comma separated list of all VMs to run the provisioning on.

internal/virter/image.go

@@ -123,7 +123,7 @@ func (v *Virter) imageBuildProvisionCommit(ctx context.Context, tools ImageBuild
 
 	for _, s := range buildConfig.ProvisionConfig.Steps {
 		if s.Docker != nil {
-			containerCfg := containerapi.NewContainerConfig(buildConfig.ContainerName, s.Docker.Image, s.Docker.Env)
+			containerCfg := containerapi.NewContainerConfig(buildConfig.ContainerName, s.Docker.Image, s.Docker.Env, containerapi.WithCommand(s.Docker.Command...))
 			err = v.VMExecDocker(ctx, tools.ContainerProvider, vmNames, containerCfg, sshPrivateKey, nil)
 		} else if s.Shell != nil {
 			err = v.VMExecShell(ctx, vmNames, sshPrivateKey, s.Shell)

internal/virter/provision.go

@@ -14,9 +14,10 @@ import (
 
 // ProvisionDockerStep is a single provisioniong step executed in a docker container
 type ProvisionDockerStep struct {
-	Image string                   `toml:"image"`
-	Env   map[string]string        `toml:"env"`
-	Copy  *ProvisionDockerCopyStep `toml:"copy"`
+	Image   string                   `toml:"image"`
+	Env     map[string]string        `toml:"env"`
+	Command []string                 `toml:"command"`
+	Copy    *ProvisionDockerCopyStep `toml:"copy"`
 }
 
 type ProvisionDockerCopyStep struct {
@@ -134,10 +135,14 @@ func newProvisionConfigReader(provReader io.Reader, provOpt ProvisionOption) (Pr
 				return pc, fmt.Errorf("failed to execute template for docker.image for step %d: %w", i, err)
 			}
 
-			if err := executeTemplates(s.Docker.Env, pc.Values); err != nil {
+			if err := executeTemplateMap(s.Docker.Env, pc.Values); err != nil {
 				return pc, fmt.Errorf("failed to execute template for docker.env for step %d: %w", i, err)
 			}
 
+			if err := executeTemplateArray(s.Docker.Command, pc.Values); err != nil {
+				return pc, fmt.Errorf("failed to execute tempalte for docker.command for step %d: %w", i, err)
+			}
+
 			if copyStep := s.Docker.Copy; copyStep != nil {
 				if copyStep.Dest, err = executeTemplate(copyStep.Dest, pc.Values); err != nil {
 					return pc, fmt.Errorf("failed to execute template for docker.copy.dest for step %d: %w", i, err)
@@ -146,7 +151,7 @@ func newProvisionConfigReader(provReader io.Reader, provOpt ProvisionOption) (Pr
 		} else if s.Shell != nil {
 			s.Shell.Env = mergeEnv(&pc.Env, &s.Shell.Env)
 
-			if err := executeTemplates(s.Shell.Env, pc.Values); err != nil {
+			if err := executeTemplateMap(s.Shell.Env, pc.Values); err != nil {
 				return pc, fmt.Errorf("failed to execute template for shell.env for step %d: %w", i, err)
 			}
 		} else if s.Rsync != nil {
@@ -171,7 +176,7 @@ func genValueMap(provOpt ProvisionOption) (map[string]interface{}, error) {
 	return base, nil
 }
 
-func executeTemplates(templates map[string]string, templateData map[string]string) error {
+func executeTemplateMap(templates map[string]string, templateData map[string]string) error {
 	for k, v := range templates {
 		result, err := executeTemplate(v, templateData)
 		if err != nil {
@@ -182,6 +187,17 @@ func executeTemplates(templates map[string]string, templateData map[string]strin
 	return nil
 }
 
+func executeTemplateArray(templates []string, templateData map[string]string) error {
+	for i, t := range templates {
+		result, err := executeTemplate(t, templateData)
+		if err != nil {
+			return err
+		}
+		templates[i] = result
+	}
+	return nil
+}
+
 func executeTemplate(templateText string, templateData map[string]string) (string, error) {
 	tmpl, err := template.New("").Option("missingkey=error").Parse(templateText)
 	if err != nil {

internal/virter/provision_test.go

@@ -122,6 +122,7 @@ func TestNewProvisionConfigTemplate(t *testing.T) {
 [[steps]]
 [steps.docker]
 image = "some-image"
+command = ["exit", "0"]
 [steps.docker.env]
 foo = "bar"
 
@@ -144,6 +145,7 @@ ShellEnv = "default-value"
 [[steps]]
 [steps.docker]
 image = "{{.DockerImage}}"
+command = ["echo", "{{.DockerCommandArg}}"]
 [steps.docker.env]
 foo = "hello {{.DockerEnv}}"
 
@@ -191,6 +193,7 @@ foo = "{{.ShellEnv"
 				ProvisionStep{
 					Docker: &ProvisionDockerStep{
 						Image: "some-image",
+						Command: []string{"exit", "0"},
 						Env:   map[string]string{"foo": "bar"},
 					},
 				},
@@ -214,13 +217,15 @@ foo = "{{.ShellEnv"
 				Overrides: []string{
 					"values.DockerImage=template-image",
 					"values.DockerEnv=template-value",
+					"values.DockerCommandArg=template-arg",
 					"values.RsyncSource=template-source",
 				},
 			},
 			[]ProvisionStep{
 				ProvisionStep{
 					Docker: &ProvisionDockerStep{
 						Image: "template-image",
+						Command: []string{"echo", "template-arg"},
 						Env:   map[string]string{"foo": "hello template-value"},
 					},
 				},