add force_pull to docker driver

client/driver/docker.go

@@ -136,6 +136,7 @@ type DockerDriverConfig struct {
 	WorkDir          string              `mapstructure:"work_dir"`           // Working directory inside the container
 	Logging          []DockerLoggingOpts `mapstructure:"logging"`            // Logging options for syslog server
 	Volumes          []string            `mapstructure:"volumes"`            // Host-Volumes to mount in, syntax: /path/to/host/directory:/destination/path/in/container
+	ForcePull        bool                `mapstructure:"force_pull"`         // Always force pull before running image, useful if your tags are mutable
 }
 
 // Validate validates a docker driver config
@@ -331,6 +332,9 @@ func (d *DockerDriver) Validate(config map[string]interface{}) error {
 			"volumes": &fields.FieldSchema{
 				Type: fields.TypeArray,
 			},
+			"force_pull": &fields.FieldSchema{
+				Type: fields.TypeBool,
+			},
 		},
 	}
 
@@ -890,9 +894,11 @@ func (d *DockerDriver) createImage(driverConfig *DockerDriverConfig, client *doc
 	var dockerImage *docker.Image
 	var err error
 	// We're going to check whether the image is already downloaded. If the tag
-	// is "latest" we have to check for a new version every time so we don't
+	// is "latest", or ForcePull is set, we have to check for a new version every time so we don't
 	// bother to check and cache the id here. We'll download first, then cache.
-	if tag != "latest" {
+	if driverConfig.ForcePull {
+		d.logger.Printf("[DEBUG] driver.docker: force pull image '%s:%s' instead of inspecting local", repo, tag)
+	} else if tag != "latest" {
 		dockerImage, err = client.InspectImage(image)
 	}
 

client/driver/docker_test.go

@@ -699,6 +699,35 @@ func TestDockerDriver_Labels(t *testing.T) {
 	}
 }
 
+func TestDockerDriver_ForcePull_IsInvalidConfig(t *testing.T) {
+	task, _, _ := dockerTask()
+	task.Config["force_pull"] = "nothing"
+
+	ctx := testDriverContexts(t, task)
+	defer ctx.AllocDir.Destroy()
+	ctx.DriverCtx.config.Options = map[string]string{"docker.cleanup.image": "false"}
+	driver := NewDockerDriver(ctx.DriverCtx)
+
+	if err := driver.Prestart(ctx.ExecCtx, task); err == nil {
+		t.Fatalf("error expected in prestart")
+	}
+}
+
+func TestDockerDriver_ForcePull(t *testing.T) {
+	task, _, _ := dockerTask()
+	task.Config["force_pull"] = "true"
+
+	client, handle, cleanup := dockerSetup(t, task)
+	defer cleanup()
+
+	waitForExist(t, client, handle.(*DockerHandle))
+
+	_, err := client.InspectContainer(handle.(*DockerHandle).ContainerID())
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+}
+
 func TestDockerDriver_DNS(t *testing.T) {
 	task, _, _ := dockerTask()
 	task.Config["dns_servers"] = []string{"8.8.8.8", "8.8.4.4"}

website/source/docs/drivers/docker.html.md

@@ -164,6 +164,10 @@ The `docker` driver supports the following configuration in the job spec:
 * `interactive` - (Optional) `true` or `false` (default). Keep STDIN open on
   the container.
 
+* `force_pull` - (Optional) `true` or `false` (default). Always pull latest image
+  instead of using existing local image. Should be set to `true` if repository tags
+  are mutable.
+
 * `shm_size` - (Optional) The size (bytes) of /dev/shm for the container.
 
 * `logging` - (Optional) A key-value map of Docker logging options. The default