Add Script Support to Sidecars

docs/tasks.md

@@ -496,6 +496,16 @@ volumes:
     emptyDir: {}
 ```
 
+Sidecars can also run a script, like a Step:
+
+```yaml
+sidecars:
+  image: busybox
+  name: hello-sidecar
+  script: |
+    echo 'Hello from sidecar!'
+```
+
 Note: There is a known bug with Tekton's existing sidecar implementation.
 Tekton uses a specific image, called "nop", to stop sidecars. The "nop" image
 is configurable using a flag of the Tekton controller. If the configured "nop"

examples/taskruns/sidecar-ready-script.yaml

@@ -0,0 +1,30 @@
+apiVersion: tekton.dev/v1alpha1
+kind: TaskRun
+metadata:
+  generateName: sidecar-ready-
+spec:
+  taskSpec:
+    sidecars:
+    - name: slow-sidecar
+      image: ubuntu
+      script: |
+        echo "hello from sidecar" > /shared/message
+      volumeMounts:
+      - name: shared
+        mountPath: /shared
+
+    steps:
+    - name: check-ready
+      image: ubuntu
+      # The step will only succeed if the sidecar has written this file, which
+      # it does 5s after it starts, before it reports Ready.
+      script: cat /shared/message
+      volumeMounts:
+      - name: shared
+        mountPath: /shared
+
+    # Sidecars don't have /workspace mounted by default, so we have to define
+    # our own shared volume.
+    volumes:
+    - name: shared
+      emptyDir: {}

pkg/apis/pipeline/v1alpha1/task_types.go

@@ -60,7 +60,7 @@ type TaskSpec struct {
 
 	// Sidecars are run alongside the Task's step containers. They begin before
 	// the steps start and end after the steps complete.
-	Sidecars []corev1.Container `json:"sidecars,omitempty"`
+	Sidecars []Sidecar `json:"sidecars,omitempty"`
 
 	// Workspaces are the volumes that this Task requires.
 	Workspaces []WorkspaceDeclaration `json:"workspaces,omitempty"`
@@ -70,6 +70,8 @@ type TaskSpec struct {
 // provided by Container.
 type Step = v1alpha2.Step
 
+type Sidecar = v1alpha2.Sidecar
+
 // +genclient
 // +genclient:noStatus
 // +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object

pkg/apis/pipeline/v1alpha2/task_types.go

@@ -81,7 +81,7 @@ type TaskSpec struct {
 
 	// Sidecars are run alongside the Task's step containers. They begin before
 	// the steps start and end after the steps complete.
-	Sidecars []corev1.Container `json:"sidecars,omitempty"`
+	Sidecars []Sidecar `json:"sidecars,omitempty"`
 
 	// Workspaces are the volumes that this Task requires.
 	Workspaces []WorkspaceDeclaration
@@ -98,6 +98,9 @@ type Step struct {
 	Script string `json:"script,omitempty"`
 }
 
+// A sidecar has the same data structure as a Step, consisting of a Container, and optional Script.
+type Sidecar = Step
+
 // +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object
 // TaskList contains a list of Task
 type TaskList struct {

pkg/pod/pod.go

@@ -93,7 +93,7 @@ func MakePod(images pipeline.Images, taskRun *v1alpha1.TaskRun, taskSpec v1alpha
 
 	// Convert any steps with Script to command+args.
 	// If any are found, append an init container to initialize scripts.
-	scriptsInit, stepContainers := convertScripts(images.ShellImage, steps)
+	scriptsInit, stepContainers, sidecarContainers := convertScripts(images.ShellImage, steps, taskSpec.Sidecars)
 	if scriptsInit != nil {
 		initContainers = append(initContainers, *scriptsInit)
 		volumes = append(volumes, scriptsVolume)
@@ -171,9 +171,10 @@ func MakePod(images pipeline.Images, taskRun *v1alpha1.TaskRun, taskSpec v1alpha
 		return nil, err
 	}
 
-	// Merge sidecar containers with step containers.
 	mergedPodContainers := stepContainers
-	for _, sc := range taskSpec.Sidecars {
+
+	// Merge sidecar containers with step containers.
+	for _, sc := range sidecarContainers {
 		sc.Name = names.SimpleNameGenerator.RestrictLength(fmt.Sprintf("%v%v", sidecarPrefix, sc.Name))
 		mergedPodContainers = append(mergedPodContainers, sc)
 	}

pkg/pod/pod_test.go

@@ -355,10 +355,14 @@ func TestMakePod(t *testing.T) {
 				Image:   "primary-image",
 				Command: []string{"cmd"}, // avoid entrypoint lookup.
 			}}},
-			Sidecars: []corev1.Container{{
-				Name:  "sc-name",
-				Image: "sidecar-image",
-			}},
+			Sidecars: []v1alpha1.Sidecar{
+				{
+					Container: corev1.Container{
+						Name:  "sc-name",
+						Image: "sidecar-image",
+					},
+				},
+			},
 		},
 		wantAnnotations: map[string]string{},
 		want: &corev1.PodSpec{
@@ -394,6 +398,76 @@ func TestMakePod(t *testing.T) {
 			}},
 			Volumes: append(implicitVolumes, toolsVolume, downwardVolume),
 		},
+	}, {
+		desc: "sidecar container with script",
+		ts: v1alpha1.TaskSpec{
+			Steps: []v1alpha1.Step{{Container: corev1.Container{
+				Name:    "primary-name",
+				Image:   "primary-image",
+				Command: []string{"cmd"}, // avoid entrypoint lookup.
+			}}},
+			Sidecars: []v1alpha1.Sidecar{
+				{
+					Container: corev1.Container{
+						Name:  "sc-name",
+						Image: "sidecar-image",
+					},
+					Script: "#!/bin/sh\necho hello from sidecar",
+				},
+			},
+		},
+		wantAnnotations: map[string]string{},
+		want: &corev1.PodSpec{
+			RestartPolicy: corev1.RestartPolicyNever,
+			InitContainers: []corev1.Container{
+				{
+					Name:         "place-scripts",
+					Image:        "busybox",
+					Command:      []string{"sh"},
+					TTY:          true,
+					VolumeMounts: []corev1.VolumeMount{scriptsVolumeMount},
+					Args: []string{"-c", `tmpfile="/tekton/scripts/sidecar-script-0-9l9zj"
+touch ${tmpfile} && chmod +x ${tmpfile}
+cat > ${tmpfile} << 'sidecar-script-heredoc-randomly-generated-mz4c7'
+#!/bin/sh
+echo hello from sidecar
+sidecar-script-heredoc-randomly-generated-mz4c7
+`},
+				},
+				placeToolsInit,
+			},
+			Containers: []corev1.Container{{
+				Name:    "step-primary-name",
+				Image:   "primary-image",
+				Command: []string{"/tekton/tools/entrypoint"},
+				Args: []string{
+					"-wait_file",
+					"/tekton/downward/ready",
+					"-wait_file_content",
+					"-post_file",
+					"/tekton/tools/0",
+					"-termination_path",
+					"/tekton/termination",
+					"-entrypoint",
+					"cmd",
+					"--",
+				},
+				Env:                    implicitEnvVars,
+				VolumeMounts:           append([]corev1.VolumeMount{toolsMount, downwardMount}, implicitVolumeMounts...),
+				WorkingDir:             pipeline.WorkspaceDir,
+				Resources:              corev1.ResourceRequirements{Requests: allZeroQty()},
+				TerminationMessagePath: "/tekton/termination",
+			}, {
+				Name:  "sidecar-sc-name",
+				Image: "sidecar-image",
+				Resources: corev1.ResourceRequirements{
+					Requests: nil,
+				},
+				Command:      []string{"/tekton/scripts/sidecar-script-0-9l9zj"},
+				VolumeMounts: []corev1.VolumeMount{scriptsVolumeMount},
+			}},
+			Volumes: append(implicitVolumes, scriptsVolume, toolsVolume, downwardVolume),
+		},
 	}, {
 		desc: "resource request",
 		ts: v1alpha1.TaskSpec{

pkg/pod/script.go

@@ -45,12 +45,12 @@ var (
 	}
 )
 
-// convertScripts converts any steps that specify a Script field into a normal Container.
+// convertScripts converts any steps and sidecars that specify a Script field into a normal Container.
 //
 // It does this by prepending a container that writes specified Script bodies
 // to executable files in a shared volumeMount, then produces Containers that
 // simply run those executable files.
-func convertScripts(shellImage string, steps []v1alpha1.Step) (*corev1.Container, []corev1.Container) {
+func convertScripts(shellImage string, steps []v1alpha1.Step, sidecars []v1alpha1.Sidecar) (*corev1.Container, []corev1.Container, []corev1.Container) {
 	placeScripts := false
 	placeScriptsInit := corev1.Container{
 		Name:         "place-scripts",
@@ -61,7 +61,21 @@ func convertScripts(shellImage string, steps []v1alpha1.Step) (*corev1.Container
 		VolumeMounts: []corev1.VolumeMount{scriptsVolumeMount},
 	}
 
-	var containers []corev1.Container
+	convertedStepContainers := convertListOfSteps(steps, &placeScriptsInit, &placeScripts, "script")
+	sidecarContainers := convertListOfSteps(sidecars, &placeScriptsInit, &placeScripts, "sidecar-script")
+
+	if placeScripts {
+		return &placeScriptsInit, convertedStepContainers, sidecarContainers
+	}
+	return nil, convertedStepContainers, sidecarContainers
+}
+
+// convertListOfSteps does the heavy lifting for convertScripts.
+//
+// It iterates through the list of steps (or sidecars), generates the script file name and heredoc termination string,
+// adds an entry to the init container args, sets up the step container to run the script, and sets the volume mounts.
+func convertListOfSteps(steps []v1alpha1.Step, initContainer *corev1.Container, placeScripts *bool, format string) []corev1.Container {
+	containers := []corev1.Container{}
 	for i, s := range steps {
 		if s.Script == "" {
 			// Nothing to convert.
@@ -81,20 +95,20 @@ func convertScripts(shellImage string, steps []v1alpha1.Step) (*corev1.Container
 
 		// At least one step uses a script, so we should return a
 		// non-nil init container.
-		placeScripts = true
+		*placeScripts = true
 
 		// Append to the place-scripts script to place the
 		// script file in a known location in the scripts volume.
-		tmpFile := filepath.Join(scriptsDir, names.SimpleNameGenerator.RestrictLengthWithRandomSuffix(fmt.Sprintf("script-%d", i)))
+		tmpFile := filepath.Join(scriptsDir, names.SimpleNameGenerator.RestrictLengthWithRandomSuffix(fmt.Sprintf("%s-%d", format, i)))
 		// heredoc is the "here document" placeholder string
 		// used to cat script contents into the file. Typically
 		// this is the string "EOF" but if this value were
 		// "EOF" it would prevent users from including the
 		// string "EOF" in their own scripts. Instead we
 		// randomly generate a string to (hopefully) prevent
 		// collisions.
-		heredoc := names.SimpleNameGenerator.RestrictLengthWithRandomSuffix("script-heredoc-randomly-generated")
-		placeScriptsInit.Args[1] += fmt.Sprintf(`tmpfile="%s"
+		heredoc := names.SimpleNameGenerator.RestrictLengthWithRandomSuffix(fmt.Sprintf("%s-heredoc-randomly-generated", format))
+		initContainer.Args[1] += fmt.Sprintf(`tmpfile="%s"
 touch ${tmpfile} && chmod +x ${tmpfile}
 cat > ${tmpfile} << '%s'
 %s
@@ -110,9 +124,5 @@ cat > ${tmpfile} << '%s'
 		steps[i].VolumeMounts = append(steps[i].VolumeMounts, scriptsVolumeMount)
 		containers = append(containers, steps[i].Container)
 	}
-
-	if placeScripts {
-		return &placeScriptsInit, containers
-	}
-	return nil, containers
+	return containers
 }