add featuregate for k8s 1.28 native sidecar container

Signed-off-by: Benedikt Bongartz <bongartz@klimlive.de>

.chloggen/native_sidecar.yaml

@@ -0,0 +1,16 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. collector, target allocator, auto-instrumentation, opamp, github action)
+component: pkg/sidecar
+
+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add native sidecar injection behind a feature gate which is disabled by default.
+
+# One or more tracking issues related to the change
+issues: [2376]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

pkg/featuregate/featuregate.go

@@ -25,6 +25,19 @@ const (
 )
 
 var (
+	// EnableNativeSidecarContainers is the feature gate that controls whether a
+	// sidecar should be injected as a native sidecar or the classic way.
+	// Native sidecar containers have been available since kubernetes v1.28 in
+	// alpha and v1.29 in beta.
+	// It needs to be enabled with +featureGate=SidecarContainers.
+	// See:
+	// https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/#feature-gates-for-alpha-or-beta-features
+	EnableNativeSidecarContainers = featuregate.GlobalRegistry().MustRegister(
+		"operator.sidecarcontainers.native",
+		featuregate.StageAlpha,
+		featuregate.WithRegisterDescription("controls whether the operator supports sidecar containers as init containers"),
+		featuregate.WithRegisterFromVersion("v0.98.0"),
+	)
 	EnableJavaAutoInstrumentationSupport = featuregate.GlobalRegistry().MustRegister(
 		"operator.autoinstrumentation.java",
 		featuregate.StageBeta,

pkg/sidecar/pod.go

@@ -25,6 +25,7 @@ import (
 	"github.com/open-telemetry/opentelemetry-operator/internal/config"
 	"github.com/open-telemetry/opentelemetry-operator/internal/manifests/collector"
 	"github.com/open-telemetry/opentelemetry-operator/internal/naming"
+	"github.com/open-telemetry/opentelemetry-operator/pkg/featuregate"
 )
 
 const (
@@ -47,7 +48,15 @@ func add(cfg config.Config, logger logr.Logger, otelcol v1beta1.OpenTelemetryCol
 		container.Env = append(container.Env, attributes...)
 	}
 	pod.Spec.InitContainers = append(pod.Spec.InitContainers, otelcol.Spec.InitContainers...)
-	pod.Spec.Containers = append(pod.Spec.Containers, container)
+
+	if featuregate.EnableNativeSidecarContainers.IsEnabled() {
+		policy := corev1.ContainerRestartPolicyAlways
+		container.RestartPolicy = &policy
+		// TODO(frzifus): Add StartupProbe
+		pod.Spec.InitContainers = append(pod.Spec.InitContainers, container)
+	} else {
+		pod.Spec.Containers = append(pod.Spec.Containers, container)
+	}
 	pod.Spec.Volumes = append(pod.Spec.Volumes, otelcol.Spec.Volumes...)
 
 	if pod.Labels == nil {
@@ -71,6 +80,17 @@ func remove(pod corev1.Pod) (corev1.Pod, error) {
 		}
 	}
 	pod.Spec.Containers = containers
+
+	// NOTE: we also remove init containers (native sidecars) since k8s 1.28.
+	// This should have no side effects.
+	var initContainers []corev1.Container
+	for _, initContainer := range pod.Spec.InitContainers {
+		if initContainer.Name != naming.Container() {
+			initContainers = append(initContainers, initContainer)
+		}
+	}
+	pod.Spec.InitContainers = initContainers
+
 	return pod, nil
 }
 
@@ -81,5 +101,12 @@ func existsIn(pod corev1.Pod) bool {
 			return true
 		}
 	}
+	// NOTE: we also check init containers (native sidecars) since k8s 1.28.
+	// This should have no side effects.
+	for _, container := range pod.Spec.InitContainers {
+		if container.Name == naming.Container() {
+			return true
+		}
+	}
 	return false
 }

pkg/sidecar/pod_test.go

@@ -19,17 +19,114 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	colfeaturegate "go.opentelemetry.io/collector/featuregate"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	logf "sigs.k8s.io/controller-runtime/pkg/log"
 
 	"github.com/open-telemetry/opentelemetry-operator/apis/v1beta1"
 	"github.com/open-telemetry/opentelemetry-operator/internal/config"
 	"github.com/open-telemetry/opentelemetry-operator/internal/naming"
+	"github.com/open-telemetry/opentelemetry-operator/pkg/featuregate"
 )
 
 var logger = logf.Log.WithName("unit-tests")
 
+func sidecarFeatureGate(t *testing.T) {
+	originalVal := featuregate.EnableNativeSidecarContainers.IsEnabled()
+	t.Logf("original is: %+v", originalVal)
+	require.NoError(t, colfeaturegate.GlobalRegistry().Set(featuregate.EnableNativeSidecarContainers.ID(), true))
+	t.Cleanup(func() {
+		require.NoError(t, colfeaturegate.GlobalRegistry().Set(featuregate.EnableNativeSidecarContainers.ID(), originalVal))
+	})
+}
+
+func TestAddNativeSidecar(t *testing.T) {
+	sidecarFeatureGate(t)
+	// prepare
+	pod := corev1.Pod{
+		Spec: corev1.PodSpec{
+			Containers: []corev1.Container{
+				{Name: "my-app"},
+			},
+			InitContainers: []corev1.Container{
+				{
+					Name: "my-init",
+				},
+			},
+			// cross-test: the pod has a volume already, make sure we don't remove it
+			Volumes: []corev1.Volume{{}},
+		},
+	}
+
+	otelcol := v1beta1.OpenTelemetryCollector{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "otelcol-native-sidecar",
+			Namespace: "some-app",
+		},
+		Spec: v1beta1.OpenTelemetryCollectorSpec{
+			Mode: v1beta1.ModeSidecar,
+			OpenTelemetryCommonFields: v1beta1.OpenTelemetryCommonFields{
+				Ports: []corev1.ServicePort{
+					{
+						Name:     "metrics",
+						Port:     8888,
+						Protocol: corev1.ProtocolTCP,
+					},
+				},
+				InitContainers: []corev1.Container{
+					{
+						Name: "test",
+					},
+				},
+			},
+		},
+	}
+
+	otelcolYaml, err := otelcol.Spec.Config.Yaml()
+	require.NoError(t, err)
+	cfg := config.New(config.WithCollectorImage("some-default-image"))
+
+	// test
+	changed, err := add(cfg, logger, otelcol, pod, nil)
+
+	// verify
+	assert.NoError(t, err)
+	require.Len(t, changed.Spec.Containers, 1)
+	require.Len(t, changed.Spec.InitContainers, 3)
+	require.Len(t, changed.Spec.Volumes, 1)
+	assert.Equal(t, "some-app.otelcol-native-sidecar",
+		changed.Labels["sidecar.opentelemetry.io/injected"])
+	expectedPolicy := corev1.ContainerRestartPolicyAlways
+	assert.Equal(t, corev1.Container{
+		Name:          "otc-container",
+		Image:         "some-default-image",
+		Args:          []string{"--config=env:OTEL_CONFIG"},
+		RestartPolicy: &expectedPolicy,
+		Env: []corev1.EnvVar{
+			{
+				Name: "POD_NAME",
+				ValueFrom: &corev1.EnvVarSource{
+					FieldRef: &corev1.ObjectFieldSelector{
+						FieldPath: "metadata.name",
+					},
+				},
+			},
+			{
+				Name:  "OTEL_CONFIG",
+				Value: string(otelcolYaml),
+			},
+		},
+		Ports: []corev1.ContainerPort{
+			{
+				Name:          "metrics",
+				ContainerPort: 8888,
+				Protocol:      corev1.ProtocolTCP,
+			},
+		},
+	}, changed.Spec.InitContainers[2])
+}
+
 func TestAddSidecarWhenNoSidecarExists(t *testing.T) {
 	// prepare
 	pod := corev1.Pod{
@@ -144,6 +241,11 @@ func TestRemoveSidecar(t *testing.T) {
 				{Name: naming.Container()},
 				{Name: naming.Container()}, // two sidecars! should remove both
 			},
+			InitContainers: []corev1.Container{
+				{Name: "something"},
+				{Name: naming.Container()}, // NOTE: native sidecar since k8s 1.28.
+				{Name: naming.Container()}, // two sidecars! should remove both
+			},
 		},
 	}
 
@@ -190,6 +292,19 @@ func TestExistsIn(t *testing.T) {
 			},
 			true},
 
+		{"does-have-native-sidecar",
+			corev1.Pod{
+				Spec: corev1.PodSpec{
+					Containers: []corev1.Container{
+						{Name: "my-app"},
+					},
+					InitContainers: []corev1.Container{
+						{Name: naming.Container()},
+					},
+				},
+			},
+			true},
+
 		{"does-not-have-sidecar",
 			corev1.Pod{
 				Spec: corev1.PodSpec{