[feature] Enable injecting only core SDK config

Closes #990.

Adds support for injecting SDK environment variables only,
without injecting language-specific libraries or config.

Usage:

```bash
instrumentation.opentelemetry.io/inject-sdk: "true"
```

README.md

@@ -210,6 +210,11 @@ Python:
 instrumentation.opentelemetry.io/inject-python: "true"
 ```
 
+OpenTelemetry SDK environment variables only:
+```bash
+instrumentation.opentelemetry.io/inject-sdk: "true"
+```
+
 The possible values for the annotation can be
 * `"true"` - inject and `Instrumentation` resource from the namespace.
 * `"my-instrumentation"` - name of `Instrumentation` CR instance in the current namespace.
@@ -273,9 +278,17 @@ spec:
     image: your-customized-auto-instrumentation-image:python
 ```
 
-The Dockerfiles for auto-instrumentation can be found in [autoinstrumentation directory](./autoinstrumentation). 
+The Dockerfiles for auto-instrumentation can be found in [autoinstrumentation directory](./autoinstrumentation).
 Follow the instructions in the Dockerfiles on how to build a custom container image.
 
+#### Inject OpenTelemetry SDK environment variables only
+
+You can configure the OpenTelemetry SDK for applications which can't currently be autoinstrumented by using `inject-sdk` in place of (e.g.) `inject-python` or `inject-java`. This will inject environment variables like `OTEL_RESOURCE_ATTRIBUTES`, `OTEL_TRACES_SAMPLER`, and `OTEL_EXPORTER_OTLP_ENDPOINT`, that you can configure in the `Instrumentation`, but will not actually provide the SDK.
+
+```bash
+instrumentation.opentelemetry.io/inject-sdk: "true"
+```
+
 ## Compatibility matrix
 
 ### OpenTelemetry Operator vs. OpenTelemetry Collector

pkg/instrumentation/annotation.go

@@ -26,6 +26,7 @@ const (
 	annotationInjectJava          = "instrumentation.opentelemetry.io/inject-java"
 	annotationInjectNodeJS        = "instrumentation.opentelemetry.io/inject-nodejs"
 	annotationInjectPython        = "instrumentation.opentelemetry.io/inject-python"
+	annotationInjectSdk           = "instrumentation.opentelemetry.io/inject-sdk"
 	annotationInjectContainerName = "instrumentation.opentelemetry.io/container-names"
 )
 

pkg/instrumentation/podmutator.go

@@ -43,6 +43,7 @@ type languageInstrumentations struct {
 	Java   *v1alpha1.Instrumentation
 	NodeJS *v1alpha1.Instrumentation
 	Python *v1alpha1.Instrumentation
+	Sdk    *v1alpha1.Instrumentation
 }
 
 var _ webhookhandler.PodMutator = (*instPodMutator)(nil)
@@ -95,7 +96,14 @@ func (pm *instPodMutator) Mutate(ctx context.Context, ns corev1.Namespace, pod c
 	}
 	insts.Python = inst
 
-	if insts.Java == nil && insts.NodeJS == nil && insts.Python == nil {
+	if inst, err = pm.getInstrumentationInstance(ctx, ns, pod, annotationInjectSdk); err != nil {
+		// we still allow the pod to be created, but we log a message to the operator's logs
+		logger.Error(err, "failed to select an OpenTelemetry Instrumentation instance for this pod")
+		return pod, err
+	}
+	insts.Sdk = inst
+
+	if insts.Java == nil && insts.NodeJS == nil && insts.Python == nil && insts.Sdk == nil {
 		logger.V(1).Info("annotation not present in deployment, skipping instrumentation injection")
 		return pod, nil
 	}

pkg/instrumentation/sdk.go

@@ -83,6 +83,12 @@ func (i *sdkInjector) inject(ctx context.Context, insts languageInstrumentations
 		pod = i.injectCommonEnvVar(otelinst, pod, index)
 		pod = i.injectCommonSDKConfig(ctx, otelinst, ns, pod, index)
 	}
+	if insts.Sdk != nil {
+		otelinst := *insts.Sdk
+		i.logger.V(1).Info("injecting sdk-only instrumentation into pod", "otelinst-namespace", otelinst.Namespace, "otelinst-name", otelinst.Name)
+		pod = i.injectCommonEnvVar(otelinst, pod, index)
+		pod = i.injectCommonSDKConfig(ctx, otelinst, ns, pod, index)
+	}
 	return pod
 }
 

pkg/instrumentation/sdk_test.go

@@ -670,3 +670,70 @@ func TestInjectPython(t *testing.T) {
 		},
 	}, pod)
 }
+
+func TestInjectSdkOnly(t *testing.T) {
+	inst := v1alpha1.Instrumentation{
+		Spec: v1alpha1.InstrumentationSpec{
+			Exporter: v1alpha1.Exporter{
+				Endpoint: "https://collector:4318",
+			},
+		},
+	}
+	insts := languageInstrumentations{
+		Sdk: &inst,
+	}
+
+	inj := sdkInjector{
+		logger: logr.Discard(),
+	}
+	pod := inj.inject(context.Background(), insts,
+		corev1.Namespace{},
+		corev1.Pod{
+			Spec: corev1.PodSpec{
+				Containers: []corev1.Container{
+					{
+						Name: "app",
+					},
+				},
+			},
+		}, "")
+	assert.Equal(t, corev1.Pod{
+		Spec: corev1.PodSpec{
+			Containers: []corev1.Container{
+				{
+					Name: "app",
+					Env: []corev1.EnvVar{
+						{
+							Name:  "OTEL_SERVICE_NAME",
+							Value: "app",
+						},
+						{
+							Name:  "OTEL_EXPORTER_OTLP_ENDPOINT",
+							Value: "https://collector:4318",
+						},
+						{
+							Name: "OTEL_RESOURCE_ATTRIBUTES_POD_NAME",
+							ValueFrom: &corev1.EnvVarSource{
+								FieldRef: &corev1.ObjectFieldSelector{
+									FieldPath: "metadata.name",
+								},
+							},
+						},
+						{
+							Name: "OTEL_RESOURCE_ATTRIBUTES_NODE_NAME",
+							ValueFrom: &corev1.EnvVarSource{
+								FieldRef: &corev1.ObjectFieldSelector{
+									FieldPath: "spec.nodeName",
+								},
+							},
+						},
+						{
+							Name:  "OTEL_RESOURCE_ATTRIBUTES",
+							Value: "k8s.container.name=app,k8s.node.name=$(OTEL_RESOURCE_ATTRIBUTES_NODE_NAME),k8s.pod.name=$(OTEL_RESOURCE_ATTRIBUTES_POD_NAME)",
+						},
+					},
+				},
+			},
+		},
+	}, pod)
+}

tests/e2e/instrumentation-sdk/00-install-collector.yaml

@@ -0,0 +1,23 @@
+apiVersion: opentelemetry.io/v1alpha1
+kind: OpenTelemetryCollector
+metadata:
+  name: sidecar
+spec:
+  mode: sidecar
+  config: |
+    receivers:
+      otlp:
+        protocols:
+          grpc:
+          http:
+    processors:
+
+    exporters:
+      logging:
+
+    service:
+      pipelines:
+        traces:
+          receivers: [otlp]
+          processors: []
+          exporters: [logging]

tests/e2e/instrumentation-sdk/00-install-instrumentation.yaml

@@ -0,0 +1,24 @@
+apiVersion: opentelemetry.io/v1alpha1
+kind: Instrumentation
+metadata:
+  name: sdk-only
+spec:
+  env:
+    - name: SPLUNK_TRACE_RESPONSE_HEADER_ENABLED
+      value: "true"
+  exporter:
+    endpoint: http://localhost:4317
+  propagators:
+    - jaeger
+    - b3
+  sampler:
+    type: parentbased_traceidratio
+    argument: "0.25"
+  nodejs:
+    env:
+      - name: OTEL_NODEJS_DEBUG
+        value: "true"
+  python:
+    env:
+      - name: OTEL_ENV_VAR
+        value: "true"

tests/e2e/instrumentation-sdk/01-assert.yaml

@@ -0,0 +1,27 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  annotations:
+    sidecar.opentelemetry.io/inject: "true"
+    instrumentation.opentelemetry.io/inject-sdk: "true"
+  labels:
+    app: my-pod-with-sidecar
+spec:
+  containers:
+  - name: myapp
+    env:
+    - name: SPLUNK_TRACE_RESPONSE_HEADER_ENABLED
+      value: "true"
+    - name: OTEL_SERVICE_NAME
+    - name: OTEL_EXPORTER_OTLP_ENDPOINT
+      value: http://localhost:4317
+    - name: OTEL_RESOURCE_ATTRIBUTES_POD_NAME
+    - name: OTEL_RESOURCE_ATTRIBUTES_NODE_NAME
+    - name: OTEL_PROPAGATORS
+      value: jaeger,b3
+    - name: OTEL_TRACES_SAMPLER
+    - name: OTEL_TRACES_SAMPLER_ARG
+    - name: OTEL_RESOURCE_ATTRIBUTES
+  - name: otc-container
+status:
+  phase: Running

tests/e2e/instrumentation-sdk/01-install-app.yaml

@@ -0,0 +1,24 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: my-deployment-with-sidecar
+spec:
+  selector:
+    matchLabels:
+      app: my-pod-with-sidecar
+  replicas: 1
+  template:
+    metadata:
+      labels:
+        app: my-pod-with-sidecar
+      annotations:
+        sidecar.opentelemetry.io/inject: "true"
+        instrumentation.opentelemetry.io/inject-sdk: "true"
+    spec:
+      securityContext:
+        runAsUser: 1000
+        runAsGroup: 3000
+        fsGroup: 2000
+      containers:
+      - name: myapp
+        image: ghcr.io/anuraaga/express-hello-world:latest