[k8sobserver] enable the observation of ingress objects (#35539)

**Description:** This PR fixes the observation of ingress objects by the
k8sobserver. The issue was that the `observe_ingresses` option was not
considered in the extension setup, and no informer for the ingress
resource type has been created

**Link to tracking Issue:** #35324 

**Testing:** Added unit tests. Also did manual testing against a k8s
cluster to check whether ingress objects are picked up as expected

**Documentation:** No change there, as the `observe_ingresses` option
was already documented in the readme

---------

Signed-off-by: Florian Bacher <florian.bacher@dynatrace.com>
Co-authored-by: Moritz Wiesinger <moritz.wiesinger@dynatrace.com>

.chloggen/k8s-observer-ingress.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: k8sobserver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Enable observation of ingress objects if the `ObserveIngresses` config option is set to true
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [35324]
+
+# (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:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

extension/observer/k8sobserver/extension.go

@@ -13,6 +13,7 @@ import (
 	"go.opentelemetry.io/collector/extension"
 	"go.uber.org/zap"
 	v1 "k8s.io/api/core/v1"
+	networkingv1 "k8s.io/api/networking/v1"
 	"k8s.io/apimachinery/pkg/fields"
 	"k8s.io/client-go/tools/cache"
 
@@ -29,6 +30,7 @@ type k8sObserver struct {
 	podListerWatcher     cache.ListerWatcher
 	serviceListerWatcher cache.ListerWatcher
 	nodeListerWatcher    cache.ListerWatcher
+	ingressListerWatcher cache.ListerWatcher
 	handler              *handler
 	once                 *sync.Once
 	stop                 chan struct{}
@@ -69,6 +71,14 @@ func (k *k8sObserver) Start(_ context.Context, _ component.Host) error {
 				k.telemetry.Logger.Error("error adding event handler to node informer", zap.Error(err))
 			}
 		}
+		if k.ingressListerWatcher != nil {
+			k.telemetry.Logger.Debug("creating and starting ingress informer")
+			ingressInformer := cache.NewSharedInformer(k.ingressListerWatcher, &networkingv1.Ingress{}, 0)
+			go ingressInformer.Run(k.stop)
+			if _, err := ingressInformer.AddEventHandler(k.handler); err != nil {
+				k.telemetry.Logger.Error("error adding event handler to ingress informer", zap.Error(err))
+			}
+		}
 	})
 	return nil
 }
@@ -117,13 +127,21 @@ func newObserver(config *Config, set extension.Settings) (extension.Extension, e
 		set.Logger.Debug("observing nodes")
 		nodeListerWatcher = cache.NewListWatchFromClient(restClient, "nodes", v1.NamespaceAll, nodeSelector)
 	}
+
+	var ingressListerWatcher cache.ListerWatcher
+	if config.ObserveIngresses {
+		var ingressSelector = fields.Everything()
+		set.Logger.Debug("observing ingresses")
+		ingressListerWatcher = cache.NewListWatchFromClient(client.NetworkingV1().RESTClient(), "ingresses", v1.NamespaceAll, ingressSelector)
+	}
 	h := &handler{idNamespace: set.ID.String(), endpoints: &sync.Map{}, logger: set.TelemetrySettings.Logger}
 	obs := &k8sObserver{
 		EndpointsWatcher:     observer.NewEndpointsWatcher(h, time.Second, set.TelemetrySettings.Logger),
 		telemetry:            set.TelemetrySettings,
 		podListerWatcher:     podListerWatcher,
 		serviceListerWatcher: serviceListerWatcher,
 		nodeListerWatcher:    nodeListerWatcher,
+		ingressListerWatcher: ingressListerWatcher,
 		stop:                 make(chan struct{}),
 		config:               config,
 		handler:              h,

extension/observer/k8sobserver/extension_test.go

@@ -312,3 +312,88 @@ func TestExtensionObserveNodes(t *testing.T) {
 	require.NoError(t, ext.Shutdown(context.Background()))
 	obs.StopListAndWatch()
 }
+
+func TestExtensionObserveIngresses(t *testing.T) {
+	factory := NewFactory()
+	config := factory.CreateDefaultConfig().(*Config)
+	config.ObservePods = false // avoid causing data race when multiple test cases running in the same process using podListerWatcher
+	config.ObserveIngresses = true
+	mockServiceHost(t, config)
+
+	set := extensiontest.NewNopSettings()
+	set.ID = component.NewID(metadata.Type)
+	ext, err := newObserver(config, set)
+	require.NoError(t, err)
+	require.NotNil(t, ext)
+
+	obs := ext.(*k8sObserver)
+	ingressListerWatcher := framework.NewFakeControllerSource()
+	obs.ingressListerWatcher = ingressListerWatcher
+
+	ingressListerWatcher.Add(ingress)
+
+	require.NoError(t, ext.Start(context.Background(), componenttest.NewNopHost()))
+
+	sink := &endpointSink{}
+	obs.ListAndWatch(sink)
+
+	requireSink(t, sink, func() bool {
+		return len(sink.added) == 1
+	})
+
+	assert.Equal(t, observer.Endpoint{
+		ID:     "k8s_observer/ingress-1-UID/host-1/",
+		Target: "https://host-1/",
+		Details: &observer.K8sIngress{
+			Name:      "application-ingress",
+			UID:       "k8s_observer/ingress-1-UID/host-1/",
+			Labels:    map[string]string{"env": "prod"},
+			Namespace: "default",
+			Scheme:    "https",
+			Host:      "host-1",
+			Path:      "/",
+		},
+	}, sink.added[0])
+
+	ingressListerWatcher.Modify(ingressV2)
+
+	requireSink(t, sink, func() bool {
+		return len(sink.changed) == 1
+	})
+
+	assert.Equal(t, observer.Endpoint{
+		ID:     "k8s_observer/ingress-1-UID/host-1/",
+		Target: "https://host-1/",
+		Details: &observer.K8sIngress{
+			Name:      "application-ingress",
+			UID:       "k8s_observer/ingress-1-UID/host-1/",
+			Labels:    map[string]string{"env": "hardening"},
+			Namespace: "default",
+			Scheme:    "https",
+			Host:      "host-1",
+			Path:      "/",
+		},
+	}, sink.changed[0])
+
+	ingressListerWatcher.Delete(ingressV2)
+
+	requireSink(t, sink, func() bool {
+		return len(sink.removed) == 1
+	})
+
+	assert.Equal(t, observer.Endpoint{
+		ID:     "k8s_observer/ingress-1-UID/host-1/",
+		Target: "https://host-1/",
+		Details: &observer.K8sIngress{
+			Name:      "application-ingress",
+			UID:       "k8s_observer/ingress-1-UID/host-1/",
+			Labels:    map[string]string{"env": "hardening"},
+			Namespace: "default",
+			Scheme:    "https",
+			Host:      "host-1",
+			Path:      "/",
+		},
+	}, sink.removed[0])
+
+	require.NoError(t, ext.Shutdown(context.Background()))
+}

extension/observer/k8sobserver/k8s_fixtures_test.go

@@ -168,6 +168,12 @@ var ingress = &networkingv1.Ingress{
 	},
 }
 
+var ingressV2 = func() *networkingv1.Ingress {
+	i2 := ingress.DeepCopy()
+	i2.Labels["env"] = "hardening"
+	return i2
+}()
+
 var ingressMultipleHost = &networkingv1.Ingress{
 	ObjectMeta: metav1.ObjectMeta{
 		Namespace: "default",