[Bugfix][Router] Remove ghost endpoint on evicted-worker MODIFIED event

src/tests/test_k8s_pod_ip_service_discovery.py

@@ -0,0 +1,127 @@
+"""Unit tests for K8sPodIPServiceDiscovery._on_engine_update.
+
+These tests focus on the pure event-handling logic of the pod-IP based
+service discovery, in particular the MODIFIED branch that removes a stale
+("ghost") endpoint when a pod's podIP is cleared by a node-pressure
+eviction.
+
+The real __init__ loads a kubeconfig and starts a watcher thread, so we
+construct the instance with __new__ and inject only the attributes that
+_on_engine_update touches.
+"""
+
+import threading
+from unittest.mock import MagicMock
+
+from vllm_router.service_discovery import EndpointInfo, K8sPodIPServiceDiscovery
+
+
+def _make_discovery() -> K8sPodIPServiceDiscovery:
+    d = K8sPodIPServiceDiscovery.__new__(K8sPodIPServiceDiscovery)
+    d.available_engines = {}
+    d.available_engines_lock = threading.Lock()
+    d.known_models = set()
+    d.known_models_lock = threading.Lock()
+    d.namespace = "test-ns"
+    d.port = "8000"
+    return d
+
+
+def _register(d: K8sPodIPServiceDiscovery, name: str) -> None:
+    d.available_engines[name] = MagicMock(spec=EndpointInfo)
+
+
+def test_modified_with_none_ip_removes_registered_engine():
+    """Core regression: an evicted pod delivers MODIFIED with podIP=None.
+
+    Before the fix this returned early and the endpoint lingered as a
+    ghost; after the fix the registered endpoint is removed.
+    """
+    d = _make_discovery()
+    _register(d, "pod-a")
+
+    d._on_engine_update(
+        engine_name="pod-a",
+        engine_ip=None,
+        event="MODIFIED",
+        is_pod_ready=False,
+        model_names=[],
+        model_label=None,
+    )
+
+    assert "pod-a" not in d.available_engines
+
+
+def test_modified_with_none_ip_unregistered_is_noop():
+    """A Pending pod (not yet registered) with no IP must be skipped, not error."""
+    d = _make_discovery()
+
+    d._on_engine_update(
+        engine_name="pending-pod",
+        engine_ip=None,
+        event="MODIFIED",
+        is_pod_ready=False,
+        model_names=[],
+        model_label=None,
+    )
+
+    assert d.available_engines == {}
+
+
+def test_added_with_none_ip_is_skipped():
+    """ADDED with no IP (Pending pod) must not register anything.
+
+    Confirms the ADDED branch is unchanged by the fix.
+    """
+    d = _make_discovery()
+    d._add_engine = MagicMock()
+
+    d._on_engine_update(
+        engine_name="pending-pod",
+        engine_ip=None,
+        event="ADDED",
+        is_pod_ready=False,
+        model_names=[],
+        model_label=None,
+    )
+
+    d._add_engine.assert_not_called()
+    assert d.available_engines == {}
+
+
+def test_modified_ready_with_ip_adds_engine():
+    """MODIFIED with a real IP + ready + models must (re)add the engine."""
+    d = _make_discovery()
+    d._add_engine = MagicMock()
+
+    d._on_engine_update(
+        engine_name="pod-b",
+        engine_ip="172.16.0.5",
+        event="MODIFIED",
+        is_pod_ready=True,
+        model_names=["Qwen2.5-7B"],
+        model_label="Qwen2.5-7B",
+    )
+
+    d._add_engine.assert_called_once_with(
+        "pod-b", "172.16.0.5", ["Qwen2.5-7B"], "Qwen2.5-7B"
+    )
+
+
+def test_modified_not_ready_with_ip_removes_registered():
+    """Graceful drain: a registered pod goes not-ready while its IP is still
+    present. The existing (pre-fix) removal path must still work.
+    """
+    d = _make_discovery()
+    _register(d, "pod-c")
+
+    d._on_engine_update(
+        engine_name="pod-c",
+        engine_ip="172.16.0.9",
+        event="MODIFIED",
+        is_pod_ready=False,
+        model_names=[],
+        model_label=None,
+    )
+
+    assert "pod-c" not in d.available_engines

src/vllm_router/service_discovery.py

@@ -806,6 +806,20 @@ def _on_engine_update(
 
         elif event == "MODIFIED":
             if engine_ip is None:
+                # An empty IP is ambiguous: a Pending pod has not been
+                # assigned an IP yet (skip it), but an Evicted pod has had
+                # its podIP cleared by the kubelet. In the latter case the
+                # endpoint is already registered and must be removed, or it
+                # lingers as a stale ("ghost") backend that still receives
+                # traffic until the router process restarts. Complete the
+                # symmetric removal path here.
+                if engine_name in self.available_engines:
+                    logger.warning(
+                        f"Serving engine {engine_name} has an empty IP "
+                        f"(likely evicted, podIP cleared by kubelet); "
+                        f"removing it to avoid a stale (ghost) endpoint"
+                    )
+                    self._delete_engine(engine_name)
                 return
 
             if is_pod_ready and model_names: