Fix/background health check (#10887)

* fix: improve health check logic by deep copying model list on each iteration

* test: add async test for background health check reflecting model list changes

* fix: validate health check interval before executing background health check

* fix: specify type for health check results dictionary

tests/proxy_unit_tests/test_proxy_server.py

@@ -2194,6 +2194,50 @@ async def test_get_ui_settings_spend_logs_threshold():
     proxy_state.set_proxy_state_variable("spend_logs_row_count", 0)
 
 
+@pytest.mark.asyncio
+async def test_run_background_health_check_reflects_llm_model_list(monkeypatch):
+    """
+    Test that _run_background_health_check reflects changes to llm_model_list in each health check iteration.
+    """
+    import litellm.proxy.proxy_server as proxy_server
+    import copy
+
+    test_model_list_1 = [{"model_name": "model-a"}]
+    test_model_list_2 = [{"model_name": "model-b"}]
+    called_model_lists = []
+
+    async def fake_perform_health_check(model_list, details):
+        called_model_lists.append(copy.deepcopy(model_list))
+        return (["healthy"], ["unhealthy"])
+
+    monkeypatch.setattr(proxy_server, "health_check_interval", 1)
+    monkeypatch.setattr(proxy_server, "health_check_details", None)
+    monkeypatch.setattr(proxy_server, "llm_model_list", copy.deepcopy(test_model_list_1))
+    monkeypatch.setattr(proxy_server, "perform_health_check", fake_perform_health_check)
+    monkeypatch.setattr(proxy_server, "health_check_results", {})
+
+    async def fake_sleep(interval):
+        raise asyncio.CancelledError()
+
+    monkeypatch.setattr(asyncio, "sleep", fake_sleep)
+
+    try:
+        await proxy_server._run_background_health_check()
+    except asyncio.CancelledError:
+        pass
+
+    monkeypatch.setattr(proxy_server, "llm_model_list", copy.deepcopy(test_model_list_2))
+
+    try:
+        await proxy_server._run_background_health_check()
+    except asyncio.CancelledError:
+        pass
+
+    assert len(called_model_lists) >= 2
+    assert called_model_lists[0] == test_model_list_1
+    assert called_model_lists[1] == test_model_list_2
+
+
 def test_get_timeout_from_request():
     from litellm.proxy.litellm_pre_call_utils import LiteLLMProxyRequestSetup