[Core] Raise when non-multi-instance DP clients target a DP rank (#19227)

Signed-off-by: Jon Swenson <jmswen@gmail.com>

tests/async_engine/test_async_llm_engine.py

@@ -384,3 +384,25 @@ async def test_delayed_generator(async_engine, stop):
     assert final_output is not None
     assert len(final_output.outputs[0].token_ids) == 10
     assert final_output.finished
+
+
+@pytest.mark.asyncio(scope="module")
+async def test_invalid_argument(async_engine):
+    scheduler_config = await async_engine.get_scheduler_config()
+
+    if scheduler_config.num_scheduler_steps != 1:
+        pytest.skip("no need to test this one with multistep")
+
+    sampling_params = SamplingParams(
+        temperature=0,
+        min_tokens=10,
+        max_tokens=10,
+    )
+
+    # Targeting specific DP rank only supported in v1 multi-instance DP
+    with pytest.raises(ValueError):
+        async for _ in async_engine.generate("test",
+                                             sampling_params,
+                                             request_id=uid(),
+                                             data_parallel_rank=0):
+            pass