[Feature] specify model in config.yaml (#15798)

Signed-off-by: weizeng <weizeng@roblox.com>

docs/source/serving/openai_compatible_server.md

@@ -188,6 +188,7 @@ For example:
 ```yaml
 # config.yaml
 
+model: meta-llama/Llama-3.1-8B-Instruct
 host: "127.0.0.1"
 port: 6379
 uvicorn-log-level: "info"
@@ -196,12 +197,13 @@ uvicorn-log-level: "info"
 To use the above config file:
 
 ```bash
-vllm serve SOME_MODEL --config config.yaml
+vllm serve --config config.yaml
 ```
 
 :::{note}
 In case an argument is supplied simultaneously using command line and the config file, the value from the command line will take precedence.
 The order of priorities is `command line > config file values > defaults`.
+e.g. `vllm serve SOME_MODEL --config config.yaml`, SOME_MODEL takes precedence over `model` in config file.
 :::
 
 ## API Reference

tests/config/test_config_with_model.yaml

+# Same as test_config.yaml but with model specified
+model: config-model
+port: 12312
+served_model_name: mymodel
+tensor_parallel_size: 2
+trust_remote_code: true
+multi_step_stream_outputs: false

tests/conftest.py

@@ -1117,3 +1117,15 @@ def pytest_collection_modifyitems(config, items):
     for item in items:
         if "optional" in item.keywords:
             item.add_marker(skip_optional)
+
+
+@pytest.fixture(scope="session")
+def cli_config_file():
+    """Return the path to the CLI config file."""
+    return os.path.join(_TEST_DIR, "config", "test_config.yaml")
+
+
+@pytest.fixture(scope="session")
+def cli_config_file_with_model():
+    """Return the path to the CLI config file with model."""
+    return os.path.join(_TEST_DIR, "config", "test_config_with_model.yaml")

tests/test_utils.py

@@ -10,7 +10,7 @@ from unittest.mock import patch
 
 import pytest
 import torch
-from vllm_test_utils import monitor
+from vllm_test_utils.monitor import monitor
 
 from vllm.config import ParallelConfig, VllmConfig, set_current_vllm_config
 from vllm.utils import (FlexibleArgumentParser, MemorySnapshot,
@@ -143,7 +143,8 @@ def parser():
 def parser_with_config():
     parser = FlexibleArgumentParser()
     parser.add_argument('serve')
-    parser.add_argument('model_tag')
+    parser.add_argument('model_tag', nargs='?')
+    parser.add_argument('--model', type=str)
     parser.add_argument('--served-model-name', type=str)
     parser.add_argument('--config', type=str)
     parser.add_argument('--port', type=int)
@@ -199,29 +200,29 @@ def test_missing_required_argument(parser):
         parser.parse_args([])
 
 
-def test_cli_override_to_config(parser_with_config):
+def test_cli_override_to_config(parser_with_config, cli_config_file):
     args = parser_with_config.parse_args([
-        'serve', 'mymodel', '--config', './data/test_config.yaml',
+        'serve', 'mymodel', '--config', cli_config_file,
         '--tensor-parallel-size', '3'
     ])
     assert args.tensor_parallel_size == 3
     args = parser_with_config.parse_args([
         'serve', 'mymodel', '--tensor-parallel-size', '3', '--config',
-        './data/test_config.yaml'
+        cli_config_file
     ])
     assert args.tensor_parallel_size == 3
     assert args.port == 12312
     args = parser_with_config.parse_args([
         'serve', 'mymodel', '--tensor-parallel-size', '3', '--config',
-        './data/test_config.yaml', '--port', '666'
+        cli_config_file, '--port', '666'
     ])
     assert args.tensor_parallel_size == 3
     assert args.port == 666
 
 
-def test_config_args(parser_with_config):
+def test_config_args(parser_with_config, cli_config_file):
     args = parser_with_config.parse_args(
-        ['serve', 'mymodel', '--config', './data/test_config.yaml'])
+        ['serve', 'mymodel', '--config', cli_config_file])
     assert args.tensor_parallel_size == 2
     assert args.trust_remote_code
     assert not args.multi_step_stream_outputs
@@ -243,10 +244,9 @@ def test_config_file(parser_with_config):
         ])
 
 
-def test_no_model_tag(parser_with_config):
+def test_no_model_tag(parser_with_config, cli_config_file):
     with pytest.raises(ValueError):
-        parser_with_config.parse_args(
-            ['serve', '--config', './data/test_config.yaml'])
+        parser_with_config.parse_args(['serve', '--config', cli_config_file])
 
 
 # yapf: enable
@@ -480,6 +480,48 @@ def test_swap_dict_values(obj, key1, key2):
     else:
         assert key1 not in obj
 
+
+def test_model_specification(parser_with_config,
+                             cli_config_file,
+                             cli_config_file_with_model):
+    # Test model in CLI takes precedence over config
+    args = parser_with_config.parse_args([
+        'serve', 'cli-model', '--config', cli_config_file_with_model
+    ])
+    assert args.model_tag == 'cli-model'
+    assert args.served_model_name == 'mymodel'
+
+    # Test model from config file works
+    args = parser_with_config.parse_args([
+        'serve', '--config', cli_config_file_with_model,
+    ])
+    assert args.model == 'config-model'
+    assert args.served_model_name == 'mymodel'
+
+    # Test no model specified anywhere raises error
+    with pytest.raises(ValueError, match="No model specified!"):
+        parser_with_config.parse_args(['serve', '--config', cli_config_file])
+
+    # Test using --model option raises error
+    with pytest.raises(
+        ValueError,
+        match=(
+            "With `vllm serve`, you should provide the model as a positional "
+            "argument or in a config file instead of via the `--model` option."
+        ),
+    ):
+        parser_with_config.parse_args(['serve', '--model', 'my-model'])
+
+    # Test other config values are preserved
+    args = parser_with_config.parse_args([
+        'serve', 'cli-model', '--config', cli_config_file_with_model,
+    ])
+    assert args.tensor_parallel_size == 2
+    assert args.trust_remote_code is True
+    assert args.multi_step_stream_outputs is False
+    assert args.port == 12312
+
+
 @pytest.mark.parametrize("input", [(), ("abc", ), (None, ),
                                     (None, bool, [1, 2, 3])])
 @pytest.mark.parametrize("output", [0, 1, 2])

vllm/entrypoints/cli/serve.py

@@ -4,7 +4,6 @@ import argparse
 
 import uvloop
 
-from vllm.engine.arg_utils import EngineArgs
 from vllm.entrypoints.cli.types import CLISubcommand
 from vllm.entrypoints.openai.api_server import run_server
 from vllm.entrypoints.openai.cli_args import (make_arg_parser,
@@ -21,14 +20,9 @@ class ServeSubcommand(CLISubcommand):
 
     @staticmethod
     def cmd(args: argparse.Namespace) -> None:
-        # The default value of `--model`
-        if args.model != EngineArgs.model:
-            raise ValueError(
-                "With `vllm serve`, you should provide the model as a "
-                "positional argument instead of via the `--model` option.")
-
-        # EngineArgs expects the model name to be passed as --model.
-        args.model = args.model_tag
+        # If model is specified in CLI (as positional arg), it takes precedence
+        if hasattr(args, 'model_tag') and args.model_tag is not None:
+            args.model = args.model_tag
 
         uvloop.run(run_server(args))
 
@@ -41,10 +35,12 @@ class ServeSubcommand(CLISubcommand):
         serve_parser = subparsers.add_parser(
             "serve",
             help="Start the vLLM OpenAI Compatible API server",
-            usage="vllm serve <model_tag> [options]")
+            usage="vllm serve [model_tag] [options]")
         serve_parser.add_argument("model_tag",
                                   type=str,
-                                  help="The model tag to serve")
+                                  nargs='?',
+                                  help="The model tag to serve "
+                                  "(optional if specified in config)")
         serve_parser.add_argument(
             "--config",
             type=str,

vllm/utils.py

@@ -1241,6 +1241,16 @@ class FlexibleArgumentParser(argparse.ArgumentParser):
         if args is None:
             args = sys.argv[1:]
 
+        # Check for --model in command line arguments first
+        if args and args[0] == "serve":
+            model_in_cli_args = any(arg == '--model' for arg in args)
+
+            if model_in_cli_args:
+                raise ValueError(
+                    "With `vllm serve`, you should provide the model as a "
+                    "positional argument or in a config file instead of via "
+                    "the `--model` option.")
+
         if '--config' in args:
             args = self._pull_args_from_config(args)
 
@@ -1324,19 +1334,29 @@ class FlexibleArgumentParser(argparse.ArgumentParser):
         config_args = self._load_config_file(file_path)
 
         # 0th index is for {serve,chat,complete}
-        # followed by model_tag (only for serve)
+        # optionally followed by model_tag (only for serve)
         # followed by config args
         # followed by rest of cli args.
         # maintaining this order will enforce the precedence
         # of cli > config > defaults
         if args[0] == "serve":
-            if index == 1:
+            model_in_cli = len(args) > 1 and not args[1].startswith('-')
+            model_in_config = any(arg == '--model' for arg in config_args)
+
+            if not model_in_cli and not model_in_config:
                 raise ValueError(
-                    "No model_tag specified! Please check your command-line"
-                    " arguments.")
-            args = [args[0]] + [
-                args[1]
-            ] + config_args + args[2:index] + args[index + 2:]
+                    "No model specified! Please specify model either "
+                    "as a positional argument or in a config file.")
+
+            if model_in_cli:
+                # Model specified as positional arg, keep CLI version
+                args = [args[0]] + [
+                    args[1]
+                ] + config_args + args[2:index] + args[index + 2:]
+            else:
+                # No model in CLI, use config if available
+                args = [args[0]
+                        ] + config_args + args[1:index] + args[index + 2:]
         else:
             args = [args[0]] + config_args + args[1:index] + args[index + 2:]
 
@@ -1354,9 +1374,7 @@ class FlexibleArgumentParser(argparse.ArgumentParser):
                 '--port': '12323',
                 '--tensor-parallel-size': '4'
             ]
-
         """
-
         extension: str = file_path.split('.')[-1]
         if extension not in ('yaml', 'yml'):
             raise ValueError(