[Frontend]-config-cli-args (#7737)

Co-authored-by: Cyrus Leung <cyrus.tl.leung@gmail.com>
Co-authored-by: Kaunil Dhruv <kaunil_dhruv@intuit.com>

vllm/utils.py

@@ -25,6 +25,7 @@ import numpy.typing as npt
 import psutil
 import torch
 import torch.types
+import yaml
 from packaging.version import Version
 from typing_extensions import ParamSpec, TypeIs, assert_never
 
@@ -1093,6 +1094,9 @@ class FlexibleArgumentParser(argparse.ArgumentParser):
         if args is None:
             args = sys.argv[1:]
 
+        if '--config' in args:
+            args = FlexibleArgumentParser._pull_args_from_config(args)
+
         # Convert underscores to dashes and vice versa in argument names
         processed_args = []
         for arg in args:
@@ -1109,6 +1113,103 @@ class FlexibleArgumentParser(argparse.ArgumentParser):
 
         return super().parse_args(processed_args, namespace)
 
+    @staticmethod
+    def _pull_args_from_config(args: List[str]) -> List[str]:
+        """Method to pull arguments specified in the config file
+        into the command-line args variable.
+        
+        The arguments in config file will be inserted between 
+        the argument list.
+        
+        example:
+        ```yaml
+            port: 12323
+            tensor-parallel-size: 4
+        ```
+        ```python
+        $: vllm {serve,chat,complete} "facebook/opt-12B" \
+            --config config.yaml -tp 2
+        $: args = [
+            "serve,chat,complete",
+            "facebook/opt-12B", 
+            '--config', 'config.yaml', 
+            '-tp', '2'
+        ]
+        $: args = [
+            "serve,chat,complete",
+            "facebook/opt-12B", 
+            '--port', '12323', 
+            '--tensor-parallel-size', '4', 
+            '-tp', '2'
+            ]
+        ```
+
+        Please note how the config args are inserted after the sub command.
+        this way the order of priorities is maintained when these are args 
+        parsed by super().
+        """
+        assert args.count(
+            '--config') <= 1, "More than one config file specified!"
+
+        index = args.index('--config')
+        if index == len(args) - 1:
+            raise ValueError("No config file specified! \
+                             Please check your command-line arguments.")
+
+        file_path = args[index + 1]
+
+        config_args = FlexibleArgumentParser._load_config_file(file_path)
+
+        # 0th index is for {serve,chat,complete}
+        # followed by config args
+        # followed by rest of cli args.
+        # maintaining this order will enforce the precedence
+        # of cli > config > defaults
+        args = [args[0]] + config_args + args[1:index] + args[index + 2:]
+
+        return args
+
+    @staticmethod
+    def _load_config_file(file_path: str) -> List[str]:
+        """Loads a yaml file and returns the key value pairs as a 
+        flattened list with argparse like pattern
+        ```yaml
+            port: 12323
+            tensor-parallel-size: 4
+        ```
+        returns:
+            processed_args: list[str] = [
+                '--port': '12323',
+                '--tensor-parallel-size': '4'
+            ]
+        
+        """
+
+        extension: str = file_path.split('.')[-1]
+        if extension not in ('yaml', 'yml'):
+            raise ValueError(
+                "Config file must be of a yaml/yml type.\
+                              %s supplied", extension)
+
+        # only expecting a flat dictionary of atomic types
+        processed_args: List[str] = []
+
+        config: Dict[str, Union[int, str]] = {}
+        try:
+            with open(file_path, 'r') as config_file:
+                config = yaml.safe_load(config_file)
+        except Exception as ex:
+            logger.error(
+                "Unable to read the config file at %s. \
+                Make sure path is correct", file_path)
+            raise ex
+
+        for key, value in config.items():
+            processed_args.append('--' + key)
+            processed_args.append(str(value))
+
+        return processed_args
+
 
 async def _run_task_with_lock(task: Callable, lock: asyncio.Lock, *args,
                               **kwargs):