feat: allow engine args through VLLM_ and checks the engine args

src/engine_args.py

@@ -1,6 +1,7 @@
 import os
 import json
 import logging
+from typing import get_origin, get_args
 from torch.cuda import device_count
 from vllm import AsyncEngineArgs
 from vllm.model_executor.model_loader.tensorizer import TensorizerConfig
@@ -13,6 +14,96 @@ RENAME_ARGS_MAP = {
     "MAX_CONTEXT_LEN_TO_CAPTURE": "max_seq_len_to_capture"
 }
 
+VLLM_ENV_PREFIX = "VLLM_"
+
+
+def _resolve_field_type(field_type: type) -> type:
+    """Resolve Optional/Union to the concrete type for conversion."""
+    origin = get_origin(field_type)
+    args = get_args(field_type) if hasattr(field_type, "__args__") else ()
+    if origin is not None:
+        # Optional[X] is Union[X, None]; X | None is UnionType
+        non_none = [a for a in args if a is not type(None)]
+        if non_none:
+            return non_none[0]
+    return field_type
+
+
+def _convert_env_value_to_field_type(value: str, field_name: str, field_type: type):
+    """Convert env var string to the type expected by AsyncEngineArgs for this field."""
+    val = value.strip() if isinstance(value, str) else value
+    if val in ("", "None", "none"):
+        args = get_args(field_type) if hasattr(field_type, "__args__") else ()
+        if type(None) in (args or ()):
+            return None
+        raise ValueError("empty value not allowed for non-optional field")
+    effective_type = _resolve_field_type(field_type)
+    # bool
+    if effective_type is bool:
+        return str(val).lower() in ("true", "1", "yes", "on")
+    # int
+    if effective_type is int:
+        return int(val)
+    # float
+    if effective_type is float:
+        return float(val)
+    # str
+    if effective_type is str:
+        return str(val)
+    # dict, list, or complex (try JSON)
+    origin = get_origin(effective_type)
+    if effective_type in (dict, list) or origin in (dict, list):
+        try:
+            return json.loads(val)
+        except json.JSONDecodeError:
+            return val
+    # Fallback: try int, float, then str
+    try:
+        return int(val)
+    except ValueError:
+        pass
+    try:
+        return float(val)
+    except ValueError:
+        pass
+    return str(val)
+
+
+def _get_vllm_env_overrides() -> dict:
+    """Collect engine arg overrides from env vars with prefix VLLM_.
+
+    Any env var VLLM_<ARG> maps to the engine arg <arg> (lowercase).
+    E.g. VLLM_MAX_MODEL_LEN=4096 -> max_model_len=4096.
+    Only keys that exist on AsyncEngineArgs are applied; values are
+    converted to the field type (int, float, bool, str, json for dict/list).
+    """
+    overrides = {}
+    valid_fields = AsyncEngineArgs.__dataclass_fields__
+    for key, value in os.environ.items():
+        if not key.startswith(VLLM_ENV_PREFIX) or len(key) <= len(VLLM_ENV_PREFIX):
+            continue
+        suffix = key[len(VLLM_ENV_PREFIX) :]
+        arg_name = suffix.lower()
+        if arg_name not in valid_fields:
+            continue
+        field = valid_fields[arg_name]
+        try:
+            overrides[arg_name] = _convert_env_value_to_field_type(
+                value, arg_name, field.type
+            )
+        except (ValueError, TypeError, json.JSONDecodeError) as e:
+            logging.warning(
+                "Skip VLLM_ env override %s=%r: %s", key, value, e
+            )
+            continue
+    if overrides:
+        logging.info(
+            "Applying engine arg overrides from VLLM_ env vars: %s",
+            list(overrides.keys()),
+        )
+    return overrides
+
+
 DEFAULT_ARGS = {
     "disable_log_stats": os.getenv('DISABLE_LOG_STATS', 'False').lower() == 'true',
     # disable_log_requests is deprecated, use enable_log_requests instead
@@ -268,6 +359,9 @@ def get_engine_args():
     # Rename and match to vllm args
     args = match_vllm_args(args)
 
+    # Apply any VLLM_* env vars as overrides (e.g. VLLM_MAX_MODEL_LEN=4096 -> max_model_len=4096)
+    args.update(_get_vllm_env_overrides())
+
     if args.get("load_format") == "bitsandbytes":
         args["quantization"] = args["load_format"]