[PD] Support get_model_info interface for mini_lb (#9792)

Signed-off-by: Xuchun Shang <xuchun.shang@linux.alibaba.com>
Co-authored-by: Teng Ma <sima.mt@alibaba-inc.com>

python/sglang/srt/disaggregation/mini_lb.py

@@ -7,6 +7,7 @@ import dataclasses
 import logging
 import random
 import urllib
+from http import HTTPStatus
 from itertools import chain
 from typing import List, Optional
 
@@ -262,14 +263,38 @@ async def get_server_info():
 
 @app.get("/get_model_info")
 async def get_model_info():
-    # Dummy model information
-    model_info = {
-        "model_path": "/path/to/dummy/model",
-        "tokenizer_path": "/path/to/dummy/tokenizer",
-        "is_generation": True,
-        "preferred_sampling_params": {"temperature": 0.7, "max_new_tokens": 128},
-    }
-    return ORJSONResponse(content=model_info)
+    global load_balancer
+
+    if not load_balancer or not load_balancer.prefill_servers:
+        raise HTTPException(
+            status_code=HTTPStatus.SERVICE_UNAVAILABLE,
+            detail="There is no server registered",
+        )
+
+    target_server_url = load_balancer.prefill_servers[0]
+    endpoint_url = f"{target_server_url}/get_model_info"
+
+    async with aiohttp.ClientSession() as session:
+        try:
+            async with session.get(endpoint_url) as response:
+                if response.status != 200:
+                    error_text = await response.text()
+                    raise HTTPException(
+                        status_code=HTTPStatus.BAD_GATEWAY,
+                        detail=(
+                            f"Failed to get model info from {target_server_url}"
+                            f"Status: {response.status}, Response: {error_text}"
+                        ),
+                    )
+
+                model_info_json = await response.json()
+                return ORJSONResponse(content=model_info_json)
+
+        except aiohttp.ClientError as e:
+            raise HTTPException(
+                status_code=HTTPStatus.SERVICE_UNAVAILABLE,
+                detail=f"Failed to get model info from backend",
+            )
 
 
 @app.post("/generate")