[diffusion] feat: gate /health and /health_generate on warmup completion and add liveness endpoint (#33787)

Co-authored-by: Mick <mickjagger19@icloud.com>

docs/docs/sglang-diffusion/api/cli.mdx

@@ -218,6 +218,24 @@ sglang serve \
   --port 30010
 ```
 
+### Health endpoints
+
+SGLang Diffusion separates process liveness from inference readiness:
+
+| Endpoint | Success condition | Recommended use |
+| --- | --- | --- |
+| `GET /liveness` | The HTTP server is accepting requests. It remains `200` during server warmup. | Kubernetes liveness probe |
+| `GET /health` | The server is ready for normal inference traffic. It returns `503` while server-based synthetic warmup is running and `200` after it completes. | Startup and readiness probes |
+| `GET /health_generate` | Compatibility alias for `/health`. It does not currently issue a generation request in SGLang Diffusion. | Existing integrations only |
+
+`/health` gates only server-based warmup. With `--warmup-mode off` or
+`--warmup-mode request`, it returns `200` once the HTTP server starts; those modes
+do not promise that compilation or other first-request work has completed. If
+server-based warmup fails, the server terminates instead of reporting ready.
+
+Do not use `/health` as a liveness probe: a long server warmup can legitimately
+keep it at `503` for several minutes.
+
 ### Cloud Storage
 
 SGLang Diffusion can upload generated images and videos to S3-compatible object storage after generation.

docs/docs/sglang-diffusion/deployment_cookbook.mdx

@@ -50,6 +50,33 @@ Base the decision on available memory on the selected GPU(s).
 - For multi-GPU deployment: the least-free selected GPU is the bottleneck. A busy 80GiB GPU can behave like a much smaller GPU.
 - For single-GPU deployment: FSDP shards DiT weights across multiple GPUs. It is not useful for keeping a single-GPU deployment on one GPU; for that case use CPU offload.
 
+## Health Probes
+
+Use `/liveness` to check that the HTTP process is alive and `/health` to check
+that the server is ready for inference. During server-based warmup, `/liveness`
+returns `200` while `/health` returns `503`. Configure the startup probe with a
+failure budget large enough for model loading and compilation:
+
+```yaml
+startupProbe:
+  httpGet:
+    path: /health
+    port: 30010
+  periodSeconds: 10
+  failureThreshold: 180
+readinessProbe:
+  httpGet:
+    path: /health
+    port: 30010
+livenessProbe:
+  httpGet:
+    path: /liveness
+    port: 30010
+```
+
+See [Health endpoints](/docs/sglang-diffusion/api/cli#health-endpoints) for the
+status-code contract and warmup-mode behavior.
+
 ## Performance Modes
 
 `--performance-mode` applies safe presets without overriding explicit offload, FSDP, or parallelism flags. `auto` is the default. Use `manual` when you need to keep performance-related server args under explicit user control. `--mode` is a short alias.

python/sglang/multimodal_gen/runtime/entrypoints/http_server.py

@@ -10,7 +10,7 @@ from typing import TYPE_CHECKING
 
 import httpx
 import torch
-from fastapi import APIRouter, FastAPI, Request
+from fastapi import APIRouter, FastAPI, Request, Response
 from fastapi.middleware.cors import CORSMiddleware
 
 from sglang.multimodal_gen.configs.sample.sampling_params import SamplingParams
@@ -52,6 +52,7 @@ logger = init_logger(__name__)
 
 VERTEX_ROUTE = os.environ.get("AIP_PREDICT_ROUTE", "/vertex_generate")
 SERVER_WARMUP_BYPASS_PATHS = (
+    "/liveness",
     "/health",
     "/health_generate",
     "/model_info",
@@ -59,26 +60,26 @@ SERVER_WARMUP_BYPASS_PATHS = (
 )
 
 
-async def _wait_until_http_ready(server_args: ServerArgs) -> None:
+async def _wait_until_http_live(server_args: ServerArgs) -> None:
     """for server warmup"""
-    health_url = f"{server_args.url()}/health"
-    # Probe the local server directly: a loopback readiness check must never be
+    liveness_url = f"{server_args.url()}/liveness"
+    # Probe the local server directly: a loopback liveness check must never be
     # routed through an HTTP proxy. trust_env=False also avoids crashing startup
     # on a malformed proxy env var, since httpx parses *_PROXY/NO_PROXY when the
     # client is constructed (raising httpx.InvalidURL before any request). See #28493.
     async with httpx.AsyncClient(trust_env=False) as client:
         for _ in range(120):
             try:
-                response = await client.get(health_url, timeout=5.0)
+                response = await client.get(liveness_url, timeout=5.0)
                 if response.status_code == 200:
                     return
             except httpx.HTTPError:
                 pass
             await asyncio.sleep(1.0)
-    raise RuntimeError(f"HTTP server did not become ready at {health_url}")
+    raise RuntimeError(f"HTTP server did not become live at {liveness_url}")
 
 
-async def _run_server_warmup_after_http_ready(
+async def _run_server_warmup_after_http_live(
     server_args: ServerArgs, warmup_done: asyncio.Event
 ) -> None:
     try:
@@ -86,7 +87,7 @@ async def _run_server_warmup_after_http_ready(
             warmup_done.set()
             return
 
-        await _wait_until_http_ready(server_args)
+        await _wait_until_http_live(server_args)
 
         await run_async_client_warmup(
             server_args,
@@ -120,7 +121,7 @@ async def lifespan(app: FastAPI):
     warmup_task = None
     if server_args.warmup_mode == "server":
         warmup_task = asyncio.create_task(
-            _run_server_warmup_after_http_ready(server_args, warmup_done)
+            _run_server_warmup_after_http_live(server_args, warmup_done)
         )
     else:
         warmup_done.set()
@@ -143,8 +144,17 @@ async def lifespan(app: FastAPI):
 health_router = APIRouter()
 
 
+@health_router.get("/liveness")
+async def liveness():
+    """Report that the HTTP server is accepting requests."""
+    return {"status": "ok"}
+
+
 @health_router.get("/health")
-async def health():
+async def health(request: Request):
+    """Report readiness for normal inference traffic."""
+    if not request.app.state.server_warmup_done.is_set():
+        return Response(status_code=503)
     return {"status": "ok"}
 
 
@@ -236,9 +246,9 @@ async def model_info_endpoint(request: Request):
 
 
 @health_router.get("/health_generate")
-async def health_generate():
-    # TODO : health generate endpoint
-    return {"status": "ok"}
+async def health_generate(request: Request):
+    """Compatibility readiness endpoint; no generation is issued."""
+    return await health(request)
 
 
 @health_router.get("/stats")

python/sglang/multimodal_gen/test/unit/test_health_warmup_gate.py

@@ -0,0 +1,94 @@
+"""Unit tests for diffusion server liveness and readiness endpoints.
+
+`/liveness` reports HTTP availability independently of model warmup.
+`/health` and `/health_generate` report readiness for inference traffic.
+"""
+
+import asyncio
+import unittest
+from types import SimpleNamespace
+from unittest import mock
+
+from sglang.multimodal_gen.runtime.entrypoints import http_server
+from sglang.multimodal_gen.runtime.entrypoints.http_server import (
+    health,
+    health_generate,
+    liveness,
+)
+
+
+def _make_request(warmup_done) -> SimpleNamespace:
+    state = SimpleNamespace(server_warmup_done=warmup_done)
+    return SimpleNamespace(app=SimpleNamespace(state=state))
+
+
+class TestHealthWarmupGate(unittest.IsolatedAsyncioTestCase):
+    async def test_liveness_returns_200_before_warmup(self):
+        self.assertEqual(await liveness(), {"status": "ok"})
+
+    async def test_health_returns_503_before_warmup(self):
+        warmup_done = asyncio.Event()
+        resp = await health(_make_request(warmup_done))
+        self.assertEqual(resp.status_code, 503)
+
+    async def test_health_returns_200_after_warmup(self):
+        warmup_done = asyncio.Event()
+        warmup_done.set()
+        resp = await health(_make_request(warmup_done))
+        self.assertEqual(resp, {"status": "ok"})
+
+    async def test_health_generate_returns_503_before_warmup(self):
+        warmup_done = asyncio.Event()
+        resp = await health_generate(_make_request(warmup_done))
+        self.assertEqual(resp.status_code, 503)
+
+    async def test_health_generate_returns_200_after_warmup(self):
+        warmup_done = asyncio.Event()
+        warmup_done.set()
+        resp = await health_generate(_make_request(warmup_done))
+        self.assertEqual(resp, {"status": "ok"})
+
+
+class _FakeResponse:
+    def __init__(self, status_code: int):
+        self.status_code = status_code
+
+
+class _FakeAsyncClient:
+    def __init__(self, status_codes: list[int]):
+        self._status_codes = iter(status_codes)
+        self.get_calls = 0
+        self.urls = []
+
+    def __call__(self, *args, **kwargs):
+        return self
+
+    async def __aenter__(self):
+        return self
+
+    async def __aexit__(self, *exc_info):
+        return False
+
+    async def get(self, url, timeout=None):
+        self.get_calls += 1
+        self.urls.append(url)
+        return _FakeResponse(next(self._status_codes))
+
+
+class TestWaitUntilHttpLive(unittest.IsolatedAsyncioTestCase):
+    async def test_waits_for_liveness_200(self):
+        fake_client = _FakeAsyncClient([503, 200])
+        server_args = SimpleNamespace(url=lambda: "http://127.0.0.1:11000")
+        with (
+            mock.patch.object(http_server.httpx, "AsyncClient", fake_client),
+            mock.patch.object(http_server.asyncio, "sleep", mock.AsyncMock()),
+        ):
+            await asyncio.wait_for(
+                http_server._wait_until_http_live(server_args), timeout=5.0
+            )
+        self.assertEqual(fake_client.get_calls, 2)
+        self.assertEqual(fake_client.urls, ["http://127.0.0.1:11000/liveness"] * 2)
+
+
+if __name__ == "__main__":
+    unittest.main()