[Bug]: vllm-openai nightly Docker image still fails due to missing pytest during EngineCore startup

[yasu-oh]

Your current environment

Docker image:
vllm/vllm-openai:nightly
https://hub.docker.com/layers/vllm/vllm-openai/nightly/images/sha256-2b5f940431016b25c461761cb813cebd1f02a9e4ba1069226a5c1c9ffb6834c6

vLLM version:
0.21.1rc1.dev262+g33d7cbe02

Model:
RedHatAI/gemma-4-31B-it-NVFP4

Related issue:
#43480

🐛 Describe the bug

I previously reported a similar startup failure in #43480, where the nightly Docker image failed because pytest was not installed and was imported indirectly via humming / cupy.testing.

After pulling a newer nightly image, the original failure path seems to have changed, but the server still fails to start because pytest is missing.

In this newer build, the model is loaded successfully, but EngineCore fails during startup while vLLM is initializing KV caches and running the profiling dummy run.

The failure path is now roughly:

EngineCore startup
  -> _initialize_kv_caches
  -> determine_available_memory
  -> gpu_worker.profile_run
  -> gpu_model_runner._dummy_run
  -> torch._dynamo AOT compile
  -> torch.distributed.tensor.experimental._context_parallel._cp_custom_ops
  -> torch.library.custom_op / _register_fake
  -> inspect.getframeinfo / inspect.getmodule
  -> cupy.testing
  -> import pytest
  -> ModuleNotFoundError: No module named 'pytest'

So this appears to be the same underlying runtime dependency / import side-effect issue as #43480, but it is now triggered from a different code path during EngineCore initialization rather than during the earlier quantization config verification path.

Since pytest is normally a test dependency, the official runtime Docker image should not require it for normal vLLM server startup.

Startup arguments

The server was started with the following non-default arguments shown in the log:

{
  'model_tag': 'RedHatAI/gemma-4-31B-it-NVFP4',
  'default_chat_template_kwargs': {'enable_thinking': True},
  'enable_auto_tool_choice': True,
  'tool_call_parser': 'gemma4',
  'host': '0.0.0.0',
  'model': 'RedHatAI/gemma-4-31B-it-NVFP4',
  'trust_remote_code': True,
  'max_model_len': 256000,
  'served_model_name': ['gemma4-31b'],
  'reasoning_parser': 'gemma4',
  'kv_cache_dtype': 'fp8',
  'mm_processor_kwargs': {'max_soft_tokens': 1120},
  'max_num_batched_tokens': 8192,
  'max_num_seqs': 32,
  'scheduler_reserve_full_isl': False,
  'async_scheduling': True,
  'optimization_level': '3'
}

Expected behavior

vllm/vllm-openai:nightly should start successfully without requiring the test dependency pytest.

If some runtime dependency indirectly imports cupy.testing, the Docker image should either include the required dependency or avoid importing test-only modules during normal server startup.

Actual behavior

The server fails during EngineCore initialization.

The important part of the traceback is:

File "/usr/local/lib/python3.12/dist-packages/vllm/v1/worker/gpu_worker.py", line 396, in determine_available_memory
    self.model_runner.profile_run()

File "/usr/local/lib/python3.12/dist-packages/vllm/v1/worker/gpu_model_runner.py", line 6164, in profile_run
    hidden_states, last_hidden_states = self._dummy_run(

File "/usr/local/lib/python3.12/dist-packages/vllm/v1/worker/gpu_model_runner.py", line 5824, in _dummy_run
    outputs = self.model(

File "/usr/local/lib/python3.12/dist-packages/vllm/model_executor/models/gemma4_mm.py", line 1487, in forward
    hidden_states = self.language_model.model(

File "/usr/local/lib/python3.12/dist-packages/vllm/compilation/decorators.py", line 663, in __call__
    self.aot_compiled_fn = self.aot_compile(*args, **kwargs)

File "/usr/local/lib/python3.12/dist-packages/torch/_dynamo/eval_frame.py", line 873, in aot_compile
    return aot_compile_fullgraph(

File "/usr/local/lib/python3.12/dist-packages/torch/distributed/tensor/experimental/_context_parallel/_cp_custom_ops.py", line 8, in <module>
    @torch.library.custom_op("cplib::flex_cp_allgather", mutates_args=())

File "/usr/local/lib/python3.12/dist-packages/torch/_library/utils.py", line 45, in get_source
    frame = inspect.getframeinfo(sys._getframe(stacklevel))

File "/usr/lib/python3.12/inspect.py", line 1007, in getmodule
    if ismodule(module) and hasattr(module, '__file__'):

File "/usr/local/lib/python3.12/dist-packages/cupy/testing/__init__.py", line 50, in <module>
    from cupy.testing._random import fix_random  # NOQA

File "/usr/local/lib/python3.12/dist-packages/cupy/testing/_random.py", line 11, in <module>
    import pytest

ModuleNotFoundError: No module named 'pytest'

Then the API server exits with:

RuntimeError: Engine core initialization failed. See root cause above. Failed core proc(s): {}

Notes

This does not look like a model download or Hugging Face authentication issue. The model checkpoint is loaded successfully before the failure.

This also does not look specific to the earlier humming import path reported in #43480. The new failure path goes through torch._dynamo / torch.distributed.tensor.experimental / cupy.testing, but it reaches the same root cause:

ModuleNotFoundError: No module named 'pytest'

Could you please check whether the nightly runtime image should include pytest, or whether cupy.testing should be avoided during normal vLLM server startup?

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[yasu-oh]

Additional workaround info:

I confirmed that the container starts successfully if I build a derived image with pytest installed manually:

FROM vllm/vllm-openai:nightly
RUN pip install pytest

So installing pytest works around this specific startup failure.

However, I still think this indicates that the runtime image is indirectly depending on a test-only dependency during normal server startup, probably through the cupy.testing import path shown in the traceback.

[khluu]

I also run into this

[ehfd]

I think reverting #42540 (#43492) didn't do anything, and humming was never the problem. The issue arose after 1fe3303 and before a5bbd81, and #43492 happened way before.

[scoobydont-666]

Still reproducing on cu129-nightly-aa2b56ffb0c1d8b29d6468282a49d9b4a9f0dd1c and cu129-nightly-6cbe448eed751824d608faf9078ef84724d621c1 (2026-05-26 + 2026-05-25 builds)

This issue was closed as completed on 2026-05-26 13:14 UTC, but the same bug reproduces on the cu129-nightly builds pushed both yesterday (2026-05-25) and today (2026-05-26):

• vllm/vllm-openai:cu129-nightly-aa2b56ffb0c1d8b29d6468282a49d9b4a9f0dd1c (2026-05-26)
• vllm/vllm-openai:cu129-nightly-6cbe448eed751824d608faf9078ef84724d621c1 (2026-05-25)

vLLM reports its version as 0.21.1rc1.dev270+g6cbe448ee for the older one.

Hardware + model

• GPU: NVIDIA RTX PRO 6000 Blackwell Workstation Edition (96GB, sm_120)
• Model: nvidia/Qwen3-14B-NVFP4
• Serve args: --quantization modelopt --max-model-len 32768 --kv-cache-dtype fp8 --gpu-memory-utilization 0.20 --enable-prefix-caching --tool-call-parser hermes

Identical failure path

EngineCore init
  -> gpu_worker.determine_available_memory
  -> gpu_model_runner.profile_run
  -> _dummy_run
  -> torch._dynamo aot_compile_fullgraph
  -> fullgraph_capture -> trace_frame
  -> VariableBuilder._wrap -> LocalMapWrappedHigherOrderVariable.should_wrap_in_hop
  -> torch.distributed.tensor.experimental._context_parallel._cp_custom_ops
  -> @torch.library.custom_op decorator
  -> CustomOpDef._register_to_dispatcher -> lib._register_fake
  -> torch._library.utils.get_source -> inspect.getframeinfo -> findsource -> getmodule
  -> walks loaded modules; hits cupy/testing/__init__.py:50
  -> `from cupy.testing._random import fix_random`
  -> cupy/testing/_random.py:11 `import pytest`
  -> ModuleNotFoundError: No module named 'pytest'
  -> EngineCore initialization failed

Workarounds for affected users — both verified working on our deploy:

Option A — --enforce-eager (perf cost ~10-15%, no infra change)

Avoids torch.compile + the dynamo trace path entirely. One-line vLLM arg addition.

Option B (recommended) — k8s initContainer + PYTHONPATH (no perf cost)

initContainers:
- name: install-pytest
  image: python:3.11-slim
  command: ["sh", "-c"]
  args:
    - |
      set -euo pipefail
      pip install --target=/extra-pkgs --no-cache-dir --quiet pytest
  volumeMounts:
  - name: extra-site-packages
    mountPath: /extra-pkgs
  securityContext:
    allowPrivilegeEscalation: false
    runAsNonRoot: true
    runAsUser: 1000
    capabilities: {drop: [ALL]}

containers:
- name: vllm
  image: vllm/vllm-openai:cu129-nightly-6cbe448e...
  env:
  - name: PYTHONPATH
    value: /opt/extra-site-packages
  volumeMounts:
  - name: extra-site-packages
    mountPath: /opt/extra-site-packages
    readOnly: true
  # ... rest of vllm container spec

volumes:
- name: extra-site-packages
  emptyDir: {sizeLimit: 256Mi}

Init container is ~6MB, ~5s install. Full torch.compile path is preserved.

Suggested upstream fixes (any one)

1. Make cupy.testing import lazy — cupy.testing.__init__ does an eager from cupy.testing._random import fix_random which transitively imports pytest. cupy upstream issue but cheap to file.
2. Add pytest to vllm-openai base image requirements — small image-size cost, surface-level fix.
3. Suppress the inspect.getframeinfo module walk in torch._library.utils.get_source — torch-side fix, narrower but cleanest.

Happy to file the cupy-side issue separately if useful. Requesting reopen since the recent close wasn't matched by the new nightlies.

[ehfd]

@scoobydont-666 #43530 was merged only 15 hours ago. The nightly will be out in a couple hours.

[ehfd]

Solved in nightly-1fc2cee50a09a094b9f2bbdfcb0ab0cadb536712.